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[carveJwlIkooP6JGAAIwe30JlM.git] / player_skate.c

#ifndef PLAYER_SKATE_C
#define PLAYER_SKATE_C

#include "player.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" );
}

/* 
 * 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 )
{
   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;
   }

   return len;

   rb_manifold_filter_coplanar( man, len, 0.05f );

   if( len > 1 )
   {
      rb_manifold_filter_backface( man, len );
      rb_manifold_filter_joint_edges( man, len, 0.05f );
      rb_manifold_filter_pairs( man, len, 0.05f );
   }
   int new_len = rb_manifold_apply_filtered( man, len );
   if( len && !new_len )
      len = 1;
   else
      len = new_len;

   return len;
}
/*
 * Gets the closest grindable edge to the player within max_dist 
 */
VG_STATIC struct grind_edge *skate_collect_grind_edge( v3f p0, v3f p1,
                                                       v3f c0, v3f c1, 
                                                       float max_dist )
{
   bh_iter it;
   bh_iter_init( 0, &it );

   boxf region;

   box_init_inf( region );
   box_addpt( region, p0 );
   box_addpt( region, p1 );
   
   float k_r = max_dist;
   v3_add( (v3f){ k_r, k_r, k_r}, region[1], region[1] );
   v3_add( (v3f){-k_r,-k_r,-k_r}, region[0], region[0] );

   float closest = k_r*k_r;
   struct grind_edge *closest_edge = NULL;
   
   int idx;
   while( bh_next( world.grind_bh, &it, region, &idx ) )
   {
      struct grind_edge *edge = &world.grind_edges[ idx ];

      float s,t;
      v3f pa, pb;

      float d2 = 
         closest_segment_segment( p0, p1, edge->p0, edge->p1, &s,&t, pa, pb );

      if( d2 < closest )
      {
         closest = d2;
         closest_edge = edge;
         v3_copy( pa, c0 );
         v3_copy( pb, c1 );
      }
   }

   return closest_edge;
}

VG_STATIC int skate_grind_collide( player_instance *player, rb_ct *contact )
{
   v3f p0, p1, c0, c1;
   v3_muladds( player->rb.co, player->rb.to_world[2],  0.5f, p0 );
   v3_muladds( player->rb.co, player->rb.to_world[2], -0.5f, p1 );
   v3_muladds( p0, player->rb.to_world[1], 0.08f, p0 );
   v3_muladds( p1, player->rb.to_world[1], 0.08f, p1 );

   float const k_r = 0.25f;
   struct grind_edge *closest_edge = skate_collect_grind_edge( p0, p1, 
                                                               c0, c1, k_r );

   if( closest_edge )
   {
      v3f delta;
      v3_sub( c1, c0, delta );

      if( v3_dot( delta, player->rb.to_world[1] ) > 0.0001f )
      {
         contact->p = v3_length( delta );
         contact->type = k_contact_type_edge;
         contact->element_id = 0;
         v3_copy( c1, contact->co );
         contact->rba = NULL;
         contact->rbb = NULL;

         v3f edge_dir, axis_dir;
         v3_sub( closest_edge->p1, closest_edge->p0, edge_dir );
         v3_normalize( edge_dir );
         v3_cross( (v3f){0.0f,1.0f,0.0f}, edge_dir, axis_dir );
         v3_cross( edge_dir, axis_dir, contact->n );

         return 1;
      }
      else
         return 0;
   }

   return 0;
}

VG_STATIC int skate_grind_scansq( player_instance *player, v3f ra )
{
   v3f pos;
   m4x3_mulv( player->rb.to_world, ra, pos );

   v4f plane;
   v3_copy( player->rb.to_world[2], plane );
   v3_normalize( plane );
   plane[3] = v3_dot( plane, pos );

   boxf box;
   float r = 0.3f;
   v3_add( pos, (v3f){ r, r, r }, box[1] );
   v3_sub( pos, (v3f){ r, r, r }, box[0] );

#if 0
   vg_line_boxf( box, VG__BLUE );
#endif

   m4x3f mtx;
   m3x3_copy( player->rb.to_world, mtx );
   v3_copy( pos, mtx[3] );

#if 0
   debug_sphere( mtx, r, VG__CYAN );
#endif
   
   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, (v3f){0.0f,1.0f,0.0f}, 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];

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

            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 ) )
            {
               break;
            }
         }
      }
   }

   if( sample_count < 2 )
      return 0;

   v3f average_position,
       average_direction;

   v3_zero( average_position );
   v3_zero( average_direction );

   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;

         v3f p0;
         v3_muls( support_axis, sj->co[0], p0 );
         p0[1] += sj->co[1];

         v3_add( average_position, p0, average_position );
         
