[carveJwlIkooP6JGAAIwe30JlM.git] / player_skate.c

#ifndef PLAYER_SKATE_C
#define PLAYER_SKATE_C

#include "player.h"
#include "audio.h"

VG_STATIC void player__skate_bind( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   struct player_avatar *av = player->playeravatar;
   struct skeleton *sk = &av->sk;

   rb_update_transform( &player->rb );
   s->anim_stand           = skeleton_get_anim( sk, "pose_stand" );
   s->anim_highg           = skeleton_get_anim( sk, "pose_highg" );
   s->anim_air             = skeleton_get_anim( sk, "pose_air" );
   s->anim_slide           = skeleton_get_anim( sk, "pose_slide" );
   s->anim_push            = skeleton_get_anim( sk, "push" );
   s->anim_push_reverse    = skeleton_get_anim( sk, "push_reverse" );
   s->anim_ollie           = skeleton_get_anim( sk, "ollie" );
   s->anim_ollie_reverse   = skeleton_get_anim( sk, "ollie_reverse" );
   s->anim_grabs           = skeleton_get_anim( sk, "grabs" );
}

VG_STATIC void player__skate_kill_audio( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   audio_lock();
   if( s->aud_main )
      s->aud_main = audio_channel_fadeout( s->aud_main, 0.1f );
   if( s->aud_air )
      s->aud_air = audio_channel_fadeout( s->aud_air, 0.1f );
   if( s->aud_slide )
      s->aud_slide = audio_channel_fadeout( s->aud_slide, 0.1f );
   audio_unlock();
}

/* 
 * Collision detection routines
 *
 *
 */

/*
 * Does collision detection on a sphere vs world, and applies some smoothing
 * filters to the manifold afterwards
 */
VG_STATIC int skate_collide_smooth( player_instance *player,
                                    m4x3f mtx, rb_sphere *sphere,
                                    rb_ct *man )
{
   world_instance *world = get_active_world();

   int len = 0;
   len = rb_sphere__scene( mtx, sphere, NULL, &world->rb_geo.inf.scene, man );

   for( int i=0; i<len; i++ )
   {
      man[i].rba = &player->rb;
      man[i].rbb = NULL;
   }

   rb_manifold_filter_coplanar( man, len, 0.03f );

   if( len > 1 )
   {
      rb_manifold_filter_backface( man, len );
      rb_manifold_filter_joint_edges( man, len, 0.03f );
      rb_manifold_filter_pairs( man, len, 0.03f );
   }
   int new_len = rb_manifold_apply_filtered( man, len );
   if( len && !new_len )
      len = 1;
   else
      len = new_len;

   return len;
}

struct grind_info
{
   v3f co, dir, n;
};

VG_STATIC int skate_grind_scansq( player_instance *player,
                                  v3f pos, v3f dir, float r,
                                  struct grind_info *inf )
{
   world_instance *world = get_active_world();

   v4f plane;
   v3_copy( dir, plane );
   v3_normalize( plane );
   plane[3] = v3_dot( plane, pos );

   boxf box;
   v3_add( pos, (v3f){ r, r, r }, box[1] );
   v3_sub( pos, (v3f){ r, r, r }, box[0] );
   
   bh_iter it;
   bh_iter_init( 0, &it );
   int idx;

   struct grind_sample
   {
      v2f co;
      v2f normal;
      v3f normal3,
          centroid;
   }
   samples[48];
   int sample_count = 0;

   v2f support_min,
       support_max;

   v3f support_axis;
   v3_cross( plane, player->basis[1], support_axis );
   v3_normalize( support_axis );
   
   while( bh_next( world->geo_bh, &it, box, &idx ) ){
      u32 *ptri = &world->scene_geo->arrindices[ idx*3 ];
      v3f tri[3];

      struct world_surface *surf = world_tri_index_surface(world,ptri[0]);
      if( !(surf->info.flags & k_material_flag_skate_surface) )
         continue;

      for( int j=0; j<3; j++ )
         v3_copy( world->scene_geo->arrvertices[ptri[j]].co, tri[j] );

      for( int j=0; j<3; j++ ){
         int i0 = j,
             i1 = (j+1) % 3;
         
         struct grind_sample *sample = &samples[ sample_count ];
         v3f co;

         if( plane_segment( plane, tri[i0], tri[i1], co ) ){
            v3f d;
            v3_sub( co, pos, d );
            if( v3_length2( d ) > r*r )
               continue;

            v3f va, vb, normal;
            v3_sub( tri[1], tri[0], va );
            v3_sub( tri[2], tri[0], vb );
            v3_cross( va, vb, normal );

            sample->normal[0] = v3_dot( support_axis, normal );
            sample->normal[1] = v3_dot( player->basis[1], normal );
            sample->co[0]     = v3_dot( support_axis, d );
            sample->co[1]     = v3_dot( player->basis[1], d );

            v3_copy( normal, sample->normal3 ); /* normalize later
                                                   if we want to us it */

            v3_muls(                      tri[0], 1.0f/3.0f, sample->centroid );
            v3_muladds( sample->centroid, tri[1], 1.0f/3.0f, sample->centroid );
            v3_muladds( sample->centroid, tri[2], 1.0f/3.0f, sample->centroid );

            v2_normalize( sample->normal );
            sample_count ++;

            if( sample_count == vg_list_size( samples ) )
               goto too_many_samples;
         }
      }
   }

too_many_samples:

   if( sample_count < 2 )
      return 0;

   v3f 
       average_direction,
       average_normal;

   v2f min_co, max_co;
   v2_fill( min_co,  INFINITY );
   v2_fill( max_co, -INFINITY );

   v3_zero( average_direction );
   v3_zero( average_normal );

   int passed_samples = 0;
   
   for( int i=0; i<sample_count-1; i++ ){
      struct grind_sample *si, *sj;

      si = &samples[i];

      for( int j=i+1; j<sample_count; j++ ){
         if( i == j )
            continue;

         sj = &samples[j];

         /* non overlapping */
         if( v2_dist2( si->co, sj->co ) >= (0.01f*0.01f) )
            continue;

         /* not sharp angle */
         if( v2_dot( si->normal, sj->normal ) >= 0.7f )
            continue;

         /* not convex */
         v3f v0;
         v3_sub( sj->centroid, si->centroid, v0 );
         if( v3_dot( v0, si->normal3 ) >= 0.0f ||
             v3_dot( v0, sj->normal3 ) <= 0.0f )
            continue;

         v2_minv( sj->co, min_co, min_co );
         v2_maxv( sj->co, max_co, max_co );
         
         v3f n0, n1, dir;
         v3_copy( si->normal3, n0 );
         v3_copy( sj->normal3, n1 );
         v3_cross( n0, n1, dir );
         v3_normalize( dir );

         /* make sure the directions all face a common hemisphere */
         v3_muls( dir, vg_signf(v3_dot(dir,plane)), dir );
         v3_add( average_direction, dir, average_direction );

         float yi = v3_dot( player->basis[1], si->normal3 ),
               yj = v3_dot( player->basis[1], sj->normal3 );

         if( yi > yj )
            v3_add( si->normal3, average_normal, average_normal );
         else
            v3_add( sj->normal3, average_normal, average_normal );

         passed_samples ++;
      }
   }

   if( !passed_samples )
      return 0;

   if( (v3_length2( average_direction ) <= 0.001f) ||
       (v3_length2( average_normal ) <= 0.001f ) )
      return 0;

   float div = 1.0f/(float)passed_samples;
   v3_normalize( average_direction );
   v3_normalize( average_normal );

   v2f average_coord;
   v2_add( min_co, max_co, average_coord );
   v2_muls( average_coord, 0.5f, average_coord );

   v3_muls( support_axis, average_coord[0], inf->co );
   inf->co[1] += average_coord[1];
   v3_add( pos, inf->co, inf->co );
   v3_copy( average_normal, inf->n );
   v3_copy( average_direction, inf->dir );

   vg_line_pt3( inf->co, 0.02f, VG__GREEN );
   vg_line_arrow( inf->co, average_direction, 0.3f, VG__GREEN );
   vg_line_arrow( inf->co, inf->n, 0.2f, VG__CYAN );

   return passed_samples;
}

VG_STATIC int solve_prediction_for_target( player_instance *player,
                                           v3f target, float max_angle,
                                           struct land_prediction *p )
{
   /* calculate the exact solution(s) to jump onto that grind spot */

   v3f v0;
   v3_sub( target, player->rb.co, v0 );
   m3x3_mulv( player->invbasis, v0, v0 );

   v3f ax;
   v3_copy( v0, ax );
   ax[1] = 0.0f;
   v3_normalize( ax );

   v3f v_local;
   m3x3_mulv( player->invbasis, player->rb.v, v_local );

   v2f d = { v3_dot( ax, v0 ),           v0[1] },
       v = { v3_dot( ax, player->rb.v ), v_local[1] };

   float a = atan2f( v[1], v[0] ),
         m = v2_length( v ),
         root = m*m*m*m - p->gravity*(p->gravity*d[0]*d[0] + 2.0f*d[1]*m*m);

   if( root > 0.0f )
   {
      root = sqrtf( root );
      float a0 = atanf( (m*m + root) / (p->gravity * d[0]) ),
            a1 = atanf( (m*m - root) / (p->gravity * d[0]) );

      if( fabsf(a0-a) > fabsf(a1-a) )
         a0 = a1;

      if( fabsf(a0-a) > max_angle )
         return 0;

      /* TODO: sweep the path before chosing the smallest dist */

      p->log_length = 0;
      p->land_dist = 0.0f;
      v3_zero( p->apex );
      p->type = k_prediction_grind;

      v3_muls( ax, cosf( a0 ) * m, p->v );
      p->v[1] += sinf( a0 ) * m;
      m3x3_mulv( player->basis, p->v, p->v );

      p->land_dist = d[0] / (cosf(a0)*m);

      /* add a trace */
      for( int i=0; i<=20; i++ )
      {
         float t = (float)i * (1.0f/20.0f) * p->land_dist;

         v3f p0;
         v3_muls( p->v, t, p0 );
         v3_muladds( p0, player->basis[1], -0.5f * p->gravity * t*t, p0 );

         v3_add( player->rb.co, p0, p->log[ p->log_length ++ ] );
      }

      return 1;
   }
   else
      return 0;
}

VG_STATIC 
void player__approximate_best_trajectory( player_instance *player )
{
   world_instance *world = get_active_world();

   struct player_skate *s = &player->_skate;
   float k_trace_delta = k_rb_delta * 10.0f;

   s->state.air_start = vg.time;
   v3_copy( player->rb.v, s->state.air_init_v );
   v3_copy( player->rb.co, s->state.air_init_co );

   s->prediction_count = 0;

   v3f axis;
   v3_cross( player->rb.v, player->rb.to_world[1], axis );
   v3_normalize( axis );

