From: hgn <hgodden00@gmail.com>
Date: Wed, 15 Feb 2023 01:54:44 +0000 (+0000)
Subject: better? grinds
X-Git-Url: https://harrygodden.com/git/?a=commitdiff_plain;h=0a5ec40708e7d128511cac04f84d85055e6fc164;p=carveJwlIkooP6JGAAIwe30JlM.git

better? grinds
---

diff --git a/common.h b/common.h
index f9bcafa..82b0808 100644
--- a/common.h
+++ b/common.h
@@ -129,22 +129,28 @@ VG_STATIC float
    k_mmdecay               = 12.0f,
    k_spring_angular        = 1.0f,
 
-   k_spring_force          = 15.0f,
+   k_spring_force          = 130.0f,
    k_spring_dampener       = 5.0f,
 
    k_grind_spring          = 100.0f,
-   k_grind_dampener        = 6.0f,
+   k_grind_aligment        = 10.0f,
+   k_grind_dampener        = 40.0f,
+
    k_board_spring          = 100.0f,
    k_board_dampener        = 40.0f,
    k_manul_spring          = 200.0f,
    k_manul_dampener        = 30.0f,
    k_board_interia         = 8.0f,
 
+   k_grind_decayxy         = 30.0f,
+   k_grind_axel_min_vel    = 3.0f,
+   k_grind_axel_max_angle  = 0.97f, /* cosine(|a|) */
+   k_grind_max_friction    = 3.0f,
+
    k_board_length          = 0.45f,
    k_board_width           = 0.13f,
    k_board_end_radius      = 0.1f,
-   k_board_radius          = 0.07f;
-
+   k_board_radius          = 0.14f;    /* 0.07 */
 
 VG_STATIC float
    k_walkspeed             = 10.0f,
@@ -183,9 +189,14 @@ VG_STATIC void common_var_temp(void)
 
    VG_VAR_F32( k_grind_dampener );
    VG_VAR_F32( k_grind_spring );
+   VG_VAR_F32( k_grind_aligment );
    VG_VAR_F32( k_board_spring );
    VG_VAR_F32( k_board_dampener );
    VG_VAR_F32( k_board_interia );
+   VG_VAR_F32( k_grind_decayxy );
+   VG_VAR_F32( k_grind_axel_min_vel );
+   VG_VAR_F32( k_grind_axel_max_angle );
+   VG_VAR_F32( k_grind_max_friction );
 
    VG_VAR_F32( k_walkspeed );
    VG_VAR_F32( k_stopspeed );
diff --git a/maps_src/mp_gridmap.mdl b/maps_src/mp_gridmap.mdl
index d7ae80c..9240f93 100644
Binary files a/maps_src/mp_gridmap.mdl and b/maps_src/mp_gridmap.mdl differ
diff --git a/player.c b/player.c
index d86c8c8..6534523 100644
--- a/player.c
+++ b/player.c
@@ -230,7 +230,10 @@ VG_STATIC void player__pre_render( player_instance *player )
       skeleton_apply_pose( sk, res.pose, k_anim_apply_deffered_only );
       skeleton_apply_inverses( sk );
       skeleton_apply_transform( sk, transform );
+
+#if 0
       skeleton_debug( sk );
+#endif
    }
 
    if( _player_post_animate[ player->subsystem ] )
diff --git a/player_skate.c b/player_skate.c
index 7088cf1..01e3d7a 100644
--- a/player_skate.c
+++ b/player_skate.c
@@ -44,8 +44,6 @@ VG_STATIC int skate_collide_smooth( player_instance *player,
       man[i].rbb = NULL;
    }
 
-   return len;
-
    rb_manifold_filter_coplanar( man, len, 0.05f );
 
    if( len > 1 )
@@ -149,30 +147,29 @@ VG_STATIC int skate_grind_collide( player_instance *player, rb_ct *contact )
    return 0;
 }
 
-VG_STATIC int skate_grind_scansq( player_instance *player, v3f pos,
-                                  v3f result_co, v3f result_dir, v3f result_n )
+struct grind_info
+{
+   v3f co, dir, n;
+};
+
+VG_STATIC int skate_grind_scansq( player_instance *player, 
+                                  v3f pos, v3f dir, float r,
+                                  struct grind_info *inf )
 {
    v4f plane;
-   v3_copy( player->rb.v, plane );
+   v3_copy( dir, 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
+   vg_line_boxf( box, VG__BLACK );
 
    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 );
@@ -186,7 +183,6 @@ VG_STATIC int skate_grind_scansq( player_instance *player, v3f pos,
           centroid;
    }
    samples[48];
-
    int sample_count = 0;
 
    v2f support_min,
@@ -250,11 +246,14 @@ VG_STATIC int skate_grind_scansq( player_instance *player, v3f pos,
    if( sample_count < 2 )
       return 0;
 
-   v3f average_position,
+   v3f 
        average_direction,
        average_normal;
 
-   v3_zero( average_position );
+   v2f min_co, max_co;
+   v2_fill( min_co,  INFINITY );
+   v2_fill( max_co, -INFINITY );
+
    v3_zero( average_direction );
    v3_zero( average_normal );
 
@@ -288,11 +287,8 @@ VG_STATIC int skate_grind_scansq( player_instance *player, v3f pos,
              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 );
+         v2_minv( sj->co, min_co, min_co );
+         v2_maxv( sj->co, max_co, max_co );
          
          v3f n0, n1, dir;
          v3_copy( si->normal3, n0 );
@@ -321,25 +317,292 @@ VG_STATIC int skate_grind_scansq( player_instance *player, v3f pos,
       return 0;
 