         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 );
         passed_samples ++;
      }
   }

   if( !passed_samples )
      return 0;

   float div = 1.0f/(float)passed_samples;
   v3_muls( average_position, div, average_position );
   v3_muls( average_direction, div, average_direction ); /* !! not normed */
   
   v3_add( pos, average_position, average_position );
   vg_line_pt3( average_position, 0.02f, VG__GREEN );

   v3f p0, p1;
   v3_muladds( average_position, average_direction,  0.35f, p0 );
   v3_muladds( average_position, average_direction, -0.35f, p1 );
   vg_line( p0, p1, VG__PINK );

#if 0
   if( passed_samples )
   {
      v3f displacement, dir;
      v3_sub( pos, average_position, displacement );
      v3_copy( displacement, dir );
      v3_normalize( dir );

      v3f rv, raW;
      q_mulv( player->rb.q, ra, raW );

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

      v3_muladds( rv, player->rb.to_world[2],
                      -v3_dot( rv, player->rb.to_world[2] ), rv );

      v3f Fd, Fs, F;
      v3_muls( displacement, -k_grind_spring, Fs );
      v3_muls( rv, -k_grind_dampener, Fd );

      v3_add( Fd, Fs, F );
      v3_muls( F, k_rb_delta, F );
      
      v3_add( player->rb.v, F, player->rb.v );
      v3f wa;
      v3_cross( raW, F, wa );
      v3_add( player->rb.w, wa, player->rb.w );

      /* Constraint based */
   }
#endif

   return passed_samples;
}

/*
 *
 * Prediction system
 *
 *
 */

/* 
 * Trace a path given a velocity rotation.
 *
 * TODO: this MIGHT be worth doing RK4 on the gravity field.
 */
VG_STATIC void skate_score_biased_path( v3f co, v3f v, m3x3f vr, 
                                        struct land_prediction *prediction )
{
   float pstep  = VG_TIMESTEP_FIXED * 10.0f;
   float k_bias = 0.96f;

   v3f pco, pco1, pv;
   v3_copy( co, pco );
   v3_muls( v,  k_bias, pv );

   m3x3_mulv( vr, pv, pv );
   v3_muladds( pco, pv, pstep, pco );

   struct grind_edge *best_grind = NULL;
   float closest_grind = INFINITY;

   float grind_score    = INFINITY,
         air_score      = INFINITY,
         time_to_impact = 0.0f;

   prediction->log_length = 0;
   v3_copy( pco, prediction->apex );

   for( int i=0; i<vg_list_size(prediction->log); i++ )
   {
      v3_copy( pco, pco1 );

      pv[1] += -k_gravity * pstep;

      m3x3_mulv( vr, pv, pv );
      v3_muladds( pco, pv, pstep, pco );

      if( pco[1] > prediction->apex[1] )
         v3_copy( pco, prediction->apex );
      
      v3f vdir;

      v3_sub( pco, pco1, vdir );

      float l = v3_length( vdir );
      v3_muls( vdir, 1.0f/l, vdir );

      v3f c0, c1;
      struct grind_edge *ge = skate_collect_grind_edge( pco, pco1,
                                                        c0, c1, 0.4f );

      if( ge && (v3_dot((v3f){0.0f,1.0f,0.0f},vdir) < -0.2f ) )
      {
         float d2 = v3_dist2( c0, c1 );
         if( d2 < closest_grind )
         {
            closest_grind = d2;
            best_grind = ge;
            grind_score = closest_grind * 0.05f;
         }
      }

      v3f n1;

      float t1;
      int idx = spherecast_world( pco1, pco, 0.4f, &t1, n1 );
      if( idx != -1 )
      {
         v3_copy( n1, prediction->n );
         air_score = -v3_dot( pv, n1 );
         
         u32 vert_index = world.scene_geo->arrindices[ idx*3 ];
         struct world_material *mat = world_tri_index_material( vert_index );

         /* Bias prediction towords ramps */
         if( mat->info.flags & k_material_flag_skate_surface )
            air_score *= 0.1f;

         v3_lerp( pco1, pco, t1, prediction->log[ prediction->log_length ++ ] ); 
         time_to_impact += t1 * pstep;
         break;
      }

      time_to_impact += pstep;
      v3_copy( pco, prediction->log[ prediction->log_length ++ ] );
   }

   if( grind_score < air_score )
   {
      prediction->score = grind_score; 
      prediction->type = k_prediction_grind;
   }
   else if( air_score < INFINITY )
   {
      prediction->score = air_score;
      prediction->type = k_prediction_land;
   }
   else
   {
      prediction->score = INFINITY;
      prediction->type = k_prediction_none;
   }

   prediction->land_dist = time_to_impact;
}

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

   float pstep = VG_TIMESTEP_FIXED * 10.0f;
   float best_velocity_delta = -9999.9f;