   /* at high slopes, Y component is low */
   float upness      = v3_dot( player->rb.to_world[1], player->basis[1] ),
         angle_begin = -(1.0f-fabsf( upness )),
         angle_end   =   1.0f;

   struct grind_info grind;
   int grind_located = 0;

   for( int m=0;m<=30; m++ )
   {
      struct land_prediction *p = &s->predictions[ s->prediction_count ++ ];

      p->log_length = 0;
      p->land_dist = 0.0f;
      v3_zero( p->apex );
      p->type = k_prediction_none;

      v3f launch_co, launch_v, co0, co1;
      v3_copy( player->rb.co, launch_co );
      v3_copy( player->rb.v,  launch_v );
      v3_copy( launch_co, co0 );

      float vt  = (float)m * (1.0f/30.0f),
            ang = vg_lerpf( angle_begin, angle_end, vt ) * 0.15f;

      v4f qbias;
      q_axis_angle( qbias, axis, ang );
      q_mulv( qbias, launch_v, launch_v );

      float yaw_sketch = 1.0f-fabsf(upness);

      float yaw_bias = ((float)(m%3) - 1.0f) * 0.08f * yaw_sketch;
      q_axis_angle( qbias, player->rb.to_world[1], yaw_bias );
      q_mulv( qbias, launch_v, launch_v );


      float gravity_bias = vg_lerpf( 0.85f, 1.4f, vt ),
            gravity      = k_gravity * gravity_bias;
      p->gravity = gravity;

      v3_copy( launch_v, p->v );

      m3x3f basis;
      m3x3_copy( player->basis, basis );

      for( int i=1; i<=50; i++ )
      {
         float t = (float)i * k_trace_delta;

         v3_muls( launch_v, t, co1 );
         v3_muladds( co1, basis[1], -0.5f * gravity * t*t, co1 );
         v3_add( launch_co, co1, co1 );

         float launch_vy = v3_dot( launch_v,basis[1] );
         if( !grind_located && (launch_vy - gravity*t < 0.0f) )
         {
            v3f closest;
            if( bh_closest_point( world->geo_bh, co1, closest, 1.0f ) != -1 )
            {
               v3f ve;
               v3_copy( launch_v, ve );
               v3_muladds( ve, basis[1], -gravity * t, ve );

               if( skate_grind_scansq( player, closest, ve, 0.5f, &grind ) )
               {
                  /* check alignment */
                  v2f v0 = { v3_dot( ve, basis[0] ), 
                             v3_dot( ve, basis[2] ) },
                      v1 = { v3_dot( grind.dir, basis[0] ), 
                             v3_dot( grind.dir, basis[2] ) };

                  v2_normalize( v0 );
                  v2_normalize( v1 );

                  float a = v2_dot( v0, v1 );

                  if( a >= cosf( VG_PIf * 0.185f ) )
                  {
                     grind_located = 1;
                  }
               }
            }
         }

         if( world->rendering_gate ){
            ent_gate *gate = world->rendering_gate;
            if( gate_intersect( gate, co1, co0 ) ){
               m4x3_mulv( gate->transport, co0, co0 );
               m4x3_mulv( gate->transport, co1, co1 );
               m3x3_mulv( gate->transport, launch_v, launch_v);
               m4x3_mulv( gate->transport, launch_co, launch_co );
               m3x3_mul( gate->transport, basis, basis );
            }
         }

         float t1;
         v3f n;

         int idx = spherecast_world( world, co0, co1, k_board_radius, &t1, n );
         if( idx != -1 )
         {
            v3f co;
            v3_lerp( co0, co1, t1, co );
            v3_copy( co, p->log[ p->log_length ++ ] ); 

            v3_copy( n, p->n );
            p->type = k_prediction_land;

            v3f ve;
            v3_copy( launch_v, ve );
            v3_muladds( ve, player->basis[1], -gravity * t, ve );

            struct grind_info replace_grind;
            if( skate_grind_scansq( player, co, ve, 0.3f, &replace_grind ) )
            {
               v3_copy( replace_grind.n, p->n );
               p->type = k_prediction_grind;
            }

            p->score = -v3_dot( ve, p->n );
            p->land_dist = t + k_trace_delta * t1;

            u32 vert_index = world->scene_geo->arrindices[ idx*3 ];
            struct world_surface *surf = 
               world_tri_index_surface( world, vert_index );
            
            /* Bias prediction towords ramps */
            if( !(surf->info.flags & k_material_flag_skate_surface) )
               p->score *= 10.0f;

            break;
         }
         
         if( i % 3 == 0 )
            v3_copy( co1, p->log[ p->log_length ++ ] ); 

         v3_copy( co1, co0 );
      }

      if( p->type == k_prediction_none )
         s->prediction_count --;
   }

   if( grind_located ){
      /* calculate the exact solution(s) to jump onto that grind spot */
      struct land_prediction *p = &s->predictions[ s->prediction_count ];
      p->gravity = k_gravity;

      if( solve_prediction_for_target( player, grind.co, 0.125f*VG_PIf, p ) ){
         v3_copy( grind.n, p->n );

         /* determine score */
         v3f ve;
         v3_copy( p->v, ve );
         v3_muladds( ve, player->basis[1], -p->gravity * p->land_dist, ve );
         p->score = -v3_dot( ve, grind.n ) * 0.85f;

         s->prediction_count ++;
      }
   }


   float score_min =  INFINITY,
         score_max = -INFINITY;

   struct land_prediction *best = NULL;

   for( int i=0; i<s->prediction_count; i ++ ){
      struct land_prediction *p = &s->predictions[i];

      if( p->score < score_min )
         best = p;

      score_min = vg_minf( score_min, p->score );
      score_max = vg_maxf( score_max, p->score );
   }

   for( int i=0; i<s->prediction_count; i ++ ){
      struct land_prediction *p = &s->predictions[i];
      float s = p->score;

      s -= score_min;
      s /= (score_max-score_min);
      s  = 1.0f - s;

      p->score = s;
      p->colour = s * 255.0f;

      if( p == best )
         p->colour <<= 16;
      else if( p->type == k_prediction_land )
         p->colour <<= 8;
      
      p->colour |= 0xff000000;
   }

   if( best ){
      v3_copy( best->n, s->land_normal );
      v3_copy( best->v, player->rb.v );
      s->land_dist = best->land_dist;

      v2f steer = { player->input_js1h->axis.value,
                    player->input_js1v->axis.value };
      v2_normalize_clamp( steer );
      s->state.gravity_bias = best->gravity;

      if( (fabsf(steer[1]) > 0.5f) && (s->land_dist >= 1.5f) ){
         s->state.flip_rate = (1.0f/s->land_dist) * vg_signf(steer[1]) *
                                 s->state.reverse ;
         s->state.flip_time = 0.0f;
         v3_copy( player->rb.to_world[0], s->state.flip_axis );
      }
      else{
         s->state.flip_rate = 0.0f;
         v3_zero( s->state.flip_axis );
      }
   }
   else{
      v3_copy( player->basis[1], s->land_normal );
   }
}

/*
 *
 * Varius physics models
 * ------------------------------------------------
 */

/*
 * Air control, no real physics
 */
VG_STATIC void skate_apply_air_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   if( s->state.activity_prev != k_skate_activity_air )
      player__approximate_best_trajectory( player );

   float angle = v3_dot( player->rb.to_world[1], s->land_normal );
   angle = vg_clampf( angle, -1.0f, 1.0f );
   v3f axis; 
   v3_cross( player->rb.to_world[1], s->land_normal, axis );

   v4f correction;
   q_axis_angle( correction, axis, 
                  acosf(angle)*2.0f*VG_TIMESTEP_FIXED );
   q_mul( correction, player->rb.q, player->rb.q );

   v2f steer = { player->input_js1h->axis.value,
                 player->input_js1v->axis.value };
   v2_normalize_clamp( steer );
}

VG_STATIC int player_skate_trick_input( player_instance *player );
VG_STATIC void skate_apply_trick_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   v3f Fd, Fs, F;
   v3f strength = { 3.7f, 3.6f, 8.0f };

   v3_muls( s->board_trick_residualv, -4.0f , Fd );
   v3_muls( s->board_trick_residuald, -10.0f, Fs );
   v3_add( Fd, Fs, F );
   v3_mul( strength, F, F );

   v3_muladds( s->board_trick_residualv, F, k_rb_delta, 
               s->board_trick_residualv );
   v3_muladds( s->board_trick_residuald, s->board_trick_residualv,
               k_rb_delta, s->board_trick_residuald );

   if( s->state.activity == k_skate_activity_air ){
      if( v3_length2( s->state.trick_vel ) < 0.0001f )
         return;

      int carry_on = player_skate_trick_input( player );

      /* we assume velocities share a common divisor, in which case the 
       * interval is the minimum value (if not zero) */

      float min_rate = 99999.0f;

      for( int i=0; i<3; i++ ){
         float v = s->state.trick_vel[i];
         if( (v > 0.0f) && (v < min_rate) )
            min_rate = v;
      }

      float interval = 1.0f / min_rate,
            current  = floorf( s->state.trick_time / interval ),
            next_end = (current+1.0f) * interval;


      /* integrate trick velocities */
      v3_muladds( s->state.trick_euler, s->state.trick_vel, k_rb_delta,
                  s->state.trick_euler );

      if( !carry_on && (s->state.trick_time + k_rb_delta >= next_end) ){
         s->state.trick_time = 0.0f;
         s->state.trick_euler[0] = roundf( s->state.trick_euler[0] );
         s->state.trick_euler[1] = roundf( s->state.trick_euler[1] );
         s->state.trick_euler[2] = roundf( s->state.trick_euler[2] );
         v3_copy( s->state.trick_vel, s->board_trick_residualv );
         v3_zero( s->state.trick_vel );
      }

      s->state.trick_time += k_rb_delta;
   }
   else{
      if( (v3_length2(s->state.trick_vel) >= 0.0001f ) &&
          s->state.trick_time > 0.2f)
      {
         player__skate_kill_audio( player );
         player__dead_transition( player );
      }

      s->state.trick_euler[0] = roundf( s->state.trick_euler[0] );
      s->state.trick_euler[1] = roundf( s->state.trick_euler[1] );
      s->state.trick_euler[2] = roundf( s->state.trick_euler[2] );
      s->state.trick_time = 0.0f;
      v3_zero( s->state.trick_vel );
   }
}

VG_STATIC void skate_apply_grab_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   float grabt = player->input_grab->axis.value;

   if( grabt > 0.5f ){
      v2_muladds( s->state.grab_mouse_delta, vg.mouse_delta, 0.02f, 
                  s->state.grab_mouse_delta );

      v2_normalize_clamp( s->state.grab_mouse_delta );
   }
   else
      v2_zero( s->state.grab_mouse_delta );

   s->state.grabbing = vg_lerpf( s->state.grabbing, grabt, 8.4f*k_rb_delta );
}

VG_STATIC void skate_apply_steering_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   /* Steering */
   float steer = player->input_js1h->axis.value,
         grab  = player->input_grab->axis.value;

   steer = vg_signf( steer ) * steer*steer * k_steer_ground;

   v3f steer_axis;
   v3_muls( player->rb.to_world[1], -vg_signf( steer ), steer_axis );

   float rate = 26.0f,
         top  = 1.0f;

   if( s->state.activity == k_skate_activity_air ){
      rate = 6.0f * fabsf(steer);
      top  = 1.5f;
   }
   else{
      /* rotate slower when grabbing on ground */
      steer *= (1.0f-(s->state.jump_charge+grab)*0.4f);

      if( s->state.activity == k_skate_activity_grind_5050 ){
         rate = 0.0f;
         top  = 0.0f;
      }

      else if( s->state.activity >= k_skate_activity_grind_any ){
         rate *= fabsf(steer);

         float a = 0.8f * -steer * k_rb_delta;

         v4f q;
         q_axis_angle( q, player->rb.to_world[1], a );
         q_mulv( q, s->grind_vec, s->grind_vec );

         v3_normalize( s->grind_vec );
      }

      else if( s->state.manual_direction ){
         rate = 35.0f;
         top  = 1.5f;
      }
   }

   float current  = v3_dot( player->rb.to_world[1], player->rb.w ),
         addspeed = (steer * -top) - current,
         maxaccel = rate * k_rb_delta,
         accel    = vg_clampf( addspeed, -maxaccel, maxaccel );

   v3_muladds( player->rb.w, player->rb.to_world[1], accel, player->rb.w );
}

/*
 * Computes friction and surface interface model
 */
VG_STATIC void skate_apply_friction_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   /*
    * Computing localized friction forces for controlling the character
    * Friction across X is significantly more than Z
    */

   v3f vel;
   m3x3_mulv( player->rb.to_local, player->rb.v, vel );
   float slip = 0.0f;
   
   if( fabsf(vel[2]) > 0.01f )
      slip = fabsf(-vel[0] / vel[2]) * vg_signf(vel[0]);

   if( fabsf( slip ) > 1.2f )
      slip = vg_signf( slip ) * 1.2f;

   s->state.slip = slip;
   s->state.reverse = -vg_signf(vel[2]);

   vel[0] += vg_cfrictf( vel[0], k_friction_lat * k_rb_delta );
   vel[2] += vg_cfrictf( vel[2], k_friction_resistance * k_rb_delta );