    float div = 1.0f/(float)passed_samples;
-   v3_muls( average_position, div, average_position );
    v3_normalize( average_direction );
    v3_normalize( average_normal );
+
+   v2f average_coord;
+   v2_add( min_co, max_co, average_coord );
+   v2_muls( average_coord, 0.5f, average_coord );
+
+   v3_muls( support_axis, average_coord[0], inf->co );
+   inf->co[1] += average_coord[1];
+   v3_add( pos, inf->co, inf->co );
+   v3_copy( average_normal, inf->n );
+   v3_copy( average_direction, inf->dir );
+
+   vg_line_pt3( inf->co, 0.02f, VG__GREEN );
+   vg_line_arrow( inf->co, average_direction, 0.3f, VG__GREEN );
+   vg_line_arrow( inf->co, inf->n, 0.2f, VG__CYAN );
+
+   return passed_samples;
+}
+
+#if 0
+static inline void skate_grind_coordv2i( v2f co, v2i d )
+{
+   const float k_inv_res = 1.0f/0.01f;
+   d[0] = floorf( co[0] * k_inv_res );
+   d[1] = floorf( co[1] * k_inv_res );
+}
+
+static inline u32 skate_grind_hashv2i( v2i d )
+{
+   return (d[0] * 92837111) ^ (d[1] * 689287499);
+}
+
+static inline u32 skate_grind_hashv2f( v2f co )
+{
+   v2i d;
+   skate_grind_coordv2i( co, d );
+   return skate_grind_hashv2i( d );
+}
+
+VG_STATIC int skate_grind_scansq( player_instance *player, v3f pos,
+                                  v3f result_co, v3f result_dir, v3f result_n )
+{
+   v4f plane;
+   v3_copy( player->rb.v, plane );
+   v3_normalize( plane );
+   plane[3] = v3_dot( plane, pos );
+
+   boxf box;
+   float r = k_board_length;
+   v3_add( pos, (v3f){ r, r, r }, box[1] );
+   v3_sub( pos, (v3f){ r, r, r }, box[0] );
+
+   vg_line_boxf( box, VG__BLACK );
+
+   m4x3f mtx;
+   m3x3_copy( player->rb.to_world, mtx );
+   v3_copy( pos, mtx[3] );
+   
+   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;
+
+
+
+   /* spacial hashing */
+
+   const int k_hashmap_size = 128;
+   u32 hashmap[k_hashmap_size+1];
+   u32 entries[48];
+
+   for( int i=0; i<k_hashmap_size+1; i++ )
+      hashmap[i] = 0;
+
+   for( int i=0; i<sample_count; i++ )
+   {
+      u32 h = skate_grind_hashv2f( samples[i].co ) % k_hashmap_size;
+      hashmap[ h ] ++;
+   }
+
+   /* partial sums */
+   for( int i=0; i<k_hashmap_size; i++ )
+   {
+      hashmap[i+1] += hashmap[i];
+   }
+
+   /* trash compactor */
+   for( int i=0; i<sample_count; i++ )
+   {
+      u32 h = skate_grind_hashv2f( samples[i].co ) % k_hashmap_size;
+      hashmap[ h ] --;
+
+      entries[ hashmap[h] ] = i;
+   }
+
+
+   v3f 
+       average_direction,
+       average_normal;
+
+   v2f min_co, max_co;
+   v2_fill( min_co,  INFINITY );
+   v2_fill( max_co, -INFINITY );
+
+   v3_zero( average_direction );
+   v3_zero( average_normal );
+
+   int passed_samples = 0;
+   
+   for( int i=0; i<sample_count; i++ )
+   {
+      struct grind_sample *si, *sj;
+      si = &samples[i];
+
+      v2i start;
+      skate_grind_coordv2i( si->co, start );
+
+      v2i offsets[] = { {-1,-1},{ 0,-1},{ 1,-1},
+                        {-1, 0},{ 0, 0},{ 1, 0},
+                        {-1, 1},{ 0, 1},{ 1, 1} };
+
+      for( int j=0; j<vg_list_size(offsets); j++ )
+      {
+         v2i cell;
+         v2i_add( start, offsets[j], cell );
+         
+         u32 h = skate_grind_hashv2i( cell ) % k_hashmap_size;
+
+         int start = hashmap[ h ],
+             end   = hashmap[ h+1 ];
+
+         for( int k=start; k<end; k++ )
+         {
+            int idx = entries[ k ];
+            if( idx <= i )
+               continue;
+
+            sj = &samples[idx];
+
+            /* non overlapping */
+            if( v2_dist2( si->co, sj->co ) >= (0.01f*0.01f) )
+               continue;
+
+            /* not sharp angle */
+            if( v2_dot( si->normal, sj->normal ) >= 0.7f )
+               continue;
+
+            /* not convex */
+            v3f v0;
+            v3_sub( sj->centroid, si->centroid, v0 );
+            if( v3_dot( v0, si->normal3 ) >= 0.0f ||
+                v3_dot( v0, sj->normal3 ) <= 0.0f )
+               continue;
+
+            v2_minv( sj->co, min_co, min_co );
+            v2_maxv( sj->co, max_co, max_co );
+            
+            v3f n0, n1, dir;
+            v3_copy( si->normal3, n0 );
+            v3_copy( sj->normal3, n1 );
+            v3_cross( n0, n1, dir );
+            v3_normalize( dir );
+
+            /* make sure the directions all face a common hemisphere */
+            v3_muls( dir, vg_signf(v3_dot(dir,plane)), dir );
+            v3_add( average_direction, dir, average_direction );
+
+            if( si->normal3[1] > sj->normal3[1] )
+               v3_add( si->normal3, average_normal, average_normal );
+            else
+               v3_add( sj->normal3, average_normal, average_normal );
+
+            passed_samples ++;
+         }
+      }
+   }
+
+   if( !passed_samples )
+      return 0;
+
+   if( (v3_length2( average_direction ) <= 0.001f) ||
+       (v3_length2( average_normal ) <= 0.001f ) )
+      return 0;
+
+   float div = 1.0f/(float)passed_samples;
+   v3_normalize( average_direction );
+   v3_normalize( average_normal );
+
+   v2f average_coord;
+   v2_add( min_co, max_co, average_coord );
+   v2_muls( average_coord, 0.5f, average_coord );
+
+
+   v3_muls( support_axis, average_coord[0], result_co );
+   result_co[1] += average_coord[1];
+   v3_add( pos, result_co, result_co );
    
-   v3_add( pos, average_position, average_position );
-   vg_line_pt3( average_position, 0.02f, VG__GREEN );
+#if 0
+   vg_line_pt3( result_co, 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 );
+   v3_muladds( result_co, average_direction,  0.35f, p0 );
+   v3_muladds( result_co, average_direction, -0.35f, p1 );
    vg_line( p0, p1, VG__PINK );
+#endif
 
-   v3_copy( average_position, result_co );
    v3_copy( average_normal, result_n );
    v3_copy( average_direction, result_dir );
 
    return passed_samples;
 }
 
+#endif
+
 /*
  *
  * Prediction system
@@ -563,6 +826,7 @@ void player__approximate_best_trajectory( player_instance *player )
  * ------------------------------------------------
  */
 
+#if 0
 VG_STATIC void skate_apply_grind_model( player_instance *player,
                                         rb_ct *manifold, int len )
 {
@@ -639,6 +903,7 @@ VG_STATIC void skate_apply_grind_model( player_instance *player,
 #endif
    }
 }
+#endif
 
 /*
  * Air control, no real physics
@@ -647,9 +912,6 @@ 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 );
 
@@ -725,6 +987,7 @@ VG_STATIC void skate_apply_air_model( player_instance *player )
       limiter *= limiter;
       limiter = 1.0f-limiter;
 
+#if 0
       if( fabsf(angle) < 0.9999f )
       {
          v4f correction;
@@ -732,21 +995,18 @@ VG_STATIC void skate_apply_air_model( player_instance *player )
                         acosf(angle)*(1.0f-limiter)*2.0f*VG_TIMESTEP_FIXED );
          q_mul( correction, player->rb.q, player->rb.q );
       }
+#endif
    }
 
    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 );
 }
 
+#if 0
 VG_STATIC void skate_get_board_points( player_instance *player,
                                        v3f front, v3f back )
 {
@@ -756,7 +1016,9 @@ VG_STATIC void skate_get_board_points( player_instance *player,
    m4x3_mulv( player->rb.to_world, pos_front, front );
    m4x3_mulv( player->rb.to_world, pos_back,  back );
 }
+#endif
 
+#if 0
 /*
  * Casts and pushes a sphere-spring model into the world
  */
@@ -806,6 +1068,7 @@ VG_STATIC int skate_simulate_spring( player_instance *player,
       return 0;
    }
 }
+#endif
 