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

   s->prediction_count = 0;
   m3x3_identity( s->state.velocity_bias );

   float best_vmod   = 0.0f,
         min_score   =  INFINITY,
         max_score   = -INFINITY;

   v3_zero( s->state.apex );
   s->land_dist = 0.0f;

   /*
    * Search a broad selection of futures
    */
   for( int m=-3;m<=12; m++ )
   {
      struct land_prediction *p = &s->predictions[ s->prediction_count ++ ];

      float vmod = ((float)m / 15.0f)*0.09f;

      m3x3f bias;
      v4f bias_q;

      q_axis_angle( bias_q, axis, vmod );
      q_m3x3( bias_q, bias );

      skate_score_biased_path( player->rb.co, player->rb.v, bias, p );

      if( p->type != k_prediction_none )
      {
         if( p->score < min_score )
         {
            min_score = p->score;
            best_vmod = vmod;
            s->land_dist = p->land_dist;
            v3_copy( p->apex, s->state.apex );
         }

         if( p->score > max_score )
            max_score = p->score;
      }
   }

   v4f vr_q;
   q_axis_angle( vr_q, axis, best_vmod*0.1f );
   q_m3x3( vr_q, s->state.velocity_bias );

   q_axis_angle( vr_q, axis, best_vmod );
   q_m3x3( vr_q, s->state.velocity_bias_pstep );

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

      float l = p->score;

      if( l < 0.0f )
      {
         vg_error( "negative score! (%f)\n", l );
      }

      l -= min_score;
      l /= (max_score-min_score);
      l  = 1.0f - l;
      l *= 255.0f;

      p->colour = l;
      p->colour <<= 8;
      p->colour |= 0xff000000;
   }


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

   if( (fabsf(steer[1]) > 0.5f) && (s->land_dist >= 1.0f) )
   {
      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 );
   }
}

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

VG_STATIC void skate_apply_grind_model( player_instance *player,
                                        rb_ct *manifold, int len )
{
   struct player_skate *s = &player->_skate;

   /* FIXME: Queue audio events instead */
   if( len == 0 )
   {
      if( s->state.activity == k_skate_activity_grind )
      {
#if 0
         audio_lock();
         audio_player_set_flags( &audio_player_extra, 
                                 AUDIO_FLAG_SPACIAL_3D );
         audio_player_set_position( &audio_player_extra, player.rb.co );
         audio_player_set_vol( &audio_player_extra, 20.0f );
         audio_player_playclip( &audio_player_extra, &audio_board[6] );
         audio_unlock();
#endif

         s->state.activity = k_skate_activity_air;
      }
      return;
   }

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

#if 0
   s->state.steery -= steer[0] * k_steer_air * k_rb_delta;
   s->state.steerx += steer[1] * s->state.reverse * k_steer_air * k_rb_delta;
#endif
   
#if 0
   v4f rotate;
   q_axis_angle( rotate, player->rb.to_world[0], siX );
   q_mul( rotate, player.rb.q, player.rb.q );
#endif

   s->state.slip = 0.0f;
   s->state.activity = k_skate_activity_grind;

   /* TODO: Compression */
   v3f up = { 0.0f, 1.0f, 0.0f };
   float angle = v3_dot( player->rb.to_world[1], up );

   if( fabsf(angle) < 0.99f )
   {
      v3f axis; 
      v3_cross( player->rb.to_world[1], up, axis );

      v4f correction;
      q_axis_angle( correction, axis, k_rb_delta * 10.0f * acosf(angle) );
      q_mul( correction, player->rb.q, player->rb.q );
   }

   float const DOWNFORCE = -k_downforce*1.2f*VG_TIMESTEP_FIXED;
   v3_muladds( player->rb.v, manifold->n, DOWNFORCE, player->rb.v );
   m3x3_identity( s->state.velocity_bias );
   m3x3_identity( s->state.velocity_bias_pstep );

   if( s->state.activity_prev != k_skate_activity_grind )
   {
      /* FIXME: Queue audio events instead */
#if 0
      audio_lock();
      audio_player_set_flags( &audio_player_extra, 
                              AUDIO_FLAG_SPACIAL_3D );
      audio_player_set_position( &audio_player_extra, player.rb.co );
      audio_player_set_vol( &audio_player_extra, 20.0f );
      audio_player_playclip( &audio_player_extra, &audio_board[5] );
      audio_unlock();
#endif
   }
}

/*
 * 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 != k_skate_activity_air )
      return;

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

   m3x3_mulv( s->state.velocity_bias, player->rb.v, player->rb.v );
   ray_hit hit;