   /* Pushing additive force */

   if( !player->input_jump->button.value ){
      if( player->input_push->button.value || 
          (vg.time-s->state.start_push<0.75) )
      {
         if( (vg.time - s->state.cur_push) > 0.25 )
            s->state.start_push = vg.time;

         s->state.cur_push = vg.time;

         double push_time = vg.time - s->state.start_push;

         float cycle_time = push_time*k_push_cycle_rate,
               accel      = k_push_accel * (sinf(cycle_time)*0.5f+0.5f),
               amt        = accel * VG_TIMESTEP_FIXED,
               current    = v3_length( vel ),
               new_vel    = vg_minf( current + amt, k_max_push_speed ),
               delta      = new_vel - vg_minf( current, k_max_push_speed );

         vel[2] += delta * -s->state.reverse;
      }
   }

   /* Send back to velocity */
   m3x3_mulv( player->rb.to_world, vel, player->rb.v );
}

VG_STATIC void skate_apply_jump_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   int charging_jump_prev = s->state.charging_jump;
   s->state.charging_jump = player->input_jump->button.value;

   /* Cannot charge this in air */
   if( s->state.activity == k_skate_activity_air ){
      s->state.charging_jump = 0;
      return;
   }

   if( s->state.charging_jump ){
      s->state.jump_charge += k_rb_delta * k_jump_charge_speed;

      if( !charging_jump_prev )
         s->state.jump_dir = s->state.reverse>0.0f? 1: 0;
   }
   else{
      s->state.jump_charge -= k_jump_charge_speed * k_rb_delta;
   }

   s->state.jump_charge = vg_clampf( s->state.jump_charge, 0.0f, 1.0f );

   /* player let go after charging past 0.2: trigger jump */
   if( (!s->state.charging_jump) && (s->state.jump_charge > 0.2f) ){
      v3f jumpdir;
      
      /* Launch more up if alignment is up else improve velocity */
      float aup = v3_dot( player->basis[1], player->rb.to_world[1] ),
            mod = 0.5f,
            dir = mod + fabsf(aup)*(1.0f-mod);

      v3_copy( player->rb.v, jumpdir );
      v3_normalize( jumpdir );
      v3_muls( jumpdir, 1.0f-dir, jumpdir );
      v3_muladds( jumpdir, player->rb.to_world[1], dir, jumpdir );
      v3_normalize( jumpdir );
      
      float force = k_jump_force*s->state.jump_charge;
      v3_muladds( player->rb.v, jumpdir, force, player->rb.v );
      s->state.jump_charge = 0.0f;
      s->state.jump_time = vg.time;
      s->state.activity = k_skate_activity_air;

      v2f steer = { player->input_js1h->axis.value,
                    player->input_js1v->axis.value };
      v2_normalize_clamp( steer );
      skate_apply_air_model( player );

#if 0
      float maxspin = k_steer_air * k_rb_delta * k_spin_boost;
      s->state.steery_s = -steer[0] * maxspin;
      s->state.steerx = s->state.steerx_s;
      s->state.lift_frames ++;
#endif

      audio_lock();
      audio_oneshot_3d( &audio_jumps[rand()%2], player->rb.co, 40.0f, 1.0f );
      audio_unlock();
   }
}

VG_STATIC void skate_apply_pump_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   if( s->state.activity != k_skate_activity_ground ){
      v3_zero( s->state.throw_v );
      return;
   }

   /* Throw / collect routine 
    *
    * TODO: Max speed boost
    */
   if( player->input_grab->axis.value > 0.5f ){
      if( s->state.activity == k_skate_activity_ground ){
         /* Throw */
         v3_muls( player->rb.to_world[1], k_mmthrow_scale, s->state.throw_v );
      }
   }
   else{
      /* Collect */
      float doty = v3_dot( player->rb.to_world[1], s->state.throw_v );
      
      v3f Fl, Fv;
      v3_muladds( s->state.throw_v, player->rb.to_world[1], -doty, Fl);

      if( s->state.activity == k_skate_activity_ground ){
         v3_muladds( player->rb.v,     Fl,  k_mmcollect_lat, player->rb.v );
         v3_muladds( s->state.throw_v, Fl, -k_mmcollect_lat, s->state.throw_v );
      }

      v3_muls( player->rb.to_world[1], -doty, Fv );
      v3_muladds( player->rb.v,     Fv, k_mmcollect_vert, player->rb.v );
      v3_muladds( s->state.throw_v, Fv, k_mmcollect_vert, s->state.throw_v );
   }

   /* Decay */
   if( v3_length2( s->state.throw_v ) > 0.0001f ){
      v3f dir;
      v3_copy( s->state.throw_v, dir );
      v3_normalize( dir );

      float max = v3_dot( dir, s->state.throw_v ),
            amt = vg_minf( k_mmdecay * k_rb_delta, max );
      v3_muladds( s->state.throw_v, dir, -amt, s->state.throw_v );
   }
}

VG_STATIC void skate_apply_cog_model( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   v3f ideal_cog, ideal_diff, ideal_dir;
   v3_copy( s->state.up_dir, ideal_dir );
   v3_normalize( ideal_dir );

   v3_muladds( player->rb.co, ideal_dir,
               1.0f-player->input_grab->axis.value, ideal_cog );
   v3_sub( ideal_cog, s->state.cog, ideal_diff );

   /* Apply velocities */
   v3f rv;
   v3_sub( player->rb.v, s->state.cog_v, rv );

   v3f F;
   v3_muls( ideal_diff, -k_cog_spring * k_rb_rate, F );
   v3_muladds( F, rv,   -k_cog_damp * k_rb_rate, F );

   float ra = k_cog_mass_ratio,
         rb = 1.0f-k_cog_mass_ratio;

   /* Apply forces & intergrate */
   v3_muladds( s->state.cog_v, F, -rb, s->state.cog_v );
   v3_muladds( s->state.cog_v, player->basis[1], -9.8f * k_rb_delta,
               s->state.cog_v );

   v3_muladds( s->state.cog, s->state.cog_v, k_rb_delta, s->state.cog );
}


VG_STATIC void skate_integrate( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   float decay_rate = 1.0f - (k_rb_delta * 3.0f),
         decay_rate_y = 1.0f;

   if( s->state.activity >= k_skate_activity_grind_any ){
      decay_rate = 1.0f-vg_lerpf( 3.0f, 20.0f, s->grind_strength ) * k_rb_delta;
      decay_rate_y = decay_rate;
   }

   float wx = v3_dot( player->rb.w, player->rb.to_world[0] ) * decay_rate,
         wy = v3_dot( player->rb.w, player->rb.to_world[1] ) * decay_rate_y,
         wz = v3_dot( player->rb.w, player->rb.to_world[2] ) * decay_rate;

   v3_muls(                  player->rb.to_world[0], wx, player->rb.w );
   v3_muladds( player->rb.w, player->rb.to_world[1], wy, player->rb.w );
   v3_muladds( player->rb.w, player->rb.to_world[2], wz, player->rb.w );

   s->state.flip_time += s->state.flip_rate * k_rb_delta;
   rb_update_transform( &player->rb );
}

/*
 * 1 2 or 3
 */

VG_STATIC int player_skate_trick_input( player_instance *player )
{
   return (player->input_trick0->button.value) |
          (player->input_trick1->button.value << 1) |
          (player->input_trick2->button.value << 1) |
          (player->input_trick2->button.value);
}

VG_STATIC void player__skate_pre_update( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   if( vg_input_button_down( player->input_use ) ){
      player->subsystem = k_player_subsystem_walk;

      v3f angles;
      v3_copy( player->cam.angles, angles );
      angles[2] = 0.0f;

      player->holdout_time = 0.25f;
      player__skate_kill_audio( player );
      player__walk_transition( player, angles );
      return;
   }

   if( vg_input_button_down( player->input_reset ) ){
      player->rb.co[1] += 2.0f;
      s->state.cog[1] += 2.0f;
      q_axis_angle( player->rb.q, (v3f){1.0f,0.0f,0.0f}, VG_PIf * 0.25f );
      v3_zero( player->rb.w );
      v3_zero( player->rb.v );

      rb_update_transform( &player->rb );
   }

   int trick_id; 
   if( (s->state.activity == k_skate_activity_air) && 
       (trick_id = player_skate_trick_input( player )) )
   {
      if( (vg.time - s->state.jump_time) < 0.1f ){
         v3_zero( s->state.trick_vel );
         s->state.trick_time = 0.0f;

         if( trick_id == 1 ){
            s->state.trick_vel[0] = 3.0f;
         }
         else if( trick_id == 2 ){
            s->state.trick_vel[2] = 3.0f;
         }
         else if( trick_id == 3 ){
            s->state.trick_vel[0] = 2.0f;
            s->state.trick_vel[2] = 2.0f;
         }
      }
   }
}

VG_STATIC void player__skate_post_update( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   for( int i=0; i<s->prediction_count; i++ )
   {
      struct land_prediction *p = &s->predictions[i];
      
      for( int j=0; j<p->log_length - 1; j ++ )
      {
         float brightness = p->score*p->score*p->score;
         v3f p1;
         v3_lerp( p->log[j], p->log[j+1], brightness, p1 );
         vg_line( p->log[j], p1, p->colour );
      }

      vg_line_cross( p->log[p->log_length-1], p->colour, 0.25f );

      v3f p1;
      v3_add( p->log[p->log_length-1], p->n, p1 );
      vg_line( p->log[p->log_length-1], p1, 0xffffffff );

      vg_line_pt3( p->apex, 0.02f, 0xffffffff );
   }

#if 0
   vg_line_pt3( s->state.apex, 0.030f, 0xff0000ff );
#endif

   audio_lock();

   float air   = s->state.activity == k_skate_activity_air? 1.0f: 0.0f,
         speed = v3_length( player->rb.v ),
         attn  = vg_minf( 1.0f, speed*0.1f ),
         slide = vg_clampf( fabsf(s->state.slip), 0.0f, 1.0f ),

         vol_main    = sqrtf( (1.0f-air)*attn*(1.0f-slide) * 0.4f ),
         vol_air     = sqrtf(       air *attn * 0.5f ),
         vol_slide   = sqrtf( (1.0f-air)*attn*slide * 0.25f );

   const u32 flags = AUDIO_FLAG_SPACIAL_3D|AUDIO_FLAG_LOOP;
   if( !s->aud_main )
      s->aud_main = audio_request_channel( &audio_board[0], flags );

   if( !s->aud_air )
      s->aud_air = audio_request_channel( &audio_board[1], flags );

   if( !s->aud_slide )
      s->aud_slide = audio_request_channel( &audio_board[2], flags );