 
 /* 
@@ -818,16 +1081,9 @@ VG_STATIC void skate_apply_interface_model( player_instance *player,
 {
    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 */
+
+#if 0
    v3f spring0, spring1;
 
    skate_get_board_points( player, spring1, spring0 );
@@ -909,6 +1165,7 @@ VG_STATIC void skate_apply_interface_model( player_instance *player,
 #endif
       }
    }
+#endif
 }
 
 VG_STATIC int player_skate_trick_input( player_instance *player );
@@ -971,8 +1228,7 @@ VG_STATIC void skate_apply_trick_model( player_instance *player )
    }
    else
    {
-      if( (s->state.lift_frames == 0) 
-          && (v3_length2(s->state.trick_vel) >= 0.0001f ) &&
+      if( (v3_length2(s->state.trick_vel) >= 0.0001f ) &&
           s->state.trick_time > 0.2f)
       {
          player__dead_transition( player );
@@ -1005,6 +1261,39 @@ VG_STATIC void skate_apply_grab_model( player_instance *player )
    s->state.grabbing = vg_lerpf( s->state.grabbing, grabt, 8.4f*k_rb_delta );
 }
 
+VG_STATIC void skate_apply_steering_model( player_instance *player )
+{
+   struct player_skate *s = &player->_skate;
+
+   /* Steering */
+   float 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 rate = 26.0f;
+
+   if( s->state.activity == k_skate_activity_air )
+   {
+      rate = 6.0f * fabsf(steer_scaled);
+   }
+
+   else if( s->state.activity >= k_skate_activity_grind_any )
+   {
+      rate *= fabsf(steer_scaled);
+   }
+
+   float current  = v3_dot( player->rb.to_world[1], player->rb.w ),
+         addspeed = (steer_scaled * -1.0f) - current,
+         maxaccel = rate * k_rb_delta,
+         accel    = vg_clampf( addspeed, -maxaccel, maxaccel );
+
+   v3_muladds( player->rb.w, player->rb.to_world[1], accel, player->rb.w );
+}
+
 /*
  * Computes friction and surface interface model
  */
@@ -1012,9 +1301,6 @@ 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
@@ -1062,41 +1348,20 @@ VG_STATIC void skate_apply_friction_model( player_instance *player )
 
    /* 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;
+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 )
+   if( s->state.activity == k_skate_activity_air )
+   {
       s->state.charging_jump = 0;
+      return;
+   }
 
    if( s->state.charging_jump )
    {
@@ -1107,14 +1372,11 @@ VG_STATIC void skate_apply_jump_model( player_instance *player )
    }
    else
    {
-      s->state.jump_charge -= k_jump_charge_speed * VG_TIMESTEP_FIXED;
+      s->state.jump_charge -= k_jump_charge_speed * k_rb_delta;
    }
 
    s->state.jump_charge = vg_clampf( s->state.jump_charge, 0.0f, 1.0f );
 
-   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) )
    {
@@ -1135,17 +1397,19 @@ VG_STATIC void skate_apply_jump_model( player_instance *player )
       v3_muladds( player->rb.v, jumpdir, force, player->rb.v );
       s->state.jump_charge = 0.0f;
       s->state.jump_time = vg.time;
+      s->state.activity = k_skate_activity_air;
 
       v2f steer = { player->input_js1h->axis.value,
                     player->input_js1v->axis.value };
       v2_normalize_clamp( steer );
 
+
 #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 ++;
+#endif
 
       /* FIXME audio events */
 #if 0
@@ -1236,131 +1500,28 @@ VG_STATIC void skate_apply_cog_model( player_instance *player )
    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);
+   float decay_rate = 1.0f - (k_rb_delta * 3.0f),
+         decay_rate_y = 1.0f;
 
-#if 0
-   if( s->state.activity == k_skate_activity_air )
+   if( s->state.activity >= k_skate_activity_grind_any )
    {
-      float dist = 1.0f-(s->land_dist/4.0f);
-      decay_rate = 0.5f * vg_maxf( dist*dist, 0.0f );
+      decay_rate = 1.0f-vg_lerpf( 3.0f, 20.0f, s->grind_strength ) * k_rb_delta;
+      decay_rate_y = decay_rate;
    }
-#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] ),
+         wy = v3_dot( player->rb.w, player->rb.to_world[1] ) * decay_rate_y,
          wz = v3_dot( player->rb.w, player->rb.to_world[2] ) * decay_rate;
 
    v3_muls(                  player->rb.to_world[0], wx, player->rb.w );
    v3_muladds( player->rb.w, player->rb.to_world[1], wy, player->rb.w );
    v3_muladds( player->rb.w, player->rb.to_world[2], wz, player->rb.w );
 
-#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 );
 }
@@ -1405,7 +1566,7 @@ VG_STATIC void player__skate_pre_update( player_instance *player )
    }
 