   /* 
    * Prediction 
    */
   float pstep  = VG_TIMESTEP_FIXED * 1.0f;
   float k_bias = 0.98f;

   v3f pco, pco1, pv;
   v3_copy( player->rb.co, pco );
   v3_muls( player->rb.v, 1.0f, pv );
   
   float time_to_impact = 0.0f;
   float limiter = 1.0f;

   struct grind_edge *best_grind = NULL;
   float closest_grind = INFINITY;

   v3f target_normal = { 0.0f, 1.0f, 0.0f };
   int has_target = 0;

   for( int i=0; i<250; i++ )
   {
      v3_copy( pco, pco1 );
      m3x3_mulv( s->state.velocity_bias, pv, pv );

      pv[1] += -k_gravity * pstep;
      v3_muladds( pco, pv, pstep, pco );
      
      ray_hit contact;
      v3f vdir;

      v3_sub( pco, pco1, vdir );
      contact.dist = v3_length( vdir );
      v3_divs( vdir, contact.dist, vdir);

      v3f c0, c1;
      struct grind_edge *ge = skate_collect_grind_edge( pco, pco1,
                                                        c0, c1, 0.4f );

      if( ge && (v3_dot((v3f){0.0f,1.0f,0.0f},vdir) < -0.2f ) ) 
      { 
         vg_line( ge->p0, ge->p1, 0xff0000ff ); 
         vg_line_cross( pco, 0xff0000ff, 0.25f );
         has_target = 1;
         break;
      }
      
      float orig_dist = contact.dist;
      if( ray_world( pco1, vdir, &contact ) )
      {
         v3_copy( contact.normal, target_normal );
         has_target = 1;
         time_to_impact += (contact.dist/orig_dist)*pstep;
         vg_line_cross( contact.pos, 0xffff0000, 0.25f );
         break;
      }
      time_to_impact += pstep;
   }

   if( has_target )
   {
      float angle = v3_dot( player->rb.to_world[1], target_normal );
      v3f axis; 
      v3_cross( player->rb.to_world[1], target_normal, axis );

      limiter = vg_minf( 5.0f, time_to_impact )/5.0f;
      limiter = 1.0f-limiter;
      limiter *= limiter;
      limiter = 1.0f-limiter;

      if( fabsf(angle) < 0.9999f )
      {
         v4f correction;
         q_axis_angle( correction, axis, 
                        acosf(angle)*(1.0f-limiter)*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 );

#if 0
   s->state.steery -= steer[0] * k_steer_air * VG_TIMESTEP_FIXED;
   s->state.steerx += steer[1] * s->state.reverse * k_steer_air 
                                                         * limiter * k_rb_delta;
#endif
   s->land_dist = time_to_impact;
   v3_copy( target_normal, s->land_normal );
}

VG_STATIC void skate_get_board_points( player_instance *player,
                                       v3f front, v3f back )
{
   v3f pos_front = {0.0f,0.0f,-k_board_length},
       pos_back  = {0.0f,0.0f, k_board_length};

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

/*
 * Casts and pushes a sphere-spring model into the world
 */
VG_STATIC int skate_simulate_spring( player_instance *player,
                                     v3f pos )
{
   struct player_skate *s = &player->_skate;

   float mod      = 0.7f * player->input_grab->axis.value + 0.3f,
         spring_k = mod * k_spring_force,
         damp_k   = mod * k_spring_dampener,
         disp_k   = 0.4f;

   v3f start, end;
   v3_copy( pos, start );
   v3_muladds( pos, player->rb.to_world[1], -disp_k, end );

   float t;
   v3f n;
   int hit_info = spherecast_world( start, end, 0.2f, &t, n );

   if( hit_info != -1 )
   {
      v3f F, delta;
      v3_sub( start, player->rb.co, delta );
      
      float displacement = vg_clampf( 1.0f-t, 0.0f, 1.0f ),
            damp         = 
         vg_maxf( 0.0f, v3_dot( player->rb.to_world[1], player->rb.v ) );

      v3_muls( player->rb.to_world[1], displacement*spring_k*k_rb_delta -
                                       damp*damp_k*k_rb_delta, F );

      v3_muladds( player->rb.v, F, 1.0f, player->rb.v );
      
      /* Angular velocity */
      v3f wa;
      v3_cross( delta, F, wa );
      v3_muladds( player->rb.w, wa, k_spring_angular, player->rb.w );

      v3_lerp( start, end, t, pos );
      return 1;
   }
   else
   {
      v3_copy( end, pos );
      return 0;
   }
}


/* 
 * Handles connection between the player and the ground
 *
 * TODO: Must save original velocity to use here
 */
VG_STATIC void skate_apply_interface_model( player_instance *player,
                                            rb_ct *manifold, int len )
{
   struct player_skate *s = &player->_skate;

   if( !((s->state.activity == k_skate_activity_ground) ||
         (s->state.activity == k_skate_activity_air )) )
      return;

   if( s->state.activity == k_skate_activity_air )
      s->debug_normal_pressure = 0.0f;
   else
      s->debug_normal_pressure = v3_dot( player->rb.to_world[1], player->rb.v );