   /* brrrrrrrrrrrt sound for tiles and stuff 
    * --------------------------------------------------------*/
   float sidechain_amt = 0.0f,
         hz            = speed * 2.0f;

   if( s->surface == k_surface_prop_tiles )
      sidechain_amt = 1.0f;
   else
      sidechain_amt = 0.0f;

   audio_set_lfo_frequency( 0, hz );
   audio_set_lfo_wave( 0, k_lfo_polynomial_bipolar, 
                        vg_lerpf( 250.0f, 80.0f, attn ) );

   if( s->aud_main ){
      s->aud_main->colour = 0x00103efe;
      audio_channel_set_spacial( s->aud_main, player->rb.co, 40.0f );
      audio_channel_slope_volume( s->aud_main, 0.05f, vol_main );
      audio_channel_sidechain_lfo( s->aud_main, 0, sidechain_amt );

      float rate = 1.0f + (attn-0.5f)*0.2f;
      audio_channel_set_sampling_rate( s->aud_main, rate );
   }

   if( s->aud_slide ){
      s->aud_slide->colour = 0x00103efe;
      audio_channel_set_spacial( s->aud_slide, player->rb.co, 40.0f );
      audio_channel_slope_volume( s->aud_slide, 0.05f, vol_slide );
      audio_channel_sidechain_lfo( s->aud_slide, 0, sidechain_amt );
   }

   if( s->aud_air ){
      s->aud_air->colour = 0x00103efe;
      audio_channel_set_spacial( s->aud_air, player->rb.co, 40.0f );
      audio_channel_slope_volume( s->aud_air, 0.05f, vol_air );
   }

   audio_unlock();
}

/*
 * truck alignment model at ra(local)
 * returns 1 if valid surface:
 *             surface_normal will be filled out with an averaged normal vector
 *             axel_dir will be the direction from left to right wheels
 *
 * returns 0 if no good surface found
 */
VG_STATIC 
int skate_compute_surface_alignment( player_instance *player,
                                     v3f ra, u32 colour,
                                     v3f surface_normal, v3f axel_dir )
{
   struct player_skate *s = &player->_skate;
   world_instance *world = get_active_world();

   v3f truck, left, right;
   m4x3_mulv( player->rb.to_world, ra, truck );

   v3_muladds( truck, player->rb.to_world[0], -k_board_width, left  );
   v3_muladds( truck, player->rb.to_world[0],  k_board_width, right );
   vg_line( left, right, colour );

   float k_max_truck_flex = VG_PIf * 0.25f;
   
   ray_hit ray_l, ray_r;

   v3f dir;
   v3_muls( player->rb.to_world[1], -1.0f, dir );

   int res_l = 0, res_r = 0;

   for( int i=0; i<8; i++ )
   {
      float t = 1.0f - (float)i * (1.0f/8.0f);
      v3_muladds( truck, player->rb.to_world[0], -k_board_radius*t, left );
      v3_muladds( left,  player->rb.to_world[1],  k_board_radius,   left );
      ray_l.dist = 2.1f * k_board_radius;

      res_l = ray_world( world, left, dir, &ray_l );

      if( res_l )
         break;
   }

   for( int i=0; i<8; i++ )
   {
      float t = 1.0f - (float)i * (1.0f/8.0f);
      v3_muladds( truck, player->rb.to_world[0],  k_board_radius*t, right );
      v3_muladds( right, player->rb.to_world[1],  k_board_radius,   right );
      ray_r.dist = 2.1f * k_board_radius;

      res_r = ray_world( world, right, dir, &ray_r );

      if( res_r )
         break;
   }

   v3f v0;
   v3f midpoint;
   v3f tangent_average;
   v3_muladds( truck, player->rb.to_world[1], -k_board_radius, midpoint );
   v3_zero( tangent_average );

   if( res_l || res_r )
   {
      v3f p0, p1, t;
      v3_copy( midpoint, p0 );
      v3_copy( midpoint, p1 );

      if( res_l ) 
      {
         v3_copy( ray_l.pos, p0 );
         v3_cross( ray_l.normal, player->rb.to_world[0], t );
         v3_add( t, tangent_average, tangent_average );
      }
      if( res_r )
      {
         v3_copy( ray_r.pos, p1 );
         v3_cross( ray_r.normal, player->rb.to_world[0], t );
         v3_add( t, tangent_average, tangent_average );
      }

      v3_sub( p1, p0, v0 );
      v3_normalize( v0 );
   }
   else
   {
      /* fallback: use the closes point to the trucks */
      v3f closest;
      int idx = bh_closest_point( world->geo_bh, midpoint, closest, 0.1f );

      if( idx != -1 )
      {
         u32 *tri = &world->scene_geo->arrindices[ idx * 3 ];
         v3f verts[3];

         for( int j=0; j<3; j++ )
            v3_copy( world->scene_geo->arrvertices[ tri[j] ].co, verts[j] );

         v3f vert0, vert1, n;
         v3_sub( verts[1], verts[0], vert0 );
         v3_sub( verts[2], verts[0], vert1 );
         v3_cross( vert0, vert1, n );
         v3_normalize( n );

         if( v3_dot( n, player->rb.to_world[1] ) < 0.3f )
            return 0;

         v3_cross( n, player->rb.to_world[2], v0 );
         v3_muladds( v0, player->rb.to_world[2],
                     -v3_dot( player->rb.to_world[2], v0 ), v0 );
         v3_normalize( v0 );

         v3f t;
         v3_cross( n, player->rb.to_world[0], t );
         v3_add( t, tangent_average, tangent_average );
      }
      else
         return 0;
   }

   v3_muladds( truck, v0,  k_board_width, right );
   v3_muladds( truck, v0, -k_board_width, left );

   vg_line( left, right, VG__WHITE );

   v3_normalize( tangent_average );
   v3_cross( v0, tangent_average, surface_normal );
   v3_copy( v0, axel_dir );

   return 1;
}

VG_STATIC void skate_weight_distribute( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   v3_zero( s->weight_distribution );

   int reverse_dir = v3_dot( player->rb.to_world[2], player->rb.v ) < 0.0f?1:-1;

   if( s->state.manual_direction == 0 )
   {
      if( (player->input_js1v->axis.value > 0.7f) && 
          (s->state.activity == k_skate_activity_ground) &&
          (s->state.jump_charge <= 0.01f) )
         s->state.manual_direction = reverse_dir;
   }
   else
   {
      if( player->input_js1v->axis.value < 0.1f )
      {
         s->state.manual_direction = 0;
      }
      else
      {
         if( reverse_dir != s->state.manual_direction )
         {
            return;
         }
      }
   }

   if( s->state.manual_direction )
   {
      float amt = vg_minf( player->input_js1v->axis.value * 8.0f, 1.0f );
      s->weight_distribution[2] = k_board_length * amt * 
                                          (float)s->state.manual_direction;
   }

   /* TODO: Fall back on land normal */
   /* TODO: Lerp weight distribution */
   if( s->state.manual_direction )
   {
      v3f plane_z;

      m3x3_mulv( player->rb.to_world, s->weight_distribution, plane_z );
      v3_negate( plane_z, plane_z );

      v3_muladds( plane_z, s->surface_picture,
                  -v3_dot( plane_z, s->surface_picture ), plane_z );
      v3_normalize( plane_z );

      v3_muladds( plane_z, s->surface_picture, 0.3f, plane_z );
      v3_normalize( plane_z );

      v3f p1;
      v3_muladds( player->rb.co, plane_z, 1.5f, p1 );
      vg_line( player->rb.co, p1, VG__GREEN );

      v3f refdir;
      v3_muls( player->rb.to_world[2], -(float)s->state.manual_direction,
               refdir );

      rb_effect_spring_target_vector( &player->rb, refdir, plane_z,
                                       k_manul_spring, k_manul_dampener,
                                       s->substep_delta );
   }
}

VG_STATIC void skate_adjust_up_direction( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   if( s->state.activity == k_skate_activity_ground )
   {
      v3f target;
      v3_copy( s->surface_picture, target );

      target[1] += 2.0f * s->surface_picture[1];
      v3_normalize( target );

      v3_lerp( s->state.up_dir, target,
               8.0f * s->substep_delta, s->state.up_dir );
   }
   else if( s->state.activity == k_skate_activity_air )
   {
      v3_lerp( s->state.up_dir, player->rb.to_world[1],
               8.0f * s->substep_delta, s->state.up_dir );
   }
   else
   {
      v3_lerp( s->state.up_dir, player->basis[1],
               12.0f * s->substep_delta, s->state.up_dir );
   }
}

VG_STATIC int skate_point_visible( v3f origin, v3f target )
{
   v3f dir;
   v3_sub( target, origin, dir );
   
   ray_hit ray;
   ray.dist = v3_length( dir );
   v3_muls( dir, 1.0f/ray.dist, dir );
   ray.dist -= 0.025f;

   if( ray_world( get_active_world(), origin, dir, &ray ) )
      return 0;

   return 1;
}

VG_STATIC void skate_grind_orient( struct grind_info *inf, m3x3f mtx )
{
   /* TODO: Is N and Dir really orthogonal? */
   v3_copy( inf->dir, mtx[0] );
   v3_copy( inf->n, mtx[1] );
   v3_cross( mtx[0], mtx[1], mtx[2] );
}

VG_STATIC void skate_grind_friction( player_instance *player,
                                     struct grind_info *inf, float strength )
{
   v3f v2;
   v3_muladds( player->rb.to_world[2], inf->n, 
               -v3_dot( player->rb.to_world[2], inf->n ), v2 );

   float a        = 1.0f-fabsf( v3_dot( v2, inf->dir ) ),
         dir      = vg_signf( v3_dot( player->rb.v, inf->dir ) ),
         F        = a * -dir * k_grind_max_friction;

   v3_muladds( player->rb.v, inf->dir, F*k_rb_delta*strength, player->rb.v );
}

VG_STATIC void skate_grind_decay( player_instance *player,
                                  struct grind_info *inf, float strength )
{
   m3x3f mtx, mtx_inv;
   skate_grind_orient( inf, mtx );
   m3x3_transpose( mtx, mtx_inv );

   v3f v_grind;
   m3x3_mulv( mtx_inv, player->rb.v, v_grind );

   float decay = 1.0f - ( k_rb_delta * k_grind_decayxy * strength );
   v3_mul( v_grind, (v3f){ 1.0f, decay, decay }, v_grind );
   m3x3_mulv( mtx, v_grind, player->rb.v );
}

VG_STATIC void skate_grind_truck_apply( player_instance *player,
                                        float sign, struct grind_info *inf,
                                        float strength )
{
   struct player_skate *s = &player->_skate;

   /* TODO: Trash compactor this */
   v3f ra = { 0.0f, -k_board_radius, sign * k_board_length };
   v3f raw, wsp;
   m3x3_mulv( player->rb.to_world, ra, raw );
   v3_add( player->rb.co, raw, wsp );

   v3_copy( ra, s->weight_distribution );

   v3f delta;
   v3_sub( inf->co, wsp, delta );

   /* spring force */
   v3_muladds( player->rb.v, delta, k_spring_force*strength*k_rb_delta, 
               player->rb.v );

   skate_grind_decay( player, inf, strength );
   skate_grind_friction( player, inf, strength );

   /* yeah yeah yeah yeah */
   v3f raw_nplane, axis;
   v3_muladds( raw, inf->n, -v3_dot( inf->n, raw ), raw_nplane );
   v3_cross( raw_nplane, inf->n, axis );
   v3_normalize( axis );

   /* orientation */
   m3x3f mtx;
   skate_grind_orient( inf, mtx );
   v3f target_fwd, fwd, up, target_up;
   m3x3_mulv( mtx, s->grind_vec, target_fwd );
   v3_copy( raw_nplane, fwd );
   v3_copy( player->rb.to_world[1], up );
   v3_copy( inf->n, target_up );

   v3_muladds( target_fwd, inf->n, -v3_dot(inf->n,target_fwd), target_fwd );
   v3_muladds( fwd, inf->n, -v3_dot(inf->n,fwd), fwd );

   v3_normalize( target_fwd );
   v3_normalize( fwd );


   float way = player->input_js1v->axis.value *
                  vg_signf( v3_dot( raw_nplane, player->rb.v ) );

   v4f q;
   q_axis_angle( q, axis, VG_PIf*0.125f * way );
   q_mulv( q, target_up,  target_up );
   q_mulv( q, target_fwd, target_fwd );

   rb_effect_spring_target_vector( &player->rb, up, target_up,
                                    k_grind_spring, 
                                    k_grind_dampener,
                                    k_rb_delta );

   rb_effect_spring_target_vector( &player->rb, fwd, target_fwd,
                                    k_grind_spring*strength, 
                                    k_grind_dampener*strength,
                                    k_rb_delta );

   vg_line_arrow( player->rb.co, target_up, 1.0f, VG__GREEN );
   vg_line_arrow( player->rb.co, fwd, 0.8f, VG__RED );
   vg_line_arrow( player->rb.co, target_fwd, 1.0f, VG__YELOW );

   s->grind_strength = strength;