    int trick_id; 
-   if( (s->state.lift_frames > 0) &&
+   if( (s->state.activity == k_skate_activity_air) && 
        (trick_id = player_skate_trick_input( player )) )
    {
       if( (vg.time - s->state.jump_time) < 0.1f )
@@ -1428,29 +1589,566 @@ VG_STATIC void player__skate_pre_update( player_instance *player )
          }
       }
    }
-}
+}
+
+VG_STATIC void player__skate_post_update( player_instance *player )
+{
+   struct player_skate *s = &player->_skate;
+
+#if 0
+   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 );
+#endif
+}
+
+/*
+ * truck alignment model at ra(local)
+ * returns 1 if valid surface:
+ *             surface_normal will be filled out with an averaged normal vector
+ *             axel_dir will be the direction from left to right wheels
+ *
+ * returns 0 if no good surface found
+ */
+VG_STATIC 
+int skate_compute_surface_alignment( player_instance *player,
+                                     v3f ra, u32 colour,
+                                     v3f surface_normal, v3f axel_dir )
+{
+   struct player_skate *s = &player->_skate;
+
+   v3f truck, left, right;
+   m4x3_mulv( player->rb.to_world, ra, truck );
+   v3_muladds( truck, player->rb.to_world[0], -k_board_width, left  );
+   v3_muladds( truck, player->rb.to_world[0],  k_board_width, right );
+   
+   vg_line( left, right, colour );
+
+   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;
+
+   if( res_r )
+      if( v3_dot( ray_r.normal, player->rb.to_world[1] ) < 0.7071f )
+         res_r = 0;
+
+   v3f v0;
+   v3f midpoint;
+   v3f tangent_average;
+   v3_muladds( truck, player->rb.to_world[1], -k_board_radius, midpoint );
+   v3_zero( tangent_average );
+
+   if( res_l || res_r )
+   {
+      v3f p0, p1, t;
+      v3_copy( midpoint, p0 );
+      v3_copy( midpoint, p1 );
+
+      if( res_l ) 
+      {
+         v3_copy( ray_l.pos, p0 );
+         v3_cross( ray_l.normal, player->rb.to_world[0], t );
+         v3_add( t, tangent_average, tangent_average );
+      }
+      if( res_r )
+      {
+         v3_copy( ray_r.pos, p1 );
+         v3_cross( ray_r.normal, player->rb.to_world[0], t );
+         v3_add( t, tangent_average, tangent_average );
+      }
+
+      v3_sub( p1, p0, v0 );
+      v3_normalize( v0 );
+   }
+   else
+   {
+      /* fallback: use the closes point to the trucks */
+      v3f closest;
+      int idx = bh_closest_point( world.geo_bh, midpoint, closest, 0.1f );
+
+      if( idx != -1 )
+      {
+         u32 *tri = &world.scene_geo->arrindices[ idx * 3 ];
+         v3f verts[3];
+
+         for( int j=0; j<3; j++ )
+            v3_copy( world.scene_geo->arrvertices[ tri[j] ].co, verts[j] );
+
+         v3f vert0, vert1, n;
+         v3_sub( verts[1], verts[0], vert0 );
+         v3_sub( verts[2], verts[0], vert1 );
+         v3_cross( vert0, vert1, n );
+         v3_normalize( n );
+
+         if( v3_dot( n, player->rb.to_world[1] ) < 0.3f )
+            return 0;
+
+         v3_cross( n, player->rb.to_world[2], v0 );
+         v3_muladds( v0, player->rb.to_world[2],
+                     -v3_dot( player->rb.to_world[2], v0 ), v0 );
+         v3_normalize( v0 );
+
+         v3f t;
+         v3_cross( n, player->rb.to_world[0], t );
+         v3_add( t, tangent_average, tangent_average );
+      }
+      else
+         return 0;
+   }
+
+   v3_muladds( truck, v0,  k_board_width, right );
+   v3_muladds( truck, v0, -k_board_width, left );
+
+   vg_line( left, right, VG__WHITE );
+
+   v3_normalize( tangent_average );
+   v3_cross( v0, tangent_average, surface_normal );
+   v3_copy( v0, axel_dir );
+
+   return 1;
+}
+
+VG_STATIC void skate_weight_distribute( player_instance *player )
+{
+   struct player_skate *s = &player->_skate;
+   v3_zero( s->weight_distribution );
+
+   int reverse_dir = v3_dot( player->rb.to_world[2], player->rb.v ) < 0.0f?1:-1;
+
+   if( s->state.manual_direction == 0 )
+   {
+      if( (player->input_js1v->axis.value > 0.7f) && 
+          (s->state.activity == k_skate_activity_ground) &&
+          (s->state.jump_charge <= 0.01f) )
+         s->state.manual_direction = reverse_dir;
+   }
+   else
+   {
+      if( player->input_js1v->axis.value < 0.1f )
+      {
+         s->state.manual_direction = 0;
+      }
+      else
+      {
+         if( reverse_dir != s->state.manual_direction )
+         {
+#if 0
+            player__dead_transition( player );
+#endif
+            return;
+         }
+      }
+   }
+
+   if( s->state.manual_direction )
+   {
+      float amt = vg_minf( player->input_js1v->axis.value * 8.0f, 1.0f );
+      s->weight_distribution[2] = k_board_length * amt * 
+                                          (float)s->state.manual_direction;
+   }
+
+   /* TODO: Fall back on land normal */
+   /* TODO: Lerp weight distribution */
+   /* TODO: Can start manual only if not charge jump */
+   if( s->state.manual_direction )
+   {
+      v3f plane_z;
+
+      m3x3_mulv( player->rb.to_world, s->weight_distribution, plane_z );
+      v3_negate( plane_z, plane_z );
+
+      v3_muladds( plane_z, s->surface_picture,
+                  -v3_dot( plane_z, s->surface_picture ), plane_z );
+      v3_normalize( plane_z );
+
+      v3_muladds( plane_z, s->surface_picture, 0.3f, plane_z );
+      v3_normalize( plane_z );
+
+      v3f p1;
+      v3_muladds( player->rb.co, plane_z, 1.5f, p1 );
+      vg_line( player->rb.co, p1, VG__GREEN );
+
+      v3f refdir;
+      v3_muls( player->rb.to_world[2], -(float)s->state.manual_direction,
+               refdir );
+
+      rb_effect_spring_target_vector( &player->rb, refdir, plane_z,
+                                       k_manul_spring, k_manul_dampener,
+                                       s->substep_delta );
+   }
+}
+
+VG_STATIC void skate_adjust_up_direction( player_instance *player )
+{
+   struct player_skate *s = &player->_skate;
+
+   if( s->state.activity == k_skate_activity_ground )
+   {
+      v3f target;
+      v3_copy( s->surface_picture, target );
+
+      target[1] += 2.0f * s->surface_picture[1];
+      v3_normalize( target );
+
+      v3_lerp( s->state.up_dir, target,
+               8.0f * s->substep_delta, s->state.up_dir );
+   }
+   else if( s->state.activity == k_skate_activity_air )
+   {
+      v3_lerp( s->state.up_dir, player->rb.to_world[1],
+               8.0f * s->substep_delta, s->state.up_dir );
+   }
+   else
+   {
+      /* FIXME UNDEFINED! */
+      vg_warn( "Undefined up target!\n" );
+
+      v3_lerp( s->state.up_dir, (v3f){0.0f,1.0f,0.0f},
+               12.0f * s->substep_delta, s->state.up_dir );
+   }
+}
+
+VG_STATIC int skate_point_visible( v3f origin, v3f target )
+{
+   v3f dir;
+   v3_sub( target, origin, dir );
+   
+   ray_hit ray;
+   ray.dist = v3_length( dir );
+   v3_muls( dir, 1.0f/ray.dist, dir );
+   ray.dist -= 0.025f;
+
+   if( ray_world( origin, dir, &ray ) )
+      return 0;
+
+   return 1;
+}
+
+VG_STATIC void skate_grind_orient( struct grind_info *inf, m3x3f mtx )
+{
+   /* TODO: Is N and Dir really orthogonal? */
+   v3_copy( inf->dir, mtx[0] );
+   v3_copy( inf->n, mtx[1] );
+   v3_cross( mtx[0], mtx[1], mtx[2] );
+}
+
+VG_STATIC void skate_grind_truck_apply( player_instance *player,
+                                        v3f grind_co, struct grind_info *inf,
+                                        float strength )
+{
+   struct player_skate *s = &player->_skate;
+
+   v3f delta;
+   v3_sub( inf->co, grind_co, delta );
+
+   m3x3f mtx, mtx_inv;
+   skate_grind_orient( inf, mtx );
+   m3x3_transpose( mtx, mtx_inv );
+
+   /* decay 'force' */
+   v3f v_grind;
+   m3x3_mulv( mtx_inv, player->rb.v, v_grind );
+