   /* springs */
   v3f spring0, spring1;

   skate_get_board_points( player, spring1, spring0 );
   int spring_hit0 = 0, //skate_simulate_spring( player, s, spring0 ),
       spring_hit1 = 0; //skate_simulate_spring( player, s, spring1 );

   v3f animavg, animdelta;
   v3_add( spring0, spring1, animavg );
   v3_muls( animavg, 0.5f, animavg );

   v3_sub( spring1, spring0, animdelta );
   v3_normalize( animdelta );

   m4x3_mulv( player->rb.to_local, animavg, s->board_offset );

   float dx = -v3_dot( animdelta, player->rb.to_world[2] ),
         dy =  v3_dot( animdelta, player->rb.to_world[1] );

   float angle = -atan2f( dy, dx );
   q_axis_angle( s->board_rotation, (v3f){1.0f,0.0f,0.0f}, angle );

   int lift_frames_limit = 6;

   /* Surface connection */
   if( len == 0 && !(spring_hit0 && spring_hit1) )
   {
      s->state.lift_frames ++;

      if( s->state.lift_frames >= lift_frames_limit )
         s->state.activity = k_skate_activity_air;
   }
   else
   {
      v3f surface_avg;
      v3_zero( surface_avg );

      for( int i=0; i<len; i++ )
         v3_add( surface_avg, manifold[i].n, surface_avg );
      v3_normalize( surface_avg );
      
      if( v3_dot( player->rb.v, surface_avg ) > 0.7f )
      {
         s->state.lift_frames ++;

         if( s->state.lift_frames >= lift_frames_limit )
            s->state.activity = k_skate_activity_air;
      }
      else
      {
         s->state.activity = k_skate_activity_ground;
         s->state.lift_frames = 0;
         v3f projected, axis;

         if( s->state.activity_prev == k_skate_activity_air )
         {
            player->cam_land_punch_v += v3_dot( player->rb.v, surface_avg ) *
                                          k_cam_punch;
         }

         float const DOWNFORCE = -k_downforce*VG_TIMESTEP_FIXED;
         v3_muladds( player->rb.v, player->rb.to_world[1], 
                     DOWNFORCE, player->rb.v );

         float d = v3_dot( player->rb.to_world[2], surface_avg );
         v3_muladds( surface_avg, player->rb.to_world[2], -d, projected );
         v3_normalize( projected );

         float angle = v3_dot( player->rb.to_world[1], projected );
         v3_cross( player->rb.to_world[1], projected, axis );

#if 0
         if( fabsf(angle) < 0.9999f )
         {
            v4f correction;
            q_axis_angle( correction, axis, 
                          acosf(angle)*4.0f*VG_TIMESTEP_FIXED );
            q_mul( correction, player->rb.q, player->rb.q );
         }
#endif
      }
   }
}

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( (s->state.lift_frames == 0) 
          && (v3_length2(s->state.trick_vel) >= 0.0001f ) &&
          s->state.trick_time > 0.2f)
      {
         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 );
}

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

   if( s->state.activity != k_skate_activity_ground )
      return;

   /*
    * 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 )
      {
         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 );
   
   /* Steering */
   float input = player->input_js1h->axis.value,
         grab  = player->input_grab->axis.value,
         steer = input * (1.0f-(s->state.jump_charge+grab)*0.4f),
         steer_scaled = vg_signf(steer) * powf(steer,2.0f) * k_steer_ground;

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

   float current  = v3_dot( player->rb.to_world[1], player->rb.w ),
         addspeed = (steer_scaled * -1.0f) - current,
         maxaccel = 26.0f * k_rb_delta,
         accel    = vg_clampf( addspeed, -maxaccel, maxaccel );

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


#if 0
   player_accelerate( player->rb.w, steer_axis,
                      fabsf(steer_scaled) * 1.0f, 30.0f );

   //s->state.steery -= steer_scaled * k_rb_delta;
#endif
}

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_ground )
      s->state.charging_jump = 0;

   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 * VG_TIMESTEP_FIXED;
   }

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

   if( s->state.activity == k_skate_activity_air )
      return;

   /* 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( (v3f){0.0f,1.0f,0.0f}, 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;

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

#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;
#endif
      s->state.lift_frames ++;

      /* FIXME audio events */
#if 0
      audio_lock();
      audio_player_set_flags( &audio_player_extra, AUDIO_FLAG_SPACIAL_3D );
      audio_player_set_position( &audio_player_extra, player.rb.co );
      audio_player_set_vol( &audio_player_extra, 20.0f );
      audio_player_playclip( &audio_player_extra, &audio_jumps[rand()%2] );
      audio_unlock();
#endif
   }
}

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

   /* 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;
   v3_muladds( player->rb.co, player->rb.to_world[1],
               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 );
   s->state.cog_v[1] += -9.8f * k_rb_delta;
   v3_muladds( s->state.cog, s->state.cog_v, k_rb_delta, s->state.cog );
}

VG_STATIC void skate_collision_response( player_instance *player,
                                         rb_ct *manifold, int len )
{
   struct player_skate *s = &player->_skate;

   for( int j=0; j<10; j++ )
   {
      for( int i=0; i<len; i++ )
      {
         struct contact *ct = &manifold[i];
         
         v3f rv, delta;
         v3_sub( ct->co, player->rb.co, delta ); 
         v3_cross( player->rb.w, delta, rv );
         v3_add( player->rb.v, rv, rv );

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

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

         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 );

         if( fabsf(v3_dot( impulse, player->rb.to_world[2] )) > 10.0f ||
             fabsf(v3_dot( impulse, player->rb.to_world[1] )) > 50.0f )
         {
            player__dead_transition( player );
            return;
         }

         v3_add( impulse, player->rb.v, player->rb.v );
         v3_cross( delta, impulse, impulse );

         /*
          * W Impulses are limited to the Y and X axises, we don't really want
          * roll angular velocities being included.
          *
          * Can also tweak the resistance of each axis here by scaling the wx,wy
          * components.
          */
         
         float wy = v3_dot( player->rb.to_world[1], impulse ) * 1.0f,
               wx = v3_dot( player->rb.to_world[0], impulse ) * 1.0f,
               wz = v3_dot( player->rb.to_world[2], impulse ) * 1.0f;

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


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

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

   /* integrate rigidbody velocities */
#ifndef SKATE_CCD
   v3f gravity = { 0.0f, -9.6f, 0.0f };
   v3_muladds( player->rb.v, gravity, k_rb_delta, player->rb.v );
   v3_muladds( player->rb.co, player->rb.v, k_rb_delta, player->rb.co );
#endif

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

#if 0
   if( s->state.activity == k_skate_activity_air )
   {
      float dist = 1.0f-(s->land_dist/4.0f);
      decay_rate = 0.5f * vg_maxf( dist*dist, 0.0f );
   }
#endif

   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] ),
         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 );

#ifndef SKATE_CCD
   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*k_rb_delta );
      q_mul( rotation, player->rb.q, player->rb.q );
   }
#endif

   /* integrate steering velocities */
#if 0
   v4f rotate; 
   float l = (s->state.activity == k_skate_activity_air)? 0.04f: 0.24f;

   s->state.steery_s = vg_lerpf( s->state.steery_s, s->state.steery, l );
   s->state.steerx_s = vg_lerpf( s->state.steerx_s, s->state.steerx, l );

   q_axis_angle( rotate, player->rb.to_world[1], s->state.steery_s );
   q_mul( rotate, player->rb.q, player->rb.q );

   q_axis_angle( rotate, player->rb.to_world[0], s->state.steerx_s );
   q_mul( rotate, player->rb.q, player->rb.q );

   s->state.steerx = 0.0f;
   s->state.steery = 0.0f;
#endif

   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__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.lift_frames > 0) &&
       (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 ++ )
         vg_line( p->log[j], p->log[j+1], 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 );
   }

   vg_line_pt3( s->state.apex, 0.200f, 0xff0000ff );
   vg_line_pt3( s->state.apex, 0.201f, 0xff00ffff );
}

VG_STATIC void player__skate_update( player_instance *player )
{
   struct player_skate *s = &player->_skate;
   v3_copy( player->rb.co, s->state.prev_pos );
   s->state.activity_prev = s->state.activity;

   struct board_collider
   {
      v3f   pos;
      float radius;

      int   apply_angular;
      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 = 0.07f, 
         .apply_angular = 1,
         .colour = VG__RED
      },
      { 
         { 0.0f, 0.0f,     k_board_length }, 
         .radius = 0.07f,
         .apply_angular = 1,
         .colour = VG__GREEN
      },
      { 
         { 0.0f, k_board_end_radius,    -k_board_length - k_board_end_radius }, 
         .radius = k_board_end_radius,
         .apply_angular = 0,
         .colour = VG__YELOW
      },
      {  
         { 0.0f, k_board_end_radius,     k_board_length + k_board_end_radius },
         .radius = k_board_end_radius,
         .apply_angular = 0,
         .colour = VG__YELOW
      },
   };

   const int k_wheel_count = 4;

   if( skate_grind_scansq( player, (v3f){ 0.0f, 0.0f, -k_board_length } ) )
   {
#if 0
      wheel_states[0] = 0;
      wheel_states[1] = 0;
#endif
   }

   if( skate_grind_scansq( player, (v3f){ 0.0f, 0.0f,  k_board_length } ) )
   {
#if 0
      wheel_states[2] = 0;
      wheel_states[3] = 0;
#endif
   }

   s->substep = k_rb_delta;
   int substep_count = 0;

   v3f original_velocity;
   v3_muladds( player->rb.v, (v3f){0.0f,-k_gravity,0.0f}, 
               k_rb_delta, original_velocity );

begin_collision:;

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

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

   /* 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 );
   }

   /* 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;
      q_mulv( future_q, wheels[i].pos, future );
      v3_add( future, future_co, 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 * 1.2f;
      if( spherecast_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 );
   }

   rb_update_transform( &player->rb );

   v3f gravity = { 0.0f, -9.6f, 0.0f };
   v3_muladds( player->rb.v, gravity, s->substep_delta, player->rb.v );

   s->substep -= s->substep_delta;

   /*
    * Phase 1: Regular collision detection
    *          TODO: Me might want to automatically add contacts from CCD, 
    *                since at high angular velocities, theres a small change
    *                that discreet detection will miss.
    * --------------------------------------------------------------------------
    */

   rb_ct manifold[128];
         
   int manifold_len   = 0;

   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;

      /* for non-angular contacts we just want Y. contact positions are
       * snapped to the local xz plane */
      if( !wheels[i].apply_angular )
      {
         for( int j=0; j<l; j++ )
         {
            v3f ra;
            v3_sub( man[j].co, player->rb.co, ra );

            float dy = v3_dot( player->rb.to_world[1], ra );
            v3_muladds( man[j].co, player->rb.to_world[1], -dy, man[j].co );
         }
      }

      manifold_len += l;
   }

   /* 
    * Phase 2: Truck alignment (spring/dampener model)
    *          it uses the first two colliders as truck positions
    * --------------------------------------------------------------------------
    */

   v3f surface_picture;
   v3_zero( surface_picture );
   
   for( int i=0; i<2; i++ )
   {
      v3f truck, left, right;
      m4x3_mulv( player->rb.to_world, wheels[i].pos, 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, wheels[i].colour );

      v3_muladds( left,  player->rb.to_world[1], 0.1f, left  );
      v3_muladds( right, player->rb.to_world[1], 0.1f, right );

      float k_max_truck_flex = VG_PIf * 0.25f;
      
      ray_hit ray_l, ray_r;
      ray_l.dist = 0.2f;
      ray_r.dist = 0.2f;

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

      int res_l = ray_world( left, dir, &ray_l ),
          res_r = ray_world( right, dir, &ray_r );

      /* ignore bad normals */
      if( res_l )
      {
         if( v3_dot( ray_l.normal, player->rb.to_world[1] ) < 0.7071f )
            res_l = 0;
         else
            v3_add( ray_l.normal, surface_picture, surface_picture );
      }

      if( res_r )
      {
         if( v3_dot( ray_r.normal, player->rb.to_world[1] ) < 0.7071f )
            res_r = 0;
         else
            v3_add( ray_l.normal, surface_picture, surface_picture );
      }

      v3f v0;
      v3f midpoint;
      v3_muladds( truck, player->rb.to_world[1], -wheels[i].radius, midpoint );

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

         if( res_l ) v3_copy( ray_l.pos, p0 );
         if( res_r ) v3_copy( ray_r.pos, p1 );

         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 v0, v1, n;
            v3_sub( verts[1], verts[0], v0 );
            v3_sub( verts[2], verts[0], v1 );
            v3_cross( v0, v1, n );
            v3_normalize( n );

            if( v3_dot( n, player->rb.to_world[1] ) < 0.7071f )
               continue;

            continue;
         }
         else
            continue;
      }

      float a = vg_clampf( v3_dot( v0, player->rb.to_world[0] ), -1.0f, 1.0f );
      a = acosf( a );

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

      vg_line( left, right, VG__WHITE );

      v3f axis;
      v3_cross( v0, player->rb.to_world[0], axis );

      float Fs = -a * k_board_spring,
            Fd = -v3_dot( player->rb.w, axis ) * k_board_dampener;

      v3_muladds( player->rb.w, axis, (Fs+Fd) * s->substep_delta,
                  player->rb.w );
   }

   /* 
    * Phase 2a: Manual alignment (spring/dampener model)
    * --------------------------------------------------------------------------
    */

   v3f weight, world_cog;
   v3_zero( weight );

   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.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 )
         {
            player__dead_transition( player );
            return;
         }
      }
   }

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

   m4x3_mulv( player->rb.to_world, weight, world_cog );
   vg_line_pt3( world_cog, 0.1f, VG__BLACK );

   /* TODO: Fall back on land normal */
   /* TODO: Lerp weight distribution */

   if( v3_length2( surface_picture ) > 0.001f && 
       v3_length2( weight ) > 0.001f &&
       s->state.manual_direction )
   {
      v3_normalize( surface_picture );
      v3f plane_z;

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

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

      v3_muladds( plane_z, 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 );

      float a = v3_dot( plane_z, refdir );
      a = acosf( vg_clampf( a, -1.0f, 1.0f ) );

      v3f axis;
      v3_cross( plane_z, refdir, axis );

      float Fs = -a * k_manul_spring,
            Fd = -v3_dot( player->rb.w, axis ) * k_manul_dampener;

      v3_muladds( player->rb.w, axis, (Fs+Fd) * s->substep_delta,
                  player->rb.w );
   }

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

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

   /* 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 + ct->bias );

         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 );
      }
   }

   substep_count ++;

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

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

   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 ]);
   }

   v3f velocity_change, p1;
   v3_sub( player->rb.v, original_velocity, velocity_change );

   v3_normalize( velocity_change );
   v3_muladds( player->rb.co, velocity_change, 2.0f, p1 );
   vg_line( player->rb.co, p1, VG__PINK );

#if 0
   skate_apply_grind_model( player, &manifold[manifold_len], grind_len );
#endif

   skate_apply_interface_model( player, manifold, manifold_len );
   
   skate_apply_pump_model( player );
   skate_apply_cog_model( player );

   skate_apply_grab_model( player );
   skate_apply_friction_model( player );
   skate_apply_jump_model( player );
   skate_apply_air_model( player );
   skate_apply_trick_model( player );

   skate_integrate( player );

   vg_line_pt3( s->state.cog, 0.1f,  VG__WHITE );
   vg_line_pt3( s->state.cog, 0.11f, VG__WHITE );
   vg_line_pt3( s->state.cog, 0.12f, VG__WHITE );
   vg_line_pt3( s->state.cog, 0.13f, VG__WHITE );
   vg_line_pt3( s->state.cog, 0.14f, VG__WHITE );

   vg_line( player->rb.co, s->state.cog, VG__RED );

   teleport_gate *gate;
   if( (gate = world_intersect_gates( player->rb.co, s->state.prev_pos )) )
   {
      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 );

      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 );
   }
}

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

   /* FIXME: Compression */
   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] );

   player__debugtext( 1, "activity: %s",
                           (const char *[]){ "k_skate_activity_air",
                                             "k_skate_activity_ground",
                                             "k_skate_activity_grind }" }
                                             [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 );

   m4x3_mulv( player->rb.to_local, s->state.cog, offset );
   v3_muls( offset, -4.0f, offset );

   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) ||
                 (s->state.activity == k_skate_activity_grind );

      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;

      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 );
   }

   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;
      }

      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];

      v3f bo;
      v3_muls( s->board_offset, add_grab_mod, bo );

      v3_add( bo, kf_board->co,  kf_board->co );
      v3_add( bo, kf_foot_l->co, kf_foot_l->co );
      v3_add( bo, kf_foot_r->co, kf_foot_r->co );

#if 0
      m3x3f c;
      q_m3x3( s->board_rotation, c );
#endif

      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, qtrickr );
      q_mul( s->board_rotation, qtrickr, qtotal );
      q_normalize( qtotal );

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


      v3f d;
      v3_sub( kf_foot_l->co, bo, d );
      q_mulv( qtotal, d, d );
      v3_add( bo, d, kf_foot_l->co );
      
      v3_sub( kf_foot_r->co, bo, d );
      q_mulv( qtotal, d, d );
      v3_add( bo, d, kf_foot_r->co );

      q_mul( s->board_rotation, kf_board->q, kf_board->q );
      q_normalize( 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 );
   }

   /* 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 );
#if 0
   v4f qresy, qresx, qresidual;
   m3x3f mtx_residual;
   q_axis_angle( qresy, player->rb.to_world[1], s->state.steery_s*substep );
   q_axis_angle( qresx, player->rb.to_world[0], s->state.steerx_s*substep );

   q_mul( qresy, qresx, qresidual );
   q_normalize( qresidual );
   q_mul( dest->root_q, qresidual, dest->root_q );
   q_normalize( dest->root_q );
#endif

   v4f qflip;
   if( (s->state.activity == k_skate_activity_air) &&
       (fabsf(s->state.flip_rate) > 0.01f) )
   {
      float t = s->state.flip_time + s->state.flip_rate*substep*k_rb_delta,
            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 );
   }
}

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;
}

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 );

   m3x3_identity( s->state.velocity_bias );
   m3x3_identity( s->state.velocity_bias_pstep );
   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,
                                    struct respawn_point *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->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 );
}

#endif /* PLAYER_SKATE_C */