a fairly major physics update

[carveJwlIkooP6JGAAIwe30JlM.git] / player_physics.h

/*
 * Copyright (C) 2021-2022 Mt.ZERO Software, Harry Godden - All Rights Reserved
 */

#ifndef PLAYER_PHYSICS_H
#define PLAYER_PHYSICS_H

#include "player.h"
#include "camera.h"

VG_STATIC void apply_gravity( v3f vel, float const timestep )
{
   v3f gravity = { 0.0f, -9.6f, 0.0f };
   v3_muladds( vel, gravity, timestep, vel );
}

VG_STATIC struct 
grind_edge *player_grind_collect_edge( v3f p0, v3f p1,
                                       v3f c0, v3f c1, float max_dist )
{
   struct player_phys *phys = &player.phys;

   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;
}

/*
 * Cast a sphere from a to b and see what time it hits
 */
VG_STATIC int spherecast_world( v3f pa, v3f pb, float r, float *t, v3f n )
{
   struct player_phys *phys = &player.phys;

   bh_iter it;
   bh_iter_init( 0, &it );

   boxf region;
   box_init_inf( region );
   box_addpt( region, pa );
   box_addpt( region, pb );
   
   v3_add( (v3f){ r, r, r}, region[1], region[1] );
   v3_add( (v3f){-r,-r,-r}, region[0], region[0] );

   v3f dir;
   v3_sub( pb, pa, dir );

   int hit = -1;
   float min_t = 1.0f;

   int idx;
   while( bh_next( world.geo_bh, &it, region, &idx ) )
   {
      u32 *ptri = &world.scene_geo->arrindices[ idx*3 ];
      v3f tri[3];

      boxf box;
      box_init_inf( box );

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

      v3_add( (v3f){ r, r, r}, box[1], box[1] );
      v3_add( (v3f){-r,-r,-r}, box[0], box[0] );
      if( !ray_aabb( box, pa, dir, 1.0f ) )
         continue;
      
      float t;
      v3f n1;
      if( spherecast_triangle( tri, pa, dir, r, &t, n1 ) )
      {
         if( t < min_t )
         {
            min_t = t;
            hit = idx;
            v3_copy( n1, n );
         }
      }
   }

   *t = min_t;
   return hit;
}

/* 
 * Trace a path given a velocity rotation.
 * Closest to 0 is best.
 */
VG_STATIC void player_predict_land( m3x3f vr, 
                                    struct land_prediction *prediction )
{
   struct player_phys *phys = &player.phys;

   float pstep  = VG_TIMESTEP_FIXED * 10.0f;
   float k_bias = 0.96f;

   v3f pco, pco1, pv;
   v3_copy( phys->rb.co, pco );
   v3_muls( phys->rb.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;

   prediction->log_length = 0;

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

      m3x3_mulv( vr, pv, pv );
      v3_muladds( pco, pv, pstep, pco );
      
      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 = player_grind_collect_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 ++ ] ); 
         break;
      }

      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;
   }
}

/*
 * Called when launching into the air to predict and adjust trajectories
 */
VG_STATIC void player_start_air(void)
{
   struct player_phys *phys = &player.phys;

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

   v3f axis;
   v3_cross( phys->rb.up, phys->rb.v, axis );
   v3_normalize( axis );
   player.prediction_count = 0;
   
   m3x3_identity( phys->vr );

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

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

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

      m3x3f vr;
      v4f vr_q;

      q_axis_angle( vr_q, axis, vmod );
      q_m3x3( vr_q, vr );

      player_predict_land( vr, p );

      if( p->type != k_prediction_none )
      {
         if( p->score < min_score )
         {
            min_score = p->score;
            best_vmod = vmod;
         }

         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, phys->vr );

   q_axis_angle( vr_q, axis, best_vmod );
   q_m3x3( vr_q, phys->vr_pstep );

   /*
    * Logging
    */
   for( int i=0; i<player.prediction_count; i ++ )
   {
      struct land_prediction *p = &player.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;
   }
}


VG_STATIC void player_physics_control_passive(void)
{
   struct player_phys *phys = &player.phys;
   float grabt = player.input_grab->axis.value;

   if( grabt > 0.5f )
   {
      v2_muladds( phys->grab_mouse_delta, vg.mouse_delta, 0.02f, 
                  phys->grab_mouse_delta );
      v2_normalize_clamp( phys->grab_mouse_delta );

      if( freecam )
         v2_zero( phys->grab_mouse_delta );
   }
   else
      v2_zero( phys->grab_mouse_delta );

   phys->grab = vg_lerpf( phys->grab, grabt, 0.14f );
   player.phys.pushing = 0.0f;

   if( !phys->jump_charge || phys->in_air )
   {
      phys->jump -= k_jump_charge_speed * VG_TIMESTEP_FIXED;
   }

   phys->jump_charge = 0;
   phys->jump = vg_clampf( phys->jump, 0.0f, 1.0f );
}

/*
 * Main friction interface model
 */
VG_STATIC void player_physics_control(void)
{
   struct player_phys *phys = &player.phys;