+   float decay = 1.0f - ( k_rb_delta * k_grind_decayxy * strength );
+   v3_mul( v_grind, (v3f){ 1.0f, decay, decay }, v_grind );
+   m3x3_mulv( mtx, v_grind, player->rb.v );
+
+   /* spring force */
+   v3_muladds( player->rb.v, delta, k_spring_force*strength*k_rb_delta, 
+               player->rb.v );
+
+   /* friction force */
+   float a        = 1.0f-fabsf( v3_dot( player->rb.to_world[2], inf->dir ) ),
+         dir      = vg_signf( v3_dot( player->rb.v, inf->dir ) ),
+         F        = a * -dir * k_grind_max_friction;
+
+   v3_muladds( player->rb.v, inf->dir, F*k_rb_delta*strength, player->rb.v );
+
+   /* orientation */
+   rb_effect_spring_target_vector( &player->rb, player->rb.to_world[1],
+                                    inf->n,
+                                    k_grind_spring, 
+                                    k_grind_dampener,
+                                    k_rb_delta );
+   vg_line_arrow( player->rb.co, inf->n, 1.0f, VG__GREEN );
+
+   /* TODO: This was a nice idea, but we should just apply steering to the 
+    *       target vector instead of this strange feedback loop thing! */
+   v3f target_fwd;
+   m3x3_mulv( mtx, s->grind_vec, target_fwd );
+
+   rb_effect_spring_target_vector( &player->rb, player->rb.to_world[2],
+                                    target_fwd,
+                                    k_grind_spring*strength, 
+                                    k_grind_dampener*strength,
+                                    k_rb_delta );
+
+   vg_line_arrow( player->rb.co, target_fwd, 1.0f, VG__YELOW );
+
+   v3f new_target;
+   m3x3_mulv( mtx_inv, player->rb.to_world[2], new_target );
+   v3_lerp( s->grind_vec, new_target, k_rb_delta * 0.1f, s->grind_vec );
+
+   s->grind_strength = strength;
+
+   /* Fake contact */
+   struct grind_limit *limit = &s->limits[ s->limit_count ++ ];
+   m4x3_mulv( player->rb.to_local, grind_co, limit->ra );
+   m3x3_mulv( player->rb.to_local, inf->n, limit->n );
+   limit->p = 0.0f;
+}
+
+VG_STATIC int skate_grind_truck_singular( player_instance *player, float sign )
+{
+   struct grind_info inf;
+
+   v3f wheel_co = { 0.0f, 0.0f,            sign * k_board_length },
+       grind_co = { 0.0f, -k_board_radius, sign * k_board_length };
+
+   m4x3_mulv( player->rb.to_world, wheel_co, wheel_co );
+   m4x3_mulv( player->rb.to_world, grind_co, grind_co );
+
+   /* Exit condition: lost grind tracking */
+   if( !skate_grind_scansq( player, grind_co, player->rb.v, 0.3f, &inf ) )
+      return 0;
+
+   /* Exit condition: cant see grind target directly */
+   if( !skate_point_visible( wheel_co, inf.co ) )
+      return 0;
+
+   /* Exit condition: minimum velocity not reached, but allow a bit of error */
+   float dv   = fabsf(v3_dot( player->rb.v, inf.dir )),
+         minv = k_grind_axel_min_vel*0.8f;
+
+   if( dv < minv )
+      return 0;
+
+   float t = vg_clampf( (dv-minv)/(k_grind_axel_min_vel-minv), 0.0f, 1.0f );
+   skate_grind_truck_apply( player, grind_co, &inf, t );
+   return 1;
+}
+
+VG_STATIC int skate_truck_entry_condition( player_instance *player, float sign )
+{
+   struct player_skate *s = &player->_skate;
+   struct grind_info inf;
+
+   /* TODO: Trash compactor this */
+   v3f ra = { 0.0f, -k_board_radius, sign * k_board_length };
+
+   v3f raw, wsp;
+   m3x3_mulv( player->rb.to_world, ra, raw );
+   v3_add( player->rb.co, raw, wsp );
+
+   if( skate_grind_scansq( player,
+                           wsp, player->rb.v, 0.3, 
+                           &inf ) )
+   {
+      if( fabsf(v3_dot( player->rb.v, inf.dir )) < k_grind_axel_min_vel )
+         return 0;
+
+      /* velocity should be at least 60% aligned */
+      v3f pv, axis;
+      v3_cross( inf.n, inf.dir, axis );
+      v3_muladds( player->rb.v, inf.n, -v3_dot( player->rb.v, inf.n ), pv );
+      
+      if( v3_length2( pv ) < 0.0001f )
+         return 0;
+      v3_normalize( pv );
+
+      if( fabsf(v3_dot( pv, inf.dir )) < k_grind_axel_max_angle )
+         return 0;
+
+      
+      v3f local_co, local_dir, local_n;
+      m4x3_mulv( player->rb.to_local, inf.co,  local_co );
+      m3x3_mulv( player->rb.to_local, inf.dir, local_dir );
+      m3x3_mulv( player->rb.to_local, inf.n,   local_n );
+
+      v2f delta = { local_co[0], local_co[2] - k_board_length*sign };
+
+      float truck_height = -(k_board_radius+0.03f);
+
+      v3f rv;
+      v3_cross( player->rb.w, raw, rv );
+      v3_add( player->rb.v, rv, rv );
+
+      if( (local_co[1] >= truck_height) &&
+          (v2_length2( delta ) <= k_board_radius*k_board_radius) &&
+          (v3_dot( rv, inf.n ) < 0.1f) )
+      {
+         m3x3f mtx;
+         skate_grind_orient( &inf, mtx );
+         m3x3_transpose( mtx, mtx );
+         m3x3_mulv( mtx, player->rb.to_world[2], s->grind_vec );
+
+         skate_grind_truck_apply( player, wsp, &inf, 1.0f );
+         return 1;
+      }
+   }
+
+   return 0;
+}
+
+VG_STATIC enum skate_activity skate_availible_grind( player_instance *player )
+{
+   struct player_skate *s = &player->_skate;
+
+   /* 
+    * BOARDSLIDE
+    * ------------------------------------
+    */
+
+   struct grind_info grind_center;
+   if( skate_grind_scansq( player, 
+                           player->rb.co, 
+                           player->rb.to_world[0], k_board_length,
+                           &grind_center ) )
+   {
+      v3f local_co, local_dir, local_n;
+      m4x3_mulv( player->rb.to_local, grind_center.co, local_co );
+      m3x3_mulv( player->rb.to_local, grind_center.dir, local_dir );
+      m3x3_mulv( player->rb.to_local, grind_center.n, local_n );
+
+      if( (fabsf(local_co[2]) <= k_board_length) &&   /* within wood area */
+          (local_co[1] >= 0.0f) &&                    /* at deck level */
+          (fabsf(local_dir[0]) >= 0.5f) )             /* perpendicular to us */
+      {
+         /* compute position on center line */
+
+         v3f intersection;
+         v3_muladds( local_co, local_dir, local_co[0]/-local_dir[0], 
+                     intersection );
+         v3_copy( intersection, s->weight_distribution );
+
+
+         /* TODO: alignment & strengths should be proportional to speed */
+         /*       dont apply correction in connecting velocities */
+         /*       friciton */
+
+         v3f ideal_v, diff;
+         v3_muls( grind_center.dir, 
+                  v3_dot( player->rb.v, grind_center.dir ), ideal_v );
+
+         v3_sub( ideal_v, player->rb.v, diff );
+         v3_muladds( player->rb.v, diff, k_grind_aligment * k_rb_delta,
+                     player->rb.v );
+
+
+         /* direction alignment */
+         v3f dir, perp;
+         v3_cross( local_dir, local_n, perp );
+         v3_muls( local_dir, vg_signf(local_dir[0]), dir );
+         v3_muls( perp, vg_signf(perp[2]), perp );
+
+         m3x3_mulv( player->rb.to_world, dir, dir );
+         m3x3_mulv( player->rb.to_world, perp, perp );
+
+         rb_effect_spring_target_vector( &player->rb, player->rb.to_world[0],
+                                          dir, 
+                                          k_grind_spring, k_grind_dampener,
+                                          k_rb_delta );
+
+         rb_effect_spring_target_vector( &player->rb, player->rb.to_world[2],
+                                          perp,
+                                          k_grind_spring, k_grind_dampener,
+                                          k_rb_delta );
+
+         vg_line_arrow( player->rb.co, dir, 0.5f, VG__GREEN );
+         vg_line_arrow( player->rb.co, perp, 0.5f, VG__BLUE );
+
+         return k_skate_activity_grind_boardslide;
+      }
+   }
 