   /* Fake contact */
   struct grind_limit *limit = &s->limits[ s->limit_count ++ ];
   m4x3_mulv( player->rb.to_local, wsp, limit->ra );
   m3x3_mulv( player->rb.to_local, inf->n, limit->n );
   limit->p = 0.0f;

   v3_copy( inf->dir, s->grind_dir );
}

VG_STATIC void skate_5050_apply( player_instance *player, 
                                 struct grind_info *inf_front,
                                 struct grind_info *inf_back )
{
   struct player_skate *s = &player->_skate;
   struct grind_info inf_avg;

   v3_sub( inf_front->co, inf_back->co, inf_avg.dir );
   v3_muladds( inf_back->co, inf_avg.dir, 0.5f, inf_avg.co );
   v3_normalize( inf_avg.dir );

   v3f axis_front, axis_back, axis;
   v3_cross( inf_front->dir, inf_front->n, axis_front );
   v3_cross( inf_back->dir,  inf_back->n,  axis_back  );
   v3_add( axis_front, axis_back, axis );
   v3_normalize( axis );

   v3_cross( axis, inf_avg.dir, inf_avg.n );
   
   skate_grind_decay( player, &inf_avg, 1.0f );


   float way = player->input_js1v->axis.value *
                  vg_signf( v3_dot( player->rb.to_world[2], player->rb.v ) );
   v4f q;
   v3f up, target_up;
   v3_copy( player->rb.to_world[1], up );
   v3_copy( inf_avg.n, target_up );
   q_axis_angle( q, player->rb.to_world[0], VG_PIf*0.25f * -way );
   q_mulv( q, target_up,  target_up );

   v3_zero( s->weight_distribution );
   s->weight_distribution[2] = k_board_length * -way;

   rb_effect_spring_target_vector( &player->rb, up, target_up,
                                    k_grind_spring, 
                                    k_grind_dampener,
                                    k_rb_delta );

   v3f fwd_nplane, dir_nplane;
   v3_muladds( player->rb.to_world[2], inf_avg.n,
               -v3_dot( player->rb.to_world[2], inf_avg.n ), fwd_nplane );

   v3f dir;
   v3_muls( inf_avg.dir, v3_dot( fwd_nplane, inf_avg.dir ), dir );
   v3_muladds( dir, inf_avg.n, -v3_dot( dir, inf_avg.n ), dir_nplane );

   v3_normalize( fwd_nplane );
   v3_normalize( dir_nplane );

   rb_effect_spring_target_vector( &player->rb, fwd_nplane, dir_nplane,
                                    1000.0f,
                                    k_grind_dampener,
                                    k_rb_delta );

   v3f pos_front = { 0.0f, -k_board_radius, -1.0f * k_board_length },
       pos_back  = { 0.0f, -k_board_radius,  1.0f * k_board_length },
       delta_front, delta_back, delta_total;

   m4x3_mulv( player->rb.to_world, pos_front, pos_front );
   m4x3_mulv( player->rb.to_world, pos_back,  pos_back  );

   v3_sub( inf_front->co, pos_front, delta_front );
   v3_sub( inf_back->co,  pos_back, delta_back );
   v3_add( delta_front, delta_back, delta_total );

   v3_muladds( player->rb.v, delta_total, 50.0f * k_rb_delta, player->rb.v );

   /* Fake contact */
   struct grind_limit *limit = &s->limits[ s->limit_count ++ ];
   v3_zero( limit->ra );
   m3x3_mulv( player->rb.to_local, inf_avg.n, limit->n );
   limit->p = 0.0f;

   v3_copy( inf_avg.dir, s->grind_dir );
}

VG_STATIC int skate_grind_truck_renew( player_instance *player, float sign,
                                       struct grind_info *inf )
{
   struct player_skate *s = &player->_skate;

   v3f wheel_co = { 0.0f, 0.0f,            sign * k_board_length },
       grind_co = { 0.0f, -k_board_radius, sign * k_board_length };

   m4x3_mulv( player->rb.to_world, wheel_co, wheel_co );
   m4x3_mulv( player->rb.to_world, grind_co, grind_co );

   /* Exit condition: lost grind tracking */
   if( !skate_grind_scansq( player, grind_co, player->rb.v, 0.3f, inf ) )
      return 0;

   /* Exit condition: cant see grind target directly */
   if( !skate_point_visible( wheel_co, inf->co ) )
      return 0;

   /* Exit condition: minimum velocity not reached, but allow a bit of error */
   float dv   = fabsf(v3_dot( player->rb.v, inf->dir )),
         minv = k_grind_axel_min_vel*0.8f;

   if( dv < minv )
      return 0;

   if( fabsf(v3_dot( inf->dir, s->grind_dir )) < k_grind_max_edge_angle )
      return 0;

   v3_copy( inf->dir, s->grind_dir );
   return 1;
}

VG_STATIC int skate_grind_truck_entry( player_instance *player, float sign,
                                       struct grind_info *inf )
{
   struct player_skate *s = &player->_skate;

   /* TODO: Trash compactor this */
   v3f ra = { 0.0f, -k_board_radius, sign * k_board_length };

   v3f raw, wsp;
   m3x3_mulv( player->rb.to_world, ra, raw );
   v3_add( player->rb.co, raw, wsp );

   if( skate_grind_scansq( player, wsp, player->rb.v, 0.3, inf ) )
   {
      if( fabsf(v3_dot( player->rb.v, inf->dir )) < k_grind_axel_min_vel )
         return 0;

      /* velocity should be at least 60% aligned */
      v3f pv, axis;
      v3_cross( inf->n, inf->dir, axis );
      v3_muladds( player->rb.v, inf->n, -v3_dot( player->rb.v, inf->n ), pv );
      
      if( v3_length2( pv ) < 0.0001f )
         return 0;
      v3_normalize( pv );

      if( fabsf(v3_dot( pv, inf->dir )) < k_grind_axel_max_angle )
         return 0;

      if( v3_dot( player->rb.v, inf->n ) > 0.5f )
         return 0;

#if 0
      /* check for vertical alignment */
      if( v3_dot( player->rb.to_world[1], inf->n ) < k_grind_axel_max_vangle )
         return 0;
#endif
      
      v3f local_co, local_dir, local_n;
      m4x3_mulv( player->rb.to_local, inf->co,  local_co );
      m3x3_mulv( player->rb.to_local, inf->dir, local_dir );
      m3x3_mulv( player->rb.to_local, inf->n,   local_n );

      v2f delta = { local_co[0], local_co[2] - k_board_length*sign };

      float truck_height = -(k_board_radius+0.03f);

      v3f rv;
      v3_cross( player->rb.w, raw, rv );
      v3_add( player->rb.v, rv, rv );

      if( (local_co[1] >= truck_height) &&
          (v2_length2( delta ) <= k_board_radius*k_board_radius) )
      {
         return 1;
      }
   }

   return 0;
}

VG_STATIC void skate_boardslide_apply( player_instance *player,
                                       struct grind_info *inf )
{
   struct player_skate *s = &player->_skate;

   v3f local_co, local_dir, local_n;
   m4x3_mulv( player->rb.to_local, inf->co, local_co );
   m3x3_mulv( player->rb.to_local, inf->dir, local_dir );
   m3x3_mulv( player->rb.to_local, inf->n, local_n );

   v3f intersection;
   v3_muladds( local_co, local_dir, local_co[0]/-local_dir[0], 
               intersection );
   v3_copy( intersection, s->weight_distribution );

   skate_grind_decay( player, inf, 0.1f );
   skate_grind_friction( player, inf, 0.25f );

   /* direction alignment */
   v3f dir, perp;
   v3_cross( local_dir, local_n, perp );
   v3_muls( local_dir, vg_signf(local_dir[0]), dir );
   v3_muls( perp, vg_signf(perp[2]), perp );

   m3x3_mulv( player->rb.to_world, dir, dir );
   m3x3_mulv( player->rb.to_world, perp, perp );

   rb_effect_spring_target_vector( &player->rb, player->rb.to_world[0],
                                    dir, 
                                    k_grind_spring, k_grind_dampener,
                                    k_rb_delta );

   rb_effect_spring_target_vector( &player->rb, player->rb.to_world[2],
                                    perp,
                                    k_grind_spring, k_grind_dampener,
                                    k_rb_delta );

   vg_line_arrow( player->rb.co, dir, 0.5f, VG__GREEN );
   vg_line_arrow( player->rb.co, perp, 0.5f, VG__BLUE );

   v3_copy( inf->dir, s->grind_dir );
}

VG_STATIC int skate_boardslide_entry( player_instance *player,
                                      struct grind_info *inf )
{
   struct player_skate *s = &player->_skate;

   if( skate_grind_scansq( player, player->rb.co, 
                           player->rb.to_world[0], k_board_length,
                           inf ) )
   {
      v3f local_co, local_dir;
      m4x3_mulv( player->rb.to_local, inf->co, local_co );
      m3x3_mulv( player->rb.to_local, inf->dir, local_dir );

      if( (fabsf(local_co[2]) <= k_board_length) &&   /* within wood area */
          (local_co[1] >= 0.0f) &&                    /* at deck level */
          (fabsf(local_dir[0]) >= 0.5f) )             /* perpendicular to us */
      {
         if( fabsf(v3_dot( player->rb.v, inf->dir )) < k_grind_axel_min_vel )
            return 0;

         return 1;
      }
   }

   return 0;
}

VG_STATIC int skate_boardslide_renew( player_instance *player,
                                      struct grind_info *inf )
{
   struct player_skate *s = &player->_skate;

   if( !skate_grind_scansq( player, player->rb.co, 
                            player->rb.to_world[0], k_board_length,
                            inf ) )
      return 0;

   /* Exit condition: cant see grind target directly */
   v3f vis;
   v3_muladds( player->rb.co, player->rb.to_world[1], 0.2f, vis );
   if( !skate_point_visible( vis, inf->co ) )
      return 0;

   /* Exit condition: minimum velocity not reached, but allow a bit of error 
    * TODO: trash compactor */
   float dv   = fabsf(v3_dot( player->rb.v, inf->dir )),
         minv = k_grind_axel_min_vel*0.8f;

   if( dv < minv )
      return 0;

   if( fabsf(v3_dot( inf->dir, s->grind_dir )) < k_grind_max_edge_angle )
      return 0;

   return 1;
}

VG_STATIC void skate_store_grind_vec( player_instance *player,
                                      struct grind_info *inf )
{
   struct player_skate *s = &player->_skate;

   m3x3f mtx;
   skate_grind_orient( inf, mtx );
   m3x3_transpose( mtx, mtx );

   v3f raw;
   v3_sub( inf->co, player->rb.co, raw );

   m3x3_mulv( mtx, raw, s->grind_vec );
   v3_normalize( s->grind_vec );
   v3_copy( inf->dir, s->grind_dir );
}

VG_STATIC enum skate_activity skate_availible_grind( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   /* debounces this state manager a little bit */
   if( s->frames_since_activity_change < 10 )
   {
      s->frames_since_activity_change ++;
      return k_skate_activity_undefined;
   }

   struct grind_info inf_back50,
                     inf_front50,
                     inf_slide;

   int res_back50  = 0,
       res_front50 = 0,
       res_slide   = 0;

   if( s->state.activity == k_skate_activity_grind_boardslide )
   {
      res_slide = skate_boardslide_renew( player, &inf_slide );
   }
   else if( s->state.activity == k_skate_activity_grind_back50 )
   {
      res_back50  = skate_grind_truck_renew( player,  1.0f, &inf_back50 );
      res_front50 = skate_grind_truck_entry( player, -1.0f, &inf_front50 );
   }
   else if( s->state.activity == k_skate_activity_grind_front50 )
   {
      res_front50 = skate_grind_truck_renew( player, -1.0f, &inf_front50 );
      res_back50  = skate_grind_truck_entry( player,  1.0f, &inf_back50 );
   }
   else if( s->state.activity == k_skate_activity_grind_5050 )
   {
      res_front50 = skate_grind_truck_renew( player, -1.0f, &inf_front50 );
      res_back50  = skate_grind_truck_entry( player,  1.0f, &inf_back50 );
   }
   else
   {
      res_slide   = skate_boardslide_entry( player, &inf_slide );
      res_back50  = skate_grind_truck_entry( player,  1.0f, &inf_back50 );
      res_front50 = skate_grind_truck_entry( player, -1.0f, &inf_front50 );

      if( res_back50 != res_front50 )
      {
         int wants_to_do_that = fabsf(player->input_js1v->axis.value) >= 0.25f;

         res_back50  &= wants_to_do_that;
         res_front50 &= wants_to_do_that;
      }
   }

   const enum skate_activity table[] =
   {                                      /* slide | back | front */
      k_skate_activity_undefined,         /* 0       0      0     */
      k_skate_activity_grind_front50,     /* 0       0      1     */
      k_skate_activity_grind_back50,      /* 0       1      0     */
      k_skate_activity_grind_5050,        /* 0       1      1     */

      /* slide has priority always */
      k_skate_activity_grind_boardslide,  /* 1       0      0     */
      k_skate_activity_grind_boardslide,  /* 1       0      1     */
      k_skate_activity_grind_boardslide,  /* 1       1      0     */
      k_skate_activity_grind_boardslide,  /* 1       1      1     */
   }
   , new_activity = table[ res_slide << 2 | res_back50 << 1 | res_front50 ];

   if(      new_activity == k_skate_activity_undefined )
   {
      if( s->state.activity >= k_skate_activity_grind_any )
         s->frames_since_activity_change = 0;
   }
   else if( new_activity == k_skate_activity_grind_boardslide )
   {
      skate_boardslide_apply( player, &inf_slide );
   }
   else if( new_activity == k_skate_activity_grind_back50 )
   {
      if( s->state.activity != k_skate_activity_grind_back50 )
         skate_store_grind_vec( player, &inf_back50 );

      skate_grind_truck_apply( player,  1.0f, &inf_back50, 1.0f );
   }
   else if( new_activity == k_skate_activity_grind_front50 )
   {
      if( s->state.activity != k_skate_activity_grind_front50 )
         skate_store_grind_vec( player, &inf_front50 );

      skate_grind_truck_apply( player, -1.0f, &inf_front50, 1.0f );
   }
   else if( new_activity == k_skate_activity_grind_5050 )
      skate_5050_apply( player, &inf_front50, &inf_back50 );

   return new_activity;
}

VG_STATIC void player__skate_update( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   world_instance *world = get_active_world();

   v3_copy( player->rb.co, s->state.prev_pos );
   s->state.activity_prev = s->state.activity;

   struct board_collider
   {
      v3f   pos;
      float radius;

      u32   colour;

      enum  board_collider_state
      {
         k_collider_state_default,
         k_collider_state_disabled,
         k_collider_state_colliding
      }
      state;
   }
   wheels[] =
   {
      { 
         { 0.0f, 0.0f,    -k_board_length }, 
         .radius = k_board_radius,
         .colour = VG__RED
      },
      { 
         { 0.0f, 0.0f,     k_board_length }, 
         .radius = k_board_radius,
         .colour = VG__GREEN
      }
   };

   const int k_wheel_count = 2;

   s->substep = k_rb_delta;
   s->substep_delta = s->substep;
   s->limit_count = 0;

   int substep_count = 0;

   v3_zero( s->surface_picture );

   for( int i=0; i<k_wheel_count; i++ )
      wheels[i].state = k_collider_state_default;

   /* check if we can enter or continue grind */
   enum skate_activity grindable_activity = skate_availible_grind( player );
   if( grindable_activity != k_skate_activity_undefined )
   {
      s->state.activity = grindable_activity;
      goto grinding;
   }

   int contact_count = 0;
   for( int i=0; i<2; i++ )
   {
      v3f normal, axel;
      v3_copy( player->rb.to_world[0], axel );

      if( skate_compute_surface_alignment( player, wheels[i].pos, 
                                           wheels[i].colour, normal, axel ) )
      {
         rb_effect_spring_target_vector( &player->rb, player->rb.to_world[0],
                                          axel,
                                          k_surface_spring, k_surface_dampener,
                                          s->substep_delta );

         v3_add( normal, s->surface_picture, s->surface_picture );
         contact_count ++;
      }

      m3x3_mulv( player->rb.to_local, axel, s->truckv0[i] );
   }

   if( contact_count )
   {
      s->state.activity = k_skate_activity_ground;
      s->state.gravity_bias = k_gravity;
      v3_normalize( s->surface_picture );

      skate_apply_friction_model( player );
      skate_weight_distribute( player );
   }
   else
   {
      s->state.activity = k_skate_activity_air;
      v3_zero( s->weight_distribution );
      skate_apply_air_model( player );
   }

grinding:;

   if( s->state.activity == k_skate_activity_grind_back50 )
      wheels[1].state = k_collider_state_disabled;
   if( s->state.activity == k_skate_activity_grind_front50 )
      wheels[0].state = k_collider_state_disabled;
   if( s->state.activity == k_skate_activity_grind_5050 )
   {
      wheels[0].state = k_collider_state_disabled;
      wheels[1].state = k_collider_state_disabled;
   }

   /* all activities */
   skate_apply_steering_model( player );
   skate_adjust_up_direction( player );
   skate_apply_cog_model( player );
   skate_apply_jump_model( player );
   skate_apply_grab_model( player );
   skate_apply_trick_model( player );
   skate_apply_pump_model( player );

begin_collision:;

   /*
    * Phase 0: Continous collision detection
    * --------------------------------------------------------------------------
    */

   v3f head_wp0, head_wp1, start_co;
   m4x3_mulv( player->rb.to_world, s->state.head_position, head_wp0 );
   v3_copy( player->rb.co, start_co );

   /* calculate transform one step into future */
   v3f future_co;
   v4f future_q;
   v3_muladds( player->rb.co, player->rb.v, s->substep, future_co );

   if( v3_length2( player->rb.w ) > 0.0f )
   {
      v4f rotation;
      v3f axis;
      v3_copy( player->rb.w, axis );
      
      float mag = v3_length( axis );
      v3_divs( axis, mag, axis );
      q_axis_angle( rotation, axis, mag*s->substep );
      q_mul( rotation, player->rb.q, future_q );
      q_normalize( future_q );
   }
   else
      v4_copy( player->rb.q, future_q );

   v3f future_cg, current_cg, cg_offset;
   q_mulv( player->rb.q, s->weight_distribution, current_cg );
   q_mulv( future_q, s->weight_distribution, future_cg );
   v3_sub( future_cg, current_cg, cg_offset );

   /* calculate the minimum time we can move */
   float max_time = s->substep;

   for( int i=0; i<k_wheel_count; i++ )
   {
      if( wheels[i].state == k_collider_state_disabled )
         continue;

      v3f current, future, r_cg;
      
      q_mulv( future_q, wheels[i].pos, future );
      v3_add( future, future_co, future );
      v3_add( cg_offset, future, future );

      q_mulv( player->rb.q, wheels[i].pos, current );
      v3_add( current, player->rb.co, current );
      
      float t;
      v3f n;

      float cast_radius = wheels[i].radius - k_penetration_slop * 2.0f;
      if( spherecast_world( world, current, future, cast_radius, &t, n ) != -1)
         max_time = vg_minf( max_time, t * s->substep );
   }

   /* clamp to a fraction of delta, to prevent locking */
   float rate_lock = substep_count;
   rate_lock *= k_rb_delta * 0.1f;
   rate_lock *= rate_lock;

   max_time = vg_maxf( max_time, rate_lock );
   s->substep_delta = max_time;

   /* integrate */
   v3_muladds( player->rb.co, player->rb.v, s->substep_delta, player->rb.co );
   if( v3_length2( player->rb.w ) > 0.0f )
   {
      v4f rotation;
      v3f axis;
      v3_copy( player->rb.w, axis );
      
      float mag = v3_length( axis );
      v3_divs( axis, mag, axis );
      q_axis_angle( rotation, axis, mag*s->substep_delta );
      q_mul( rotation, player->rb.q, player->rb.q );
      q_normalize( player->rb.q );

      q_mulv( player->rb.q, s->weight_distribution, future_cg );
      v3_sub( current_cg, future_cg, cg_offset );
      v3_add( player->rb.co, cg_offset, player->rb.co );
   }

   rb_update_transform( &player->rb );
   v3_muladds( player->rb.v, player->basis[1],
               -s->state.gravity_bias * s->substep_delta, player->rb.v );

   s->substep -= s->substep_delta;

   rb_ct manifold[128];
   int manifold_len   = 0;

   /*
    * Phase -1: head detection
    * --------------------------------------------------------------------------
    */
   m4x3_mulv( player->rb.to_world, s->state.head_position, head_wp1 );

   float t;
   v3f n;
   if( (v3_dist2( head_wp0, head_wp1 ) > 0.001f) &&
       (spherecast_world( world, head_wp0, head_wp1, 0.2f, &t, n ) != -1) )
   {
      v3_lerp( start_co, player->rb.co, t, player->rb.co );
      rb_update_transform( &player->rb );

      player__skate_kill_audio( player );
      player__dead_transition( player );
      return;
   }

   /*
    * Phase 1: Regular collision detection
    * --------------------------------------------------------------------------
    */

   for( int i=0; i<k_wheel_count; i++ )
   {
      if( wheels[i].state == k_collider_state_disabled )
         continue;

      m4x3f mtx;
      m3x3_identity( mtx );
      m4x3_mulv( player->rb.to_world, wheels[i].pos, mtx[3] );
      
      rb_sphere collider = { .radius = wheels[i].radius };

      rb_ct *man = &manifold[ manifold_len ];

      int l = skate_collide_smooth( player, mtx, &collider, man );
      if( l )
         wheels[i].state = k_collider_state_colliding;

      manifold_len += l;
   }

   float grind_radius = k_board_radius * 0.75f;
   rb_capsule capsule = { .height = (k_board_length+0.2f)*2.0f, 
                          .radius=grind_radius };
   m4x3f mtx;
   v3_muls( player->rb.to_world[0],  1.0f, mtx[0] );
   v3_muls( player->rb.to_world[2], -1.0f, mtx[1] );
   v3_muls( player->rb.to_world[1],  1.0f, mtx[2] );
   v3_muladds( player->rb.to_world[3], player->rb.to_world[1], 
               grind_radius + k_board_radius*0.25f, mtx[3] );

   rb_ct *cman = &manifold[manifold_len];

   int l = rb_capsule__scene( mtx, &capsule, NULL, &world->rb_geo.inf.scene,
                              cman );

   /* weld joints */
   for( int i=0; i<l; i ++ )
      cman[l].type = k_contact_type_edge;
   rb_manifold_filter_joint_edges( cman, l, 0.03f );
   l = rb_manifold_apply_filtered( cman, l );

   manifold_len += l;

   debug_capsule( mtx, capsule.radius, capsule.height, VG__WHITE );

   /* add limits */
   for( int i=0; i<s->limit_count; i++ )
   {
      struct grind_limit *limit = &s->limits[i];
      rb_ct *ct = &manifold[ manifold_len ++ ];
      m4x3_mulv( player->rb.to_world, limit->ra, ct->co );
      m3x3_mulv( player->rb.to_world, limit->n, ct->n );
      ct->p = limit->p;
      ct->type = k_contact_type_default;
   }

   /* 
    * Phase 3: Dynamics
    * --------------------------------------------------------------------------
    */


   v3f world_cog;
   m4x3_mulv( player->rb.to_world, s->weight_distribution, world_cog );
   vg_line_pt3( world_cog, 0.02f, VG__BLACK );

   for( int i=0; i<manifold_len; i ++ )
   {
      rb_prepare_contact( &manifold[i], s->substep_delta );
      rb_debug_contact( &manifold[i] );
   }

   /* yes, we are currently rebuilding mass matrices every frame. too bad! */
   v3f extent = { k_board_width, 0.1f, k_board_length };
   float ex2 = k_board_interia*extent[0]*extent[0],
         ey2 = k_board_interia*extent[1]*extent[1],
         ez2 = k_board_interia*extent[2]*extent[2];

   float mass = 2.0f * (extent[0]*extent[1]*extent[2]);
   float inv_mass = 1.0f/mass;

   v3f I;
   I[0] = ((1.0f/12.0f) * mass * (ey2+ez2));
   I[1] = ((1.0f/12.0f) * mass * (ex2+ez2));
   I[2] = ((1.0f/12.0f) * mass * (ex2+ey2));

   m3x3f iI;
   m3x3_identity( iI );
   iI[0][0] = I[0];
   iI[1][1] = I[1];
   iI[2][2] = I[2];
   m3x3_inv( iI, iI );

   m3x3f iIw;
   m3x3_mul( iI, player->rb.to_local, iIw );
   m3x3_mul( player->rb.to_world, iIw, iIw );

   for( int j=0; j<10; j++ )
   {
      for( int i=0; i<manifold_len; i++ )
      {
         /* 
          * regular dance; calculate velocity & total mass, apply impulse.
          */

         struct contact *ct = &manifold[i];
         
         v3f rv, delta;
         v3_sub( ct->co, world_cog, delta ); 
         v3_cross( player->rb.w, delta, rv );
         v3_add( player->rb.v, rv, rv );

         v3f raCn;
         v3_cross( delta, ct->n, raCn );

         v3f raCnI, rbCnI;
         m3x3_mulv( iIw, raCn, raCnI );

         float normal_mass = 1.0f / (inv_mass + v3_dot(raCn,raCnI)),
               vn = v3_dot( rv, ct->n ),
               lambda = normal_mass * ( -vn );

         float temp = ct->norm_impulse;
         ct->norm_impulse = vg_maxf( temp + lambda, 0.0f );
         lambda = ct->norm_impulse - temp;

         v3f impulse;
         v3_muls( ct->n, lambda, impulse );

         v3_muladds( player->rb.v, impulse, inv_mass, player->rb.v );
         v3_cross( delta, impulse, impulse );
         m3x3_mulv( iIw, impulse, impulse );
         v3_add( impulse, player->rb.w, player->rb.w );

         v3_cross( player->rb.w, delta, rv );
         v3_add( player->rb.v, rv, rv );
         vn = v3_dot( rv, ct->n );
      }
   }

   v3f dt;
   rb_depenetrate( manifold, manifold_len, dt );
   v3_add( dt, player->rb.co, player->rb.co );
   rb_update_transform( &player->rb );

   substep_count ++;

   if( s->substep >= 0.0001f )
      goto begin_collision;      /* again! */

   /* 
    * End of collision and dynamics routine
    * --------------------------------------------------------------------------
    */

   s->surface = k_surface_prop_concrete;

   for( int i=0; i<manifold_len; i++ ){
      rb_ct *ct = &manifold[i];
      struct world_surface *surf = world_contact_surface( world, ct );

      if( surf->info.surface_prop != k_surface_prop_concrete )
         s->surface = surf->info.surface_prop;
   }

   for( int i=0; i<k_wheel_count; i++ ){
      m4x3f mtx;
      m3x3_copy( player->rb.to_world, mtx );
      m4x3_mulv( player->rb.to_world, wheels[i].pos, mtx[3] );
      debug_sphere( mtx, wheels[i].radius,
                   (u32[]){ VG__WHITE, VG__BLACK, 
                            wheels[i].colour }[ wheels[i].state ]);
   }

   skate_integrate( player );
   vg_line_pt3( s->state.cog, 0.02f, VG__WHITE );

   ent_gate *gate = 
      world_intersect_gates(world, player->rb.co, s->state.prev_pos );

   if( gate ){
      m4x3_mulv( gate->transport, player->rb.co, player->rb.co );
      m3x3_mulv( gate->transport, player->rb.v,  player->rb.v );
      m4x3_mulv( gate->transport, s->state.cog,   s->state.cog );
      m3x3_mulv( gate->transport, s->state.cog_v, s->state.cog_v );
      m3x3_mulv( gate->transport, s->state.throw_v, s->state.throw_v );
      m3x3_mulv( gate->transport, s->state.head_position,
                                  s->state.head_position );
      m3x3_mulv( gate->transport, s->state.up_dir, s->state.up_dir );

      v4f transport_rotation;
      m3x3_q( gate->transport, transport_rotation );
      q_mul( transport_rotation, player->rb.q, player->rb.q );
      rb_update_transform( &player->rb );

      s->state_gate_storage = s->state;
      player__pass_gate( player, gate );
   }

   /* FIXME: Rate limit */
   static int stick_frames = 0;

   if( s->state.activity == k_skate_activity_ground )
      stick_frames ++;
   else
      stick_frames = 0;


   if( stick_frames == 4 )
   {
      audio_lock();
      if( (fabsf(s->state.slip) > 0.75f) )
      {
         audio_oneshot_3d( &audio_lands[rand()%2+3], player->rb.co, 
                           40.0f, 1.0f );
      }
      else
      {
         audio_oneshot_3d( &audio_lands[rand()%3], player->rb.co, 
                           40.0f, 1.0f );
      }
      audio_unlock();
   }
}

VG_STATIC void player__skate_im_gui( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   player__debugtext( 1, "V:  %5.2f %5.2f %5.2f",player->rb.v[0],
                                                player->rb.v[1],
                                                player->rb.v[2] );
   player__debugtext( 1, "CO: %5.2f %5.2f %5.2f",player->rb.co[0],
                                                player->rb.co[1],
                                                player->rb.co[2] );
   player__debugtext( 1, "W:  %5.2f %5.2f %5.2f",player->rb.w[0],
                                                player->rb.w[1],
                                                player->rb.w[2] );

   const char *activity_txt[] = 
   {
      "air",
      "ground",
      "undefined (INVALID)",
      "grind_any (INVALID)",
      "grind_boardslide",
      "grind_noseslide",
      "grind_tailslide",
      "grind_back50",
      "grind_front50",
      "grind_5050"
   };

   player__debugtext( 1, "activity: %s", activity_txt[s->state.activity] );
#if 0
   player__debugtext( 1, "steer_s: %5.2f %5.2f [%.2f %.2f]",
                        s->state.steerx_s, s->state.steery_s,
                        k_steer_ground, k_steer_air );
#endif
   player__debugtext( 1, "flip: %.4f %.4f", s->state.flip_rate, 
                                             s->state.flip_time );
   player__debugtext( 1, "trickv: %.2f %.2f %.2f", 
                           s->state.trick_vel[0],
                           s->state.trick_vel[1],
                           s->state.trick_vel[2] );
   player__debugtext( 1, "tricke: %.2f %.2f %.2f", 
                           s->state.trick_euler[0],
                           s->state.trick_euler[1],
                           s->state.trick_euler[2] );
}

VG_STATIC void player__skate_animate( player_instance *player,
                                     player_animation *dest )
{
   struct player_skate *s = &player->_skate;
   struct player_avatar *av = player->playeravatar;
   struct skeleton *sk = &av->sk;

   /* Head */
   float kheight = 2.0f,
         kleg = 0.6f;

   v3f offset;
   v3_zero( offset );

   v3f cog_local, cog_ideal;
   m4x3_mulv( player->rb.to_local, s->state.cog, cog_local );

   v3_copy( s->state.up_dir, cog_ideal );
   v3_normalize( cog_ideal );
   m3x3_mulv( player->rb.to_local, cog_ideal, cog_ideal );

   v3_sub( cog_ideal, cog_local, offset );


   v3_muls( offset, 4.0f, offset );
   offset[1] *= -1.0f;

   float curspeed  = v3_length( player->rb.v ),
         kickspeed = vg_clampf( curspeed*(1.0f/40.0f), 0.0f, 1.0f ),
         kicks     = (vg_randf()-0.5f)*2.0f*kickspeed,
         sign      = vg_signf( kicks );

   s->wobble[0] = vg_lerpf( s->wobble[0], kicks*kicks*sign, 6.0f*vg.time_delta);
   s->wobble[1] = vg_lerpf( s->wobble[1], s->wobble[0],     2.4f*vg.time_delta);

   offset[0] *= 0.26f;
   offset[0] += s->wobble[1]*3.0f;

   offset[1] *= -0.3f;
   offset[2] *= 0.01f;

   offset[0]=vg_clampf(offset[0],-0.8f,0.8f)*(1.0f-fabsf(s->blend_slide)*0.9f);
   offset[1]=vg_clampf(offset[1],-0.5f,0.0f);

   /* 
    * Animation blending
    * ===========================================
    */
   
   /* sliding */
   {
      float desired  = vg_clampf( fabsf( s->state.slip ), 0.0f, 1.0f );
      s->blend_slide = vg_lerpf( s->blend_slide, desired, 2.4f*vg.time_delta);
   }
   
   /* movement information */
   {
      int iair = s->state.activity == k_skate_activity_air;

      float dirz = s->state.reverse > 0.0f? 0.0f: 1.0f,
            dirx = s->state.slip < 0.0f?    0.0f: 1.0f,
            fly  = iair?                    1.0f: 0.0f,
            wdist= s->weight_distribution[2] / k_board_length;

      s->blend_z     = vg_lerpf( s->blend_z,      dirz,  2.4f*vg.time_delta );
      s->blend_x     = vg_lerpf( s->blend_x,      dirx,  0.6f*vg.time_delta );
      s->blend_fly   = vg_lerpf( s->blend_fly,    fly,   2.4f*vg.time_delta );
      s->blend_weight= vg_lerpf( s->blend_weight, wdist, 9.0f*vg.time_delta );
   }

   mdl_keyframe apose[32], bpose[32];
   mdl_keyframe ground_pose[32];
   {
      /* when the player is moving fast he will crouch down a little bit */
      float stand = 1.0f - vg_clampf( curspeed * 0.03f, 0.0f, 1.0f );
      s->blend_stand = vg_lerpf( s->blend_stand, stand, 6.0f*vg.time_delta );

      /* stand/crouch */
      float dir_frame   = s->blend_z * (15.0f/30.0f),
            stand_blend = offset[1]*-2.0f;

      v3f local_cog;
      m4x3_mulv( player->rb.to_local, s->state.cog, local_cog );

      stand_blend = vg_clampf( 1.0f-local_cog[1], 0, 1 );

      skeleton_sample_anim( sk, s->anim_stand, dir_frame, apose );
      skeleton_sample_anim( sk, s->anim_highg, dir_frame, bpose );
      skeleton_lerp_pose( sk, apose, bpose, stand_blend, apose );

      /* sliding */
      float slide_frame = s->blend_x * (15.0f/30.0f);
      skeleton_sample_anim( sk, s->anim_slide, slide_frame, bpose );
      skeleton_lerp_pose( sk, apose, bpose, s->blend_slide, apose );

      /* pushing */
      double push_time = vg.time - s->state.start_push;
      s->blend_push = vg_lerpf( s->blend_push,
                               (vg.time - s->state.cur_push) < 0.125,
                               6.0f*vg.time_delta );

      float pt = push_time + vg.accumulator;
      if( s->state.reverse > 0.0f )
         skeleton_sample_anim( sk, s->anim_push, pt, bpose );
      else
         skeleton_sample_anim( sk, s->anim_push_reverse, pt, bpose );

      skeleton_lerp_pose( sk, apose, bpose, s->blend_push, apose );

      /* trick setup */
      float jump_start_frame = 14.0f/30.0f;

      float charge = s->state.jump_charge;
      s->blend_jump = vg_lerpf( s->blend_jump, charge, 8.4f*vg.time_delta );

      float setup_frame = charge * jump_start_frame,
            setup_blend = vg_minf( s->blend_jump, 1.0f );
      
      float jump_frame = (vg.time - s->state.jump_time) + jump_start_frame;
      if( jump_frame >= jump_start_frame && jump_frame <= (40.0f/30.0f) )
         setup_frame = jump_frame;

      struct skeleton_anim *jump_anim = s->state.jump_dir?
                                        s->anim_ollie:
                                        s->anim_ollie_reverse;

      skeleton_sample_anim_clamped( sk, jump_anim, setup_frame, bpose );
      skeleton_lerp_pose( sk, apose, bpose, setup_blend, ground_pose );
   }
   
   mdl_keyframe air_pose[32];
   {
      float target = -player->input_js1h->axis.value;
      s->blend_airdir = vg_lerpf( s->blend_airdir, target, 2.4f*vg.time_delta );
      
      float air_frame = (s->blend_airdir*0.5f+0.5f) * (15.0f/30.0f);
      skeleton_sample_anim( sk, s->anim_air, air_frame, apose );

      static v2f grab_choice;

      v2f grab_input = { player->input_js2h->axis.value,
                         player->input_js2v->axis.value };
      v2_add( s->state.grab_mouse_delta, grab_input, grab_input );
      if( v2_length2( grab_input ) <= 0.001f )
         grab_input[0] = -1.0f;
      else
         v2_normalize_clamp( grab_input );
      v2_lerp( grab_choice, grab_input, 2.4f*vg.time_delta, grab_choice );

      float ang = atan2f( grab_choice[0], grab_choice[1] ),
            ang_unit = (ang+VG_PIf) * (1.0f/VG_TAUf),
            grab_frame = ang_unit * (15.0f/30.0f);

      skeleton_sample_anim( sk, s->anim_grabs, grab_frame, bpose );
      skeleton_lerp_pose( sk, apose, bpose, s->state.grabbing, air_pose );
   }

   skeleton_lerp_pose( sk, ground_pose, air_pose, s->blend_fly, dest->pose );

   float add_grab_mod = 1.0f - s->blend_fly;

   /* additive effects */
   {
      u32 apply_to[] = { av->id_hip, 
                         av->id_ik_hand_l,
                         av->id_ik_hand_r,
                         av->id_ik_elbow_l,
                         av->id_ik_elbow_r };

      for( int i=0; i<vg_list_size(apply_to); i ++ )
      {
         dest->pose[apply_to[i]-1].co[0] += offset[0]*add_grab_mod;
         dest->pose[apply_to[i]-1].co[2] += offset[2]*add_grab_mod;
      }


      /* angle correction */
      if( v3_length2( s->state.up_dir ) > 0.001f )
      {
         v3f ndir;
         m3x3_mulv( player->rb.to_local, s->state.up_dir, ndir );
         v3_normalize( ndir );

         v3f up = { 0.0f, 1.0f, 0.0f };

         float a = v3_dot( ndir, up );
         a = acosf( vg_clampf( a, -1.0f, 1.0f ) );

         v3f axis;
         v4f q;
         
         v3_cross( up, ndir, axis );
         q_axis_angle( q, axis, a );

         mdl_keyframe *kf_hip = &dest->pose[av->id_hip-1];
         
         for( int i=0; i<vg_list_size(apply_to); i ++ )
         {
            mdl_keyframe *kf = &dest->pose[apply_to[i]-1];

            v3f v0;
            v3_sub( kf->co, kf_hip->co, v0 );
            q_mulv( q, v0, v0 );
            v3_add( v0, kf_hip->co, kf->co );

            q_mul( q, kf->q, kf->q );
            q_normalize( kf->q );
         }

         v3f p1, p2;
         m3x3_mulv( player->rb.to_world, up, p1 );
         m3x3_mulv( player->rb.to_world, ndir, p2 );

         vg_line_arrow( player->rb.co, p1, 0.25f, VG__PINK );
         vg_line_arrow( player->rb.co, p2, 0.25f, VG__PINK );
      }



      mdl_keyframe *kf_board    = &dest->pose[av->id_board-1],
                   *kf_foot_l   = &dest->pose[av->id_ik_foot_l-1],
                   *kf_foot_r   = &dest->pose[av->id_ik_foot_r-1],
                   *kf_wheels[] = { &dest->pose[av->id_wheel_r-1],
                                    &dest->pose[av->id_wheel_l-1] };

      v4f qtotal;
      v4f qtrickr, qyawr, qpitchr, qrollr;
      v3f eulerr;

      v3_muls( s->board_trick_residuald, VG_TAUf, eulerr );

      q_axis_angle( qyawr,   (v3f){0.0f,1.0f,0.0f}, eulerr[0] * 0.5f );
      q_axis_angle( qpitchr, (v3f){1.0f,0.0f,0.0f}, eulerr[1] );
      q_axis_angle( qrollr,  (v3f){0.0f,0.0f,1.0f}, eulerr[2] );

      q_mul( qpitchr, qrollr, qtrickr );
      q_mul( qyawr, qtrickr, qtotal );
      q_normalize( qtotal );

      q_mul( qtotal, kf_board->q, kf_board->q );


      /* trick rotation */
      v4f qtrick, qyaw, qpitch, qroll;
      v3f euler;
      v3_muls( s->state.trick_euler, VG_TAUf, euler );

      q_axis_angle( qyaw,   (v3f){0.0f,1.0f,0.0f}, euler[0] * 0.5f );
      q_axis_angle( qpitch, (v3f){1.0f,0.0f,0.0f}, euler[1] );
      q_axis_angle( qroll,  (v3f){0.0f,0.0f,1.0f}, euler[2] );

      q_mul( qpitch, qroll, qtrick );
      q_mul( qyaw, qtrick, qtrick );
      q_mul( kf_board->q, qtrick, kf_board->q );
      q_normalize( kf_board->q );

      /* foot weight distribution */
      if( s->blend_weight > 0.0f )
      {
         kf_foot_l->co[2] += s->blend_weight * 0.2f;
         kf_foot_r->co[2] += s->blend_weight * 0.1f;
      }
      else
      {
         kf_foot_r->co[2] += s->blend_weight * 0.3f;
         kf_foot_l->co[2] += s->blend_weight * 0.1f;
      }

      /* truck rotation */
      for( int i=0; i<2; i++ )
      {
         float a = vg_minf( s->truckv0[i][0], 1.0f );
         a = -acosf( a ) * vg_signf( s->truckv0[i][1] );

         v4f q;
         q_axis_angle( q, (v3f){0.0f,0.0f,1.0f}, a );
         q_mul( q, kf_wheels[i]->q, kf_wheels[i]->q );
         q_normalize( kf_wheels[i]->q );
      }
   }

   /* transform */
   rb_extrapolate( &player->rb, dest->root_co, dest->root_q );
   v3_muladds( dest->root_co, player->rb.to_world[1], -0.1f, dest->root_co );

   float substep = vg_clampf( vg.accumulator / VG_TIMESTEP_FIXED, 0.0f, 1.0f );

   v4f qflip;
   if( (s->state.activity == k_skate_activity_air) &&
       (fabsf(s->state.flip_rate) > 0.01f) )
   {
      float t     = s->state.flip_time;
            sign  = vg_signf( t );

      t  = 1.0f - vg_minf( 1.0f, fabsf( t * 1.1f ) );
      t  = sign * (1.0f-t*t);

      float angle = vg_clampf( t, -1.0f, 1.0f ) * VG_TAUf,
            distm = s->land_dist * fabsf(s->state.flip_rate) * 3.0f,
            blend = vg_clampf( 1.0f-distm, 0.0f, 1.0f );

      angle = vg_lerpf( angle, vg_signf(s->state.flip_rate) * VG_TAUf, blend );

      q_axis_angle( qflip, s->state.flip_axis, angle );
      q_mul( qflip, dest->root_q, dest->root_q );
      q_normalize( dest->root_q );

      v3f rotation_point, rco;
      v3_muladds( player->rb.co, player->rb.to_world[1], 0.5f, rotation_point );
      v3_sub( dest->root_co, rotation_point, rco );
      
      q_mulv( qflip, rco, rco );
      v3_add( rco, rotation_point, dest->root_co );
   }

   skeleton_copy_pose( sk, dest->pose, player->holdout_pose );
}

VG_STATIC void player__skate_post_animate( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   struct player_avatar *av = player->playeravatar;

   player->cam_velocity_influence = 1.0f;

   v3f head = { 0.0f, 1.8f, 0.0f };
   m4x3_mulv( av->sk.final_mtx[ av->id_head ], head, s->state.head_position );
   m4x3_mulv( player->rb.to_local, s->state.head_position, 
                                   s->state.head_position );
}

VG_STATIC void player__skate_reset_animator( player_instance *player )
{
   struct player_skate *s = &player->_skate;

   if( s->state.activity == k_skate_activity_air )
      s->blend_fly = 1.0f;
   else
      s->blend_fly = 0.0f;

   s->blend_slide = 0.0f;
   s->blend_z = 0.0f;
   s->blend_x = 0.0f;
   s->blend_stand = 0.0f;
   s->blend_push = 0.0f;
   s->blend_jump = 0.0f;
   s->blend_airdir = 0.0f;
}

VG_STATIC void player__skate_clear_mechanics( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   s->state.jump_charge    = 0.0f;
   s->state.lift_frames    = 0;
   s->state.flip_rate      = 0.0f;
#if 0
   s->state.steery         = 0.0f;
   s->state.steerx         = 0.0f;
   s->state.steery_s       = 0.0f;
   s->state.steerx_s       = 0.0f;
#endif
   s->state.reverse        = 0.0f;
   s->state.slip           = 0.0f;
   v3_copy( player->rb.co, s->state.prev_pos );

#if 0
   m3x3_identity( s->state.velocity_bias );
   m3x3_identity( s->state.velocity_bias_pstep );
#endif

   v3_zero( s->state.throw_v );
   v3_zero( s->state.trick_vel );
   v3_zero( s->state.trick_euler );
}

VG_STATIC void player__skate_reset( player_instance *player,
                                    ent_spawn *rp )
{
   struct player_skate *s = &player->_skate;
   v3_muladds( player->rb.co, player->rb.to_world[1], 1.0f, s->state.cog );
   v3_zero( player->rb.v );
   v3_zero( s->state.cog_v );
   v4_copy( rp->transform.q, player->rb.q );

   s->state.activity = k_skate_activity_air;
   s->state.activity_prev = k_skate_activity_air;

   player__skate_clear_mechanics( player );
   player__skate_reset_animator( player );

   v3_zero( s->state.head_position );
   s->state.head_position[1] = 1.8f;
}

#endif /* PLAYER_SKATE_C */