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

   v3f vel;
   m3x3_mulv( phys->rb.to_local, phys->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;
   phys->slip = slip;
   phys->reverse = -vg_signf(vel[2]);

   float substep = VG_TIMESTEP_FIXED * 0.2f;
   float fwd_resistance = k_friction_resistance;

   for( int i=0; i<5; i++ )
   {
      vel[2] = stable_force( vel[2],vg_signf(vel[2]) * -fwd_resistance*substep);
      vel[0] = stable_force( vel[0],vg_signf(vel[0]) * -k_friction_lat*substep);
   }
   
   if( player.input_jump->button.value )
   {
      phys->jump += VG_TIMESTEP_FIXED * k_jump_charge_speed;

      if( !phys->jump_charge )
         phys->jump_dir = phys->reverse > 0.0f? 1: 0;

      phys->jump_charge = 1;
   }

   static int push_thresh_last = 0;
   float push = player.input_push->button.value;
   int push_thresh = push>0.15f? 1: 0;
   
   if( push_thresh && !push_thresh_last )
      player.phys.start_push = vg.time;

   push_thresh_last = push_thresh;

   if( !player.input_jump->button.value && push_thresh )
   {
      player.phys.pushing = 1.0f;
      player.phys.push_time = vg.time - player.phys.start_push;

      float cycle_time = player.phys.push_time*k_push_cycle_rate,
            amt = k_push_accel * (sinf(cycle_time)*0.5f+0.5f)*VG_TIMESTEP_FIXED,
            current = v3_length( vel ),
            new_vel = vg_minf( current + amt, k_max_push_speed );

      new_vel -= vg_minf(current, k_max_push_speed);
      vel[2] -= new_vel * phys->reverse;
   }

   m3x3_mulv( phys->rb.to_world, vel, phys->rb.v );
   
   float input = player.input_js1h->axis.value,
         grab  = player.input_grab->axis.value,
         steer = input * (1.0f-(phys->jump+grab)*0.4f),
         steer_scaled = vg_signf(steer) * powf(steer,2.0f) * k_steer_ground;

   phys->iY -= steer_scaled * VG_TIMESTEP_FIXED;

   if( !phys->jump_charge && phys->jump > 0.2f )
   {
      v3f jumpdir;
      
      /* Launch more up if alignment is up else improve velocity */
      float aup = fabsf(v3_dot( (v3f){0.0f,1.0f,0.0f}, phys->rb.up )),
            mod = 0.5f,
            dir = mod + aup*(1.0f-mod);

      v3_copy( phys->rb.v, jumpdir );
      v3_normalize( jumpdir );
      v3_muls( jumpdir, 1.0f-dir, jumpdir );
      v3_muladds( jumpdir, phys->rb.up, dir, jumpdir );
      v3_normalize( jumpdir );
      
      float force = k_jump_force*phys->jump;
      v3_muladds( phys->rb.v, jumpdir, force, phys->rb.v );
      phys->jump = 0.0f;

      player.jump_time = vg.time;
      
      /* TODO: Move to audio file */
      audio_lock();
      audio_player_set_flags( &audio_player_extra, AUDIO_FLAG_SPACIAL_3D );
      audio_player_set_position( &audio_player_extra, phys->rb.co );
      audio_player_set_vol( &audio_player_extra, 20.0f );
      audio_player_playclip( &audio_player_extra, &audio_jumps[rand()%2] );
      audio_unlock();
   }
}

VG_STATIC void player_physics_control_grind(void)
{
   struct player_phys *phys = &player.phys;
   v2f steer = { player.input_js1h->axis.value,
                 player.input_js1v->axis.value };

   float l2 = v2_length2( steer );
   if( l2 > 1.0f )
      v2_muls( steer, 1.0f/sqrtf(l2), steer );

   phys->iY -= steer[0] * k_steer_air * VG_TIMESTEP_FIXED;

   float iX = steer[1] * phys->reverse * k_steer_air * VG_TIMESTEP_FIXED;

   static float siX = 0.0f;
   siX = vg_lerpf( siX, iX, k_steer_air_lerp );
   
   v4f rotate;
   q_axis_angle( rotate, phys->rb.right, siX );
   q_mul( rotate, phys->rb.q, phys->rb.q );

   phys->slip = 0.0f;
}

/*
 * Air control, no real physics
 */
VG_STATIC void player_physics_control_air(void)
{
   struct player_phys *phys = &player.phys;

   m3x3_mulv( phys->vr, phys->rb.v, phys->rb.v );
   //vg_line_cross( player.land_target, 0xff0000ff, 0.25f );

   ray_hit hit;

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

   v3f pco, pco1, pv;
   v3_copy( phys->rb.co, pco );
   v3_muls( phys->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( phys->vr, pv, pv );
      apply_gravity( pv, 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 = player_grind_collect_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( phys->rb.up, target_normal );
      v3f axis; 
      v3_cross( phys->rb.up, 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) < 0.99f )
      {
         v4f correction;
         q_axis_angle( correction, axis, 
                        acosf(angle)*(1.0f-limiter)*3.0f*VG_TIMESTEP_FIXED );
         q_mul( correction, phys->rb.q, phys->rb.q );
      }
   }

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

   float l2 = v2_length2( steer );
   if( l2 > 1.0f )
      v2_muls( steer, 1.0f/sqrtf(l2), steer );

   phys->iY -= steer[0] * k_steer_air * VG_TIMESTEP_FIXED;

   float iX = steer[1] * 
              phys->reverse * k_steer_air * limiter * VG_TIMESTEP_FIXED;

   static float siX = 0.0f;
   siX = vg_lerpf( siX, iX, k_steer_air_lerp );
   
   v4f rotate;
   q_axis_angle( rotate, phys->rb.right, siX );
   q_mul( rotate, phys->rb.q, phys->rb.q );
   
#if 0
   v2f target = {0.0f,0.0f};
   v2_muladds( target, (v2f){ vg_get_axis("grabh"), vg_get_axis("grabv") },
               phys->grab, target );
#endif
}

VG_STATIC void player_walk_update_collision(void)
{
   struct player_phys *phys = &player.phys;
   float h0 = 0.3f,
         h1 = 0.9f;

   rigidbody *rbf = &player.collide_front,
             *rbb = &player.collide_back;

   v3_add( phys->rb.co, (v3f){0.0f,h0,0.0f}, rbf->co );
   v3_add( phys->rb.co, (v3f){0.0f,h1,0.0f}, rbb->co );
   v3_copy( rbf->co, rbf->to_world[3] );
   v3_copy( rbb->co, rbb->to_world[3] );
   m4x3_invert_affine( rbf->to_world, rbf->to_local );
   m4x3_invert_affine( rbb->to_world, rbb->to_local );

   rb_update_bounds( rbf );
   rb_update_bounds( rbb );
}

VG_STATIC void player_integrate(void);

VG_STATIC int player_walk_surface_standable( v3f n )
{
   return v3_dot( n, (v3f){0.0f,1.0f,0.0f} ) > 0.5f;
}

VG_STATIC void player_walk_stepdown(void)
{
   struct player_phys *phys = &player.phys;
   float max_dist = 0.4f;

   v3f pa, pb;
   v3_copy( phys->rb.co, pa );
   pa[1] += 0.3f;

   v3_muladds( pa, (v3f){0.01f,1.0f,0.01f}, -max_dist, pb );
   vg_line( pa, pb, 0xff000000 );

   /* TODO: Make #define */
   float r = 0.3f,
         t;

   v3f n;
   if( spherecast_world( pa, pb, r, &t, n ) != -1 )
   {
      if( player_walk_surface_standable( n ) )
      {
         phys->in_air = 0;
         v3_lerp( pa, pb, t+0.001f, phys->rb.co );
         phys->rb.co[1] -= 0.3f;
      }
   }
}

/*
 * Entire Walking physics model
 * TODO: sleep when under certain velotiy
 */
VG_STATIC void player_walk_physics(void)
{
   struct player_phys *phys = &player.phys;
   rigidbody *rbf = &player.collide_front,
             *rbb = &player.collide_back;

   m3x3_identity( player.collide_front.to_world );
   m3x3_identity( player.collide_back.to_world );

   v3_zero( phys->rb.w );
   q_axis_angle( phys->rb.q, (v3f){0.0f,1.0f,0.0f}, -player.angles[0] );

   rb_ct manifold[64];
   int len;

   v3f forward_dir = { sinf(player.angles[0]),0.0f,-cosf(player.angles[0]) };
   v3f right_dir = { -forward_dir[2], 0.0f, forward_dir[0] };

   v2f walk = { player.input_walkh->axis.value,
                player.input_walkv->axis.value };

   if( freecam )
      v2_zero( walk );
   
   if( v2_length2(walk) > 0.001f )
      v2_normalize_clamp( walk );

   if( phys->in_air )
   {
      player_walk_update_collision();
      rb_debug( rbf, 0xff0000ff );
      rb_debug( rbb, 0xff0000ff );

      /* allow player to accelerate a bit */
      v3f walk_3d;
      v3_muls( forward_dir, walk[1], walk_3d );
      v3_muladds( walk_3d, right_dir, walk[0], walk_3d );

      float current_vel = fabsf(v3_dot( walk_3d, phys->rb.v )),
            new_vel     = current_vel + VG_TIMESTEP_FIXED*k_air_accelerate,
            clamped_new = vg_clampf( new_vel, 0.0f, k_walkspeed ),
            vel_diff    = vg_maxf( 0.0f, clamped_new - current_vel );

      v3_muladds( phys->rb.v, right_dir,   walk[0] * vel_diff, phys->rb.v );
      v3_muladds( phys->rb.v, forward_dir, walk[1] * vel_diff, phys->rb.v );


      len = 0;
      len += rb_sphere_scene( rbf, &world.rb_geo, manifold+len );
      len += rb_sphere_scene( rbb, &world.rb_geo, manifold+len );
      rb_presolve_contacts( manifold, len );

      for( int i=0; i<len; i++ )
      {
         struct contact *ct = &manifold[i];
         if( v3_dot( ct->n, (v3f){0.0f,1.0f,0.0f} ) > 0.5f )
            phys->in_air = 0;
      }

      for( int j=0; j<5; j++ )
      {
         for( int i=0; i<len; i++ )
         {
            struct contact *ct = &manifold[i];
            
            /*normal */
            float vn = -v3_dot( phys->rb.v, ct->n );
            vn += ct->bias;

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

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

            v3_add( impulse, phys->rb.v, phys->rb.v );

            /* friction */
            for( int j=0; j<2; j++ )
            {
               float     f = k_friction * ct->norm_impulse,
                        vt = v3_dot( phys->rb.v, ct->t[j] ),
                    lambda = -vt;
               
               float temp = ct->tangent_impulse[j];
               ct->tangent_impulse[j] = vg_clampf( temp + lambda, -f, f );
               lambda = ct->tangent_impulse[j] - temp;

               v3_muladds( phys->rb.v, ct->t[j], lambda, phys->rb.v );
            }
         }
      }

      player_integrate();
   }
   else
   {
      player.walk = v2_length( walk );

      if( player.input_walk->button.value )
         v2_muls( walk, 0.5f, walk );

      v2_muls( walk, k_walkspeed * VG_TIMESTEP_FIXED, walk );

      v3f walk_apply;
      v3_zero( walk_apply );

      /* Do XY translation */
      v3_muladds( walk_apply, right_dir,   walk[0], walk_apply );
      v3_muladds( walk_apply, forward_dir, walk[1], walk_apply );
      v3_add( walk_apply, phys->rb.co, phys->rb.co );
      v3_divs( walk_apply, VG_TIMESTEP_FIXED, phys->rb.v );

      /* Directly resolve collisions */
      player_walk_update_collision();
      rb_debug( rbf, 0xffffff00 );
      rb_debug( rbb, 0xffffff00 );

      len = 0;
      len += rb_sphere_scene( rbf, &world.rb_geo, manifold+len );
      len += rb_sphere_scene( rbb, &world.rb_geo, manifold+len );

      v3f dt;
      v3_zero( dt );
      for( int j=0; j<3; j++ )
      {
         for( int i=0; i<len; i++ )
         {
            struct contact *ct = &manifold[i];

            float p   = vg_maxf( 0.0f, ct->p - 0.00f ),
                  cur = vg_clampf( v3_dot( ct->n, dt ), 0.0f, p );
            v3_muladds( dt, ct->n, (p - cur) * 0.333333333f, dt );
         }
      }
      v3_add( dt, phys->rb.co, phys->rb.co );

      if( len )
      {
         struct world_material *surface_mat = world_contact_material(manifold);
         player.surface_prop = surface_mat->info.surface_prop;
      }

      /* jump */
      if( player.input_jump->button.value )
      {
         phys->rb.v[1] = 5.0f;
         phys->in_air = 1;
         return;
      }

      /* Check if grounded by current manifold */
      phys->in_air = 1;
      for( int i=0; i<len; i++ )
      {
         struct contact *ct = &manifold[i];
         if( player_walk_surface_standable( ct->n ) )
            phys->in_air = 0;
      }
      
      /* otherwise... */
      if( phys->in_air )
         player_walk_stepdown();
      
#if 0
      /* if we've put us in the air, step down slowly */
      phys->in_air = 1;
      float max_dist = 0.3f,
            start_y = phys->rb.co[1];

      v3f pa, pb;
      v3_copy( phys->rb.co, pa );
      v3_muladds( pa, (v3f){0.0f,1.0f,0.0f}, -max_dist, pb );


      for( int j=0; j<8; j++ )
      {
         for( int i=0; i<len; i++ )
         {
            struct contact *ct = &manifold[i];
            if( v3_dot( ct->n, (v3f){0.0f,1.0f,0.0f} ) > 0.5f )
            {
               phys->in_air = 0;
               if( j == 0 )
                  return;

               v3f dt;
               v3_zero( dt );
               for( int j=0; j<3; j++ )
               {
                  for( int i=0; i<len; i++ )
                  {
                     struct contact *ct = &manifold[i];

                     float p   = vg_maxf( 0.0f, ct->p - 0.0025f ),
                           cur = vg_clampf( v3_dot( ct->n, dt ), 0.0f, p );
                     v3_muladds( dt, ct->n, (p - cur) * 0.333333333f, dt );
                  }
               }
               v3_add( dt, phys->rb.co, phys->rb.co );
               return;
            }
         }

         phys->rb.co[1] -= max_dist * 0.125f;

         player_walk_update_collision();
         len = 0;
         len += rb_sphere_scene( rbf, &world.rb_geo, manifold+len );
         len += rb_sphere_scene( rbb, &world.rb_geo, manifold+len );
      }
      
      /* Transitioning into air mode */
      phys->rb.co[1] = start_y;
#endif
   }
}

VG_STATIC void player_grind(void)
{
   struct player_phys *phys = &player.phys;

   v3f closest;
   int idx = bh_closest_point( world.grind_bh, phys->rb.co, closest, INFINITY );
   if( idx == -1 )
      return;

   struct grind_edge *edge = &world.grind_edges[ idx ];

   vg_line( phys->rb.co, closest, 0xff000000 );
   vg_line_cross( closest, 0xff000000, 0.3f );
   vg_line( edge->p0, edge->p1, 0xff000000 );

   v3f grind_delta;
   v3_sub( closest, phys->rb.co, grind_delta );
   
   float p = v3_dot( phys->rb.forward, grind_delta );
   v3_muladds( grind_delta, phys->rb.forward, -p, grind_delta );
   
   float a = vg_maxf( 0.0f, 4.0f-v3_dist2( closest, phys->rb.co ) );
   v3_muladds( phys->rb.v, grind_delta, a*0.2f, phys->rb.v );
}

VG_STATIC int player_update_grind_collision( rb_ct *contact )
{
   struct player_phys *phys = &player.phys;

   v3f p0, p1, c0, c1;
   v3_muladds( phys->rb.co, phys->rb.forward,  0.5f, p0 );
   v3_muladds( phys->rb.co, phys->rb.forward, -0.5f, p1 );
   v3_muladds( p0, phys->rb.up, 0.125f-0.15f, p0 );
   v3_muladds( p1, phys->rb.up, 0.125f-0.15f, p1 );

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

   
   vg_line( p0, p1, 0xff0000ff );

   if( closest_edge )
   {
      vg_line_cross( c0, 0xff000000, 0.1f );
      vg_line_cross( c1, 0xff000000, 0.1f );
      vg_line( c0, c1, 0xff000000 );

      v3f delta;
      v3_sub( c1, c0, delta );

      if( v3_dot( delta, phys->rb.up ) > 0.0001f )
      {
         contact->p = v3_length( delta );
         contact->type = k_contact_type_edge;
         contact->element_id = 0;
         v3_copy( c1, contact->co );
         contact->rba = &player.phys.rb;
         contact->rbb = &world.rb_geo;

         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 );

#if 0
         vg_info( "%f %f\n", v3_length( contact->n ), contact->p );
#endif

         return 1;
      }
      else
         return -1;
   }

   return 0;
}

/* Manifold must be able to hold at least 64 elements */
VG_STATIC int player_update_collision_manifold( rb_ct *manifold )
{
   struct player_phys *phys = &player.phys;

   phys->rise = vg_lerpf( phys->rise, phys->in_air? -0.25f: 0.0f, 
                          VG_TIMESTEP_FIXED );

   rigidbody *rbf = &player.collide_front,
             *rbb = &player.collide_back;

   m3x3_copy( phys->rb.to_world, player.collide_front.to_world );
   m3x3_copy( phys->rb.to_world, player.collide_back.to_world );
   
   player.air_blend = vg_lerpf( player.air_blend, phys->in_air, 0.1f );
   float h = player.air_blend*0.0f;

   m4x3_mulv( phys->rb.to_world, (v3f){0.0f,h,-k_board_length}, rbf->co );
   v3_copy( rbf->co, rbf->to_world[3] );
   m4x3_mulv( phys->rb.to_world, (v3f){0.0f,h, k_board_length}, rbb->co );
   v3_copy( rbb->co, rbb->to_world[3] );

   m4x3_invert_affine( rbf->to_world, rbf->to_local );
   m4x3_invert_affine( rbb->to_world, rbb->to_local );

   rb_update_bounds( rbf );
   rb_update_bounds( rbb );

   rb_debug( rbf, 0xff00ffff );
   rb_debug( rbb, 0xffffff00 );

   int len_f = 0,
       len_b = 0; 

   len_f = rb_sphere_scene( rbf, &world.rb_geo, manifold );
   rb_manifold_filter_coplanar( manifold, len_f, 0.05f );
   if( len_f > 1 )
   {
      rb_manifold_filter_backface( manifold, len_f );
      rb_manifold_filter_joint_edges( manifold, len_f, 0.05f );
      rb_manifold_filter_pairs( manifold, len_f, 0.05f );
   }
   int new_len_f = rb_manifold_apply_filtered( manifold, len_f );
   if( len_f && !new_len_f )
      len_f = 1;
   else
      len_f = new_len_f;
   
   rb_ct *man_b = &manifold[len_f];
   len_b = rb_sphere_scene( rbb, &world.rb_geo, man_b );
   rb_manifold_filter_coplanar( man_b, len_b, 0.05f );
   if( len_b > 1 )
   {
      rb_manifold_filter_backface( man_b, len_b );
      rb_manifold_filter_joint_edges( man_b, len_b, 0.05f );
      rb_manifold_filter_pairs( man_b, len_b, 0.05f );
   }
   int new_len_b = rb_manifold_apply_filtered( man_b, len_b );
   if( len_b && !new_len_b )
      len_b = 1;
   else
      len_b = new_len_b;
#if 0
   /* 
    * Preprocess collision points, and create a surface picture.
    * we want contacts that are within our 'capsule's internal line to be 
    * clamped so that they face the line and do not oppose, to stop the
    * player hanging up on stuff
    */
   for( int i=0; i<len; i++ )
   {
      v3f dfront, dback;
      v3_sub( manifold[i].co, rbf->co, dfront );
      v3_sub( manifold[i].co, rbb->co, dback );

      if( (v3_dot( dfront, phys->rb.forward ) < -0.02f) &&
          (v3_dot( dback,  phys->rb.forward ) > 0.02f))
      {
         float p = v3_dot( manifold[i].n, phys->rb.forward );
         v3_muladds( manifold[i].n, phys->rb.forward, -p, manifold[i].n );
         v3_normalize( manifold[i].n );
      }
   }
#endif

   return len_f + len_b;
}

VG_STATIC void player_adhere_ground( rb_ct *manifold, int len )
{
   struct player_phys *phys = &player.phys;
   int was_in_air = phys->in_air;

   v3f surface_avg;
   v3_zero( surface_avg );

   if( len == 0 )
   {
      phys->lift_frames ++;

      if( phys->lift_frames >= 8 )
         phys->in_air = 1;
   }
   else
   {
      for( int i=0; i<len; i++ )
         v3_add( surface_avg, manifold[i].n, surface_avg );
      v3_normalize( surface_avg );
      
      if( v3_dot( phys->rb.v, surface_avg ) > 0.7f )
      {
         phys->lift_frames ++;

         if( phys->lift_frames >= 8 )
            phys->in_air = 1;
      }
      else
      {
         phys->in_air = 0;
         phys->lift_frames = 0;
         v3f projected, axis;

         float const DOWNFORCE = -k_downforce*VG_TIMESTEP_FIXED;
         v3_muladds( phys->rb.v, phys->rb.up, DOWNFORCE, phys->rb.v );

         float d = v3_dot( phys->rb.forward, surface_avg );
         v3_muladds( surface_avg, phys->rb.forward, -d, projected );
         v3_normalize( projected );

         float angle = v3_dot( phys->rb.up, projected );
         v3_cross( phys->rb.up, projected, axis );

         v3f p0, p1;
         v3_add( phys->rb.co, projected, p0 );
         v3_add( phys->rb.co, phys->rb.up, p1 );
         vg_line( phys->rb.co, p0, 0xff00ff00 );
         vg_line( phys->rb.co, p1, 0xff000fff );

         if( fabsf(angle) < 0.999f )
         {
            v4f correction;
            q_axis_angle( correction, axis, 
                          acosf(angle)*4.0f*VG_TIMESTEP_FIXED );
            q_mul( correction, phys->rb.q, phys->rb.q );
         }
      }
   }

   if( !was_in_air && phys->in_air )
      player_start_air();
}

VG_STATIC void player_collision_response( rb_ct *manifold, int len )
{
   struct player_phys *phys = &player.phys;

   for( int j=0; j<5; j++ )
   {
      for( int i=0; i<len; i++ )
      {
         struct contact *ct = &manifold[i];
         
         v3f dv, delta;
         v3_sub( ct->co, phys->rb.co, delta ); 
         v3_cross( phys->rb.w, delta, dv );
         v3_add( phys->rb.v, dv, dv );

         float vn = -v3_dot( dv, ct->n );
         vn += ct->bias;

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

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

         if( fabsf(v3_dot( impulse, phys->rb.forward )) > 10.0f ||
             fabsf(v3_dot( impulse, phys->rb.up )) > 50.0f )
         {
            player_kill();
            return;
         }

         v3_add( impulse, phys->rb.v, phys->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( phys->rb.up, impulse ) * 0.8f,
               wx = v3_dot( phys->rb.right, impulse )*1.0f;

         v3_muladds( phys->rb.w, phys->rb.up, wy, phys->rb.w );
         v3_muladds( phys->rb.w, phys->rb.right, wx, phys->rb.w );
      }
   }
}

VG_STATIC void player_save_frame(void)
{
   player.phys_gate_frame = player.phys;
}

VG_STATIC void player_restore_frame(void)
{
   player.phys = player.phys_gate_frame;
   rb_update_transform( &player.phys.rb );
}

VG_STATIC void player_integrate(void)
{
   struct player_phys *phys = &player.phys;
   apply_gravity( phys->rb.v, VG_TIMESTEP_FIXED );
   v3_muladds( phys->rb.co, phys->rb.v, VG_TIMESTEP_FIXED, phys->rb.co );
}

VG_STATIC void player_do_motion(void)
{
   struct player_phys *phys = &player.phys;

   if( world.water.enabled )
   {
      if( (phys->rb.co[1] < 0.0f) && !player.is_dead )
      {
         audio_lock();
         audio_player_set_flags( &audio_player_extra, AUDIO_FLAG_SPACIAL_3D );
         audio_player_set_position( &audio_player_extra, phys->rb.co );
         audio_player_set_vol( &audio_player_extra, 20.0f );
         audio_player_playclip( &audio_player_extra, &audio_splash );
         audio_unlock();

         player_kill();
      }
   }

   v3f prevco;
   v3_copy( phys->rb.co, prevco );

   if( phys->on_board )
   {
      rb_ct manifold[72];
      int len = player_update_collision_manifold( manifold );
      int grind_col = player_update_grind_collision( &manifold[len] );

      static int _grind_col_pre = 0;

      if( grind_col )
      {
         phys->grind = 1;
         v3f up = { 0.0f, 1.0f, 0.0f };
         float angle = v3_dot( phys->rb.up, up );

         if( fabsf(angle) < 0.99f )
         {
            v3f axis; 
            v3_cross( phys->rb.up, up, axis );

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

         float const DOWNFORCE = -k_downforce*1.2f*VG_TIMESTEP_FIXED;
         v3_muladds( phys->rb.v, manifold[len].n, DOWNFORCE, phys->rb.v );
         m3x3_identity( phys->vr );
         m3x3_identity( phys->vr_pstep );

         if( !_grind_col_pre )
         {
            audio_lock();
            audio_player_set_flags( &audio_player_extra, 
                                    AUDIO_FLAG_SPACIAL_3D );
            audio_player_set_position( &audio_player_extra, phys->rb.co );
            audio_player_set_vol( &audio_player_extra, 20.0f );
            audio_player_playclip( &audio_player_extra, &audio_board[5] );
            audio_unlock();
         }
      }
      else
      {
         phys->grind = 0;
         player_adhere_ground( manifold, len );

         if( _grind_col_pre )
         {
            audio_lock();
            audio_player_set_flags( &audio_player_extra, 
                                    AUDIO_FLAG_SPACIAL_3D );
            audio_player_set_position( &audio_player_extra, phys->rb.co );
            audio_player_set_vol( &audio_player_extra, 20.0f );
            audio_player_playclip( &audio_player_extra, &audio_board[6] );
            audio_unlock();
         }
      }

      _grind_col_pre = grind_col;

      rb_presolve_contacts( manifold, len+ VG_MAX(0,grind_col) );
      player_collision_response( manifold, len+ VG_MAX(0,grind_col) );

      player_physics_control_passive();

      if( grind_col )
      {
         phys->in_air = 0;
         player_physics_control_grind();
      }
      else
      {
         if( phys->in_air )
            player_physics_control_air();
         else
            player_physics_control();
      }

      player_integrate();
   }
   else
      player_walk_physics();
   
   
   /* Real angular velocity integration */
   v3_lerp( phys->rb.w, (v3f){0.0f,0.0f,0.0f}, 0.125f*0.5f, phys->rb.w );
   if( v3_length2( phys->rb.w ) > 0.0f )
   {
      v4f rotation;
      v3f axis;
      v3_copy( phys->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, phys->rb.q, phys->rb.q );
   }

   /* Faux angular velocity */
   v4f rotate; 

   float lerpq = phys->in_air? 0.04f: 0.3f;
   phys->siY = vg_lerpf( phys->siY, phys->iY, lerpq );

   q_axis_angle( rotate, phys->rb.up, phys->siY );
   q_mul( rotate, phys->rb.q, phys->rb.q );
   phys->iY = 0.0f;

   /* 
    * Gate intersection, by tracing a line over the gate planes 
    */
   for( int i=0; i<world.gate_count; i++ )
   {
      struct route_gate *rg = &world.gates[i];
      teleport_gate *gate = &rg->gate;

      if( gate_intersect( gate, phys->rb.co, prevco ) )
      {
         m4x3_mulv( gate->transport, phys->rb.co, phys->rb.co );
         m3x3_mulv( gate->transport, phys->rb.v, phys->rb.v );
         m3x3_mulv( gate->transport, phys->vl, phys->vl );
         m3x3_mulv( gate->transport, phys->v_last, phys->v_last );
         m3x3_mulv( gate->transport, phys->m, phys->m );
         m3x3_mulv( gate->transport, phys->bob, phys->bob );

         /* Pre-emptively edit the camera matrices so that the motion vectors 
          * are correct */
         m4x3f transport_i;
         m4x4f transport_4;
         m4x3_invert_affine( gate->transport, transport_i );
         m4x3_expand( transport_i, transport_4 );
         m4x4_mul( main_camera.mtx.pv, transport_4, main_camera.mtx.pv );
         m4x4_mul( main_camera.mtx.v, transport_4, main_camera.mtx.v );

         v4f transport_rotation;
         m3x3_q( gate->transport, transport_rotation );
         q_mul( transport_rotation, phys->rb.q, phys->rb.q );
         
         world_routes_activate_gate( i );

         if( !phys->on_board )
         {
            v3f fwd_dir = {cosf(player.angles[0]),
                           0.0f,
                           sinf(player.angles[0])};
            m3x3_mulv( gate->transport, fwd_dir, fwd_dir );

            player.angles[0] = atan2f( fwd_dir[2], fwd_dir[0] );
         }
         
         player.rewind_length = 0;
         player.rewind_total_length = 0.0f;
         player.rewind_incrementer = 10000;
         player_save_frame();

         audio_lock();
         audio_play_oneshot( &audio_gate_pass, 1.0f );
         audio_unlock();
         break;
      }
   }
   
   rb_update_transform( &phys->rb );
}

VG_STATIC void player_freecam(void)
{
   player_mouseview();

   float movespeed = fc_speed * VG_TIMESTEP_FIXED;
   v3f lookdir = { 0.0f, 0.0f, -1.0f },
       sidedir = { 1.0f, 0.0f,  0.0f };
   
   m3x3_mulv( main_camera.transform, lookdir, lookdir );
   m3x3_mulv( main_camera.transform, sidedir, sidedir );
   
   static v3f move_vel = { 0.0f, 0.0f, 0.0f };

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

   v3_muladds( move_vel, sidedir,  movespeed*steer[0], move_vel );
   v3_muladds( move_vel, lookdir, -movespeed*steer[1], move_vel );

   v3_muls( move_vel, 0.7f, move_vel );
   v3_add( move_vel, player.camera_pos, player.camera_pos );
}

VG_STATIC int kill_player( int argc, char const *argv[] )
{
   player_kill();
   return 0;
}

VG_STATIC int reset_player( int argc, char const *argv[] )
{
   struct player_phys *phys = &player.phys;
   struct respawn_point *rp = NULL, *r;

   if( argc == 1 )
   {
      for( int i=0; i<world.spawn_count; i++ )
      {
         r = &world.spawns[i];
         if( !strcmp( r->name, argv[0] ) )
         {
            rp = r;
            break;
         }
      }

      if( !rp )
         vg_warn( "No spawn named '%s'\n", argv[0] );
   }

   if( !rp )
   {
      float min_dist = INFINITY;

      for( int i=0; i<world.spawn_count; i++ )
      {
         r = &world.spawns[i];
         float d = v3_dist2( r->co, phys->rb.co );
         
         vg_info( "Dist %s : %f\n", r->name, d );
         if( d < min_dist )
         {
            min_dist = d;
            rp = r;
         }
      }
   }

   if( !rp )
   {
      vg_error( "No spawn found\n" );
      vg_info( "Player position: %f %f %f\n", player.phys.rb.co[0],
                                              player.phys.rb.co[1],
                                              player.phys.rb.co[2] );
      vg_info( "Player velocity: %f %f %f\n", player.phys.rb.v[0],
                                              player.phys.rb.v[1],
                                              player.phys.rb.v[2] );

      if( !world.spawn_count )
         return 0;

      rp = &world.spawns[0];
   }

   player.is_dead = 0;

   m3x3f the_long_way;
   q_m3x3( rp->q, the_long_way );

   v3f delta = {1.0f,0.0f,0.0f};
   m3x3_mulv( the_long_way, delta, delta );
   
   if( !freecam )
   {
      player.angles[0] = atan2f( delta[0], -delta[2] ); 
      player.angles[1] = -asinf( delta[1] );
   }

   v4_copy( rp->q, phys->rb.q );
   v3_copy( rp->co, phys->rb.co );
   v3_zero( phys->rb.v );
   
   phys->vswitch = 1.0f;
   phys->slip_last = 0.0f;
   phys->in_air = 1;
   phys->on_board = 0;
   m3x3_identity( phys->vr );

   player.mdl.shoes[0] = 1;
   player.mdl.shoes[1] = 1;
   
   rb_update_transform( &phys->rb );
   player_save_frame();
   return 1;
}

#endif /* PLAYER_PHYSICS_H */