-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++ )
+   if( s->state.activity == k_skate_activity_grind_back50 )
    {
-      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 );
+      int result = skate_grind_truck_singular( player,   1.0f ),
+          front  = skate_truck_entry_condition( player, -1.0f );
 
-      vg_line_cross( p->log[p->log_length-1], p->colour, 0.25f );
+      const enum skate_activity table[] =
+      {                                   /* result  | front */
+         k_skate_activity_undefined,      /* 0         0     */
+         k_skate_activity_grind_front50,  /* 0         1     */
+         k_skate_activity_grind_back50,   /* 1         0     */
+         k_skate_activity_grind_5050      /* 1         1     */
+      };
 
-      v3f p1;
-      v3_add( p->log[p->log_length-1], p->n, p1 );
-      vg_line( p->log[p->log_length-1], p1, 0xffffffff );
+      return table[ result<<1 | front ];
+   }
+   else if( s->state.activity == k_skate_activity_grind_front50 )
+   {
+      int result = skate_grind_truck_singular( player,   -1.0f ),
+          back   = skate_truck_entry_condition( player,   1.0f );
 
-      vg_line_pt3( p->apex, 0.02f, 0xffffffff );
+      const enum skate_activity table[] =
+      {                                   /* result  | back  */
+         k_skate_activity_undefined,      /* 0         0     */
+         k_skate_activity_grind_back50,   /* 0         1     */
+         k_skate_activity_grind_front50,  /* 1         0     */
+         k_skate_activity_grind_5050      /* 1         1     */
+      };
+
+      return table[ result<<1 | back ];
+   }
+   else if( s->state.activity == k_skate_activity_grind_5050 )
+   {
+      /* FIXME */
+      return k_skate_activity_grind_back50;
    }
+   else
+   {
+      int front = skate_truck_entry_condition( player,  -1.0f ),
+          back  = skate_truck_entry_condition( player,   1.0f );
 
-   vg_line_pt3( s->state.apex, 0.200f, 0xff0000ff );
-   vg_line_pt3( s->state.apex, 0.201f, 0xff00ffff );
+      const enum skate_activity table[] =
+      {                                   /* front   | back  */
+         k_skate_activity_undefined,      /* 0         0     */
+         k_skate_activity_grind_back50,   /* 0         1     */
+         k_skate_activity_grind_front50,  /* 1         0     */
+         k_skate_activity_grind_5050      /* 1         1     */
+      };
+
+      return table[ front<<1 | back ];
+   }
+
+   return 0;
+}
+
+VG_STATIC void skate_grind_boardslide( player_instance *player )
+{
+   
 }
 
 VG_STATIC void player__skate_update( player_instance *player )
@@ -1479,13 +2177,13 @@ VG_STATIC void player__skate_update( player_instance *player )
    {
       { 
          { 0.0f, 0.0f,    -k_board_length }, 
-         .radius = 0.07f, 
+         .radius = k_board_radius,
          .apply_angular = 1,
          .colour = VG__RED
       },
       { 
          { 0.0f, 0.0f,     k_board_length }, 
-         .radius = 0.07f,
+         .radius = k_board_radius,
          .apply_angular = 1,
          .colour = VG__GREEN
       },
@@ -1504,240 +2202,77 @@ VG_STATIC void player__skate_update( player_instance *player )
    };
 
    const int k_wheel_count = 2;
-#if 0
-   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
-   }
-#endif
 
    s->substep = k_rb_delta;
    s->substep_delta = s->substep;
-   int substep_count = 0;
-
-
+   s->limit_count = 0;
 
+   int substep_count = 0;
 
+   v3_zero( s->surface_picture );
 
-   /* 
-    * Phase 2: Truck alignment (spring/dampener model)
-    *          it uses the first two colliders as truck positions
-    * --------------------------------------------------------------------------
-    */
+   for( int i=0; i<k_wheel_count; i++ )
+      wheels[i].state = k_collider_state_default;
 
-   v3f surface_picture;
-   v3_zero( surface_picture );
-   
-   for( int i=0; i<2; i++ )
+   /* check if we can enter or continue grind */
+   enum skate_activity grindable_activity = skate_availible_grind( player );
+   if( grindable_activity != k_skate_activity_undefined )
    {
-      if( wheels[i].state == k_collider_state_disabled )
-         continue;
-
-      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_r.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 vert0, vert1, n;
-            v3_sub( verts[1], verts[0], vert0 );
-            v3_sub( verts[2], verts[0], vert1 );
-            v3_cross( vert0, vert1, n );
-            v3_normalize( n );
-
-            if( v3_dot( n, player->rb.to_world[1] ) < 0.3f )
-               continue;
-
-            v3_cross( n, player->rb.to_world[2], v0 );
-            v3_muladds( v0, player->rb.to_world[2],
-                        -v3_dot( player->rb.to_world[2], v0 ), v0 );
-            v3_normalize( v0 );
-         }
-         else
-            continue;
-      }
-
-      v3_muladds( truck, v0,  k_board_width, right );
-      v3_muladds( truck, v0, -k_board_width, left );
-
-      vg_line( left, right, VG__WHITE );
-
-      rb_effect_spring_target_vector( &player->rb, player->rb.to_world[0], v0,
-                                       k_board_spring, k_board_dampener,
-                                       s->substep_delta );
+      s->state.activity = grindable_activity;
+      goto grinding;
    }
 
-   /* 
-    * 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.jump_charge <= 0.01f) )
-         s->state.manual_direction = reverse_dir;
-   }
-   else
+   int contact_count = 0;
+   for( int i=0; i<2; i++ )
    {
-      if( player->input_js1v->axis.value < 0.1f )
-      {
-         s->state.manual_direction = 0;
-      }
-      else
+      v3f normal, axel;
+      if( skate_compute_surface_alignment( player, wheels[i].pos, 
+                                           wheels[i].colour, normal, axel ) )
       {
-         if( reverse_dir != s->state.manual_direction )
-         {
-            player__dead_transition( player );
-            return;
-         }
-      }
-   }
+         rb_effect_spring_target_vector( &player->rb, player->rb.to_world[0],
+                                          axel,
+                                          k_board_spring, k_board_dampener,
+                                          s->substep_delta );
 
-   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;
+         v3_add( normal, s->surface_picture, s->surface_picture );
+         contact_count ++;
+      }
    }
 
-   if( v3_length2( surface_picture ) > 0.001f )
+   if( contact_count )
    {
-      v3_normalize( surface_picture );
-
-      v3f target;
-      v3_copy( surface_picture, target );
+      s->state.activity = k_skate_activity_ground;
+      v3_normalize( s->surface_picture );
 
-      target[1] += 2.0f * surface_picture[1];
-      v3_normalize( target );
-
-      v3_lerp( s->state.up_dir, target,
-               8.0f * s->substep_delta, s->state.up_dir );
+      skate_apply_friction_model( player );
+      skate_weight_distribute( player );
+      skate_apply_pump_model( player );
    }
    else
    {
-      v3_lerp( s->state.up_dir, player->rb.to_world[1],
-               8.0f * s->substep_delta, s->state.up_dir );
+      s->state.activity = k_skate_activity_air;
+      skate_apply_air_model( player );
    }
 
+grinding:;
 
-   /* TODO: Fall back on land normal */
-   /* TODO: Lerp weight distribution */
-   /* TODO: Can start manual only if not charge jump */
-   if( v3_length2( surface_picture ) > 0.001f && 
-       v3_length2( weight ) > 0.001f &&
-       s->state.manual_direction )
+   if( s->state.activity == k_skate_activity_grind_back50 )
+      wheels[1].state = k_collider_state_disabled;
+   if( s->state.activity == k_skate_activity_grind_front50 )
+      wheels[0].state = k_collider_state_disabled;
+   if( s->state.activity == k_skate_activity_grind_5050 )
    {
-      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 );
-
-      rb_effect_spring_target_vector( &player->rb, refdir, plane_z,
-                                       k_manul_spring, k_manul_dampener,
-                                       s->substep_delta );
+      wheels[0].state = k_collider_state_disabled;
+      wheels[1].state = k_collider_state_disabled;
    }
 
-
-
-
-
-
-
+   /* all activities */
+   skate_apply_steering_model( player );
+   skate_adjust_up_direction( player );
+   skate_apply_cog_model( player );
+   skate_apply_jump_model( player );
+   skate_apply_grab_model( player );
+   skate_apply_trick_model( player );
 
 
 begin_collision:;
@@ -1751,9 +2286,6 @@ begin_collision:;
    m4x3_mulv( player->rb.to_world, s->state.head_position, head_wp0 );
    v3_copy( player->rb.co, start_co );
 
-   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;
@@ -1790,7 +2322,7 @@ begin_collision:;
       float t;
       v3f n;
 
-      float cast_radius = wheels[i].radius - k_penetration_slop * 1.2f;
+      float cast_radius = wheels[i].radius - k_penetration_slop * 2.0f;
       if( spherecast_world( current, future, cast_radius, &t, n ) != -1)
          max_time = vg_minf( max_time, t * s->substep );
    }
@@ -1833,8 +2365,8 @@ begin_collision:;
     * --------------------------------------------------------------------------
     */
    m4x3_mulv( player->rb.to_world, s->state.head_position, head_wp1 );
-   vg_line( head_wp0, head_wp1, VG__RED );
 
+#if 0
    float t;
    v3f n;
    if( (v3_dist2( head_wp0, head_wp1 ) > 0.001f) &&
@@ -1843,106 +2375,11 @@ begin_collision:;
       v3_lerp( start_co, player->rb.co, t, player->rb.co );
       rb_update_transform( &player->rb );
 
-#if 0
       player__dead_transition( player );
-#endif
       return;
    }
-
-   /* 
-    * Phase 2-1+0.5: Grind collision
-    * --------------------------------------------------------------------------
-    */
-
-   for( int i=0; i<1; i++ )
-   {
-
-      /* 
-       * Grind collision detection 
-       * ------------------------------------------------
-       */
-      v3f grind_co, grind_n, grind_dir;
-      if( skate_grind_scansq( player, player->rb.co, 
-                              grind_co, grind_dir, grind_n ) )
-      {
-#if 0
-         rb_ct *ct = &manifold[ manifold_len ++ ];
-
-         v3_copy( truck, ct->co );
-         v3_copy( grind_n, ct->n );
-         ct->p = vg_maxf( 0.0f, ct->co[1] - truck[1] );
-#endif
-
-         v3f target_dir;
-         v3_cross( grind_dir, (v3f){0.0f,1.0f,0.0f}, target_dir );
-         target_dir[1] = 0.0f;
-
-         if( v3_length2( target_dir ) <= 0.001f )
-            continue;
-
-         if( fabsf(v3_dot( player->rb.v, grind_dir )) < 0.7071f )
-            continue;
-
-         v3_copy( grind_co, player->rb.co );
-
-         q_axis_angle( player->rb.q, (v3f){0.0f,1.0f,0.0f}, 
-                       -atan2f( target_dir[2], target_dir[0] ) );
-
-         wheels[0].state = k_collider_state_disabled;
-         wheels[1].state = k_collider_state_disabled;
-         v3_muls( grind_dir, v3_dot(player->rb.v,grind_dir), player->rb.v );
-         v3_zero( player->rb.w );
-
-         rb_update_transform( &player->rb );
-
-
-#if 0
-         v3f displacement, dir;
-         v3_sub( truck, grind_co, displacement );
-         v3_copy( displacement, dir );
-         v3_normalize( dir );
-
-         v3f rv, raW;
-         q_mulv( player->rb.q, wheels[i].pos, 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, s->substep_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 );
-
-         rb_effect_spring_target_vector( &player->rb, player->rb.to_world[1], 
-                                          grind_n,
-                                          k_board_spring, k_board_dampener,
-                                          s->substep_delta );
-
-         v3f adj;
-         v3_cross( grind_dir, (v3f){0.0f,1.0f,0.0f}, adj );
-         rb_effect_spring_target_vector( &player->rb, player->rb.to_world[2],
-                                          adj,
-                                          k_grind_spring, k_grind_dampener,
-                                          s->substep_delta );
 #endif
 
-         s->state.activity = k_skate_activity_grind;
-      }
-      else
-         s->state.activity = k_skate_activity_ground;
-   }
-
-
    /*
     * Phase 1: Regular collision detection
     *          TODO: Me might want to automatically add contacts from CCD, 
@@ -1985,6 +2422,35 @@ begin_collision:;
       manifold_len += l;
    }
 
+   float grind_radius = k_board_radius * 0.75f;
+   rb_capsule capsule = { .height = (k_board_length+0.2f)*2.0f, 
+                          .radius=grind_radius };
+   m4x3f mtx;
+   v3_muls( player->rb.to_world[0],  1.0f, mtx[0] );
+   v3_muls( player->rb.to_world[2], -1.0f, mtx[1] );
+   v3_muls( player->rb.to_world[1],  1.0f, mtx[2] );
+   v3_muladds( player->rb.to_world[3], player->rb.to_world[1], 
+               grind_radius + k_board_radius*0.25f, mtx[3] );
+
+   rb_ct *cman = &manifold[manifold_len];
+
+   int l = rb_capsule__scene( mtx, &capsule, NULL, &world.rb_geo.inf.scene,
+                              cman );
+   manifold_len += l;
+
+   debug_capsule( mtx, capsule.radius, capsule.height, VG__WHITE );
+
+   /* add limits */
+   for( int i=0; i<s->limit_count; i++ )
+   {
+      struct grind_limit *limit = &s->limits[i];
+      rb_ct *ct = &manifold[ manifold_len ++ ];
+      m4x3_mulv( player->rb.to_world, limit->ra, ct->co );
+      m3x3_mulv( player->rb.to_world, limit->n, ct->n );
+      ct->p = limit->p;
+      ct->type = k_contact_type_default;
+   }
+
    /* 
     * Phase 3: Dynamics
     * --------------------------------------------------------------------------
@@ -2021,8 +2487,9 @@ begin_collision:;
    m3x3_mul( iI, player->rb.to_local, iIw );
    m3x3_mul( player->rb.to_world, iIw, iIw );
 
-   m4x3_mulv( player->rb.to_world, weight, world_cog );
-   vg_line_pt3( world_cog, 0.1f, VG__BLACK );
+   v3f world_cog;
+   m4x3_mulv( player->rb.to_world, s->weight_distribution, world_cog );
+   vg_line_pt3( world_cog, 0.02f, VG__BLACK );
 
    for( int j=0; j<10; j++ )
    {
@@ -2049,9 +2516,6 @@ begin_collision:;
                vn = v3_dot( rv, ct->n ),
                lambda = normal_mass * ( -vn );
 
-         /* FIXME! */
-         v3_muladds( player->rb.co, ct->n, ct->bias*0.02f, player->rb.co );
-
          float temp = ct->norm_impulse;
          ct->norm_impulse = vg_maxf( temp + lambda, 0.0f );
          lambda = ct->norm_impulse - temp;
@@ -2070,6 +2534,11 @@ begin_collision:;
       }
    }
 
+   v3f dt;
+   rb_depenetrate( manifold, manifold_len, dt );
+   v3_add( dt, player->rb.co, player->rb.co );
+   rb_update_transform( &player->rb );
+
    substep_count ++;
 
    if( s->substep >= 0.0001f )
@@ -2090,30 +2559,8 @@ begin_collision:;
                             wheels[i].colour }[ wheels[i].state ]);
    }
 
-#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 );
+   vg_line_pt3( s->state.cog, 0.02f,  VG__WHITE );
 
    teleport_gate *gate;
    if( (gate = world_intersect_gates( player->rb.co, s->state.prev_pos )) )
@@ -2151,11 +2598,21 @@ VG_STATIC void player__skate_im_gui( player_instance *player )
                                                 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] );
+   const char *activity_txt[] = 
+   {
+      "air",
+      "ground",
+      "undefined (INVALID)",
+      "grind_any (INVALID)",
+      "grind_boardslide",
+      "grind_noseslide",
+      "grind_tailslide",
+      "grind_back50",
+      "grind_front50",
+      "grind_5050"
+   };
+
+   player__debugtext( 1, "activity: %s", activity_txt[s->state.activity] );
 #if 0
    player__debugtext( 1, "steer_s: %5.2f %5.2f [%.2f %.2f]",
                         s->state.steerx_s, s->state.steery_s,
@@ -2230,8 +2687,7 @@ VG_STATIC void player__skate_animate( player_instance *player,
    
    /* movement information */
    {
-      int iair = (s->state.activity == k_skate_activity_air) ||
-                 (s->state.activity == k_skate_activity_grind );
+      int iair = s->state.activity == k_skate_activity_air;
 
       float dirz = s->state.reverse > 0.0f? 0.0f: 1.0f,
             dirx = s->state.slip < 0.0f?    0.0f: 1.0f,
@@ -2384,11 +2840,11 @@ VG_STATIC void player__skate_animate( player_instance *player,
          }
 
          v3f p1, p2;
-         m4x3_mulv( player->rb.to_world, up, p1 );
-         m4x3_mulv( player->rb.to_world, ndir, p2 );
+         m3x3_mulv( player->rb.to_world, up, p1 );
+         m3x3_mulv( player->rb.to_world, ndir, p2 );
 
-         vg_line( player->rb.co, p1, VG__PINK );
-         vg_line( player->rb.co, p2, VG__CYAN );
+         vg_line_arrow( player->rb.co, p1, 0.25f, VG__PINK );
+         vg_line_arrow( player->rb.co, p2, 0.25f, VG__PINK );
       }
 
 
@@ -2397,23 +2853,10 @@ VG_STATIC void player__skate_animate( player_instance *player,
                    *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 );
@@ -2423,26 +2866,12 @@ VG_STATIC void player__skate_animate( player_instance *player,
       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_mul( qyawr, 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;
diff --git a/player_skate.h b/player_skate.h
index 11c66e9..e3f639a 100644
--- a/player_skate.h
+++ b/player_skate.h
@@ -13,7 +13,14 @@ struct player_skate
       {
          k_skate_activity_air,
          k_skate_activity_ground,
-         k_skate_activity_grind
+         k_skate_activity_undefined,
+         k_skate_activity_grind_any,
+         k_skate_activity_grind_boardslide,
+         k_skate_activity_grind_noseslide,
+         k_skate_activity_grind_tailslide,
+         k_skate_activity_grind_back50,
+         k_skate_activity_grind_front50,
+         k_skate_activity_grind_5050
       }
       activity,
       activity_prev;
@@ -63,6 +70,36 @@ struct player_skate
    state,
    state_gate_storage;
 
+
+   /* animation */
+   struct skeleton_anim *anim_stand, *anim_highg, *anim_slide,
+                        *anim_air,
+                        *anim_push,  *anim_push_reverse,
+                        *anim_ollie, *anim_ollie_reverse,
+                        *anim_grabs, *anim_stop;
+   v3f 
+       board_trick_residualv,
+       board_trick_residuald;
+
+   float blend_slide,
+         blend_z,
+         blend_x,
+         blend_fly,
+         blend_stand,
+         blend_push,
+         blend_jump,
+         blend_airdir;
+
+   v2f wobble;
+
+   /*
+    * Physics 
+    * ----------------------------------------------------
+    */
+
+   float substep,
+         substep_delta;
+
    struct land_prediction
    {
       v3f   log[50];
@@ -87,33 +124,19 @@ struct player_skate
    float land_dist;
    v3f land_normal;
 
-   /* animation */
-   struct skeleton_anim *anim_stand, *anim_highg, *anim_slide,
-                        *anim_air,
-                        *anim_push,  *anim_push_reverse,
-                        *anim_ollie, *anim_ollie_reverse,
-                        *anim_grabs, *anim_stop;
-   v3f board_offset,
-       board_trick_residualv,
-       board_trick_residuald;
-   v4f board_rotation;
-
-   float blend_slide,
-         blend_z,
-         blend_x,
-         blend_fly,
-         blend_stand,
-         blend_push,
-         blend_jump,
-         blend_airdir;
-
-   float substep,
-         substep_delta;
+   v3f surface_picture,
+       weight_distribution,
+       grind_vec;
 
-   v2f wobble;
+   float grind_strength;
 
-   float debug_normal_pressure;
-   u32 device_id_walk;
+   struct grind_limit
+   {
+      v3f ra, n;
+      float p;
+   }
+   limits[3];
+   u32 limit_count;
 };
 
 VG_STATIC void player__skate_bind         ( player_instance *player );
diff --git a/player_walk.c b/player_walk.c
index d916c26..d5f4aa0 100644
--- a/player_walk.c
+++ b/player_walk.c
@@ -464,20 +464,7 @@ VG_STATIC void player__walk_update( player_instance *player )
     * Depenetrate
     */
    v3f dt;
-   v3_zero( dt );
-   for( int j=0; j<8; j++ )
-   {
-      for( int i=0; i<len; i++ )
-      {
-         struct contact *ct = &manifold[i];
-
-         float resolved_amt = v3_dot( ct->n, dt ),
-               remaining    = (ct->p-k_penetration_slop) - resolved_amt,
-               apply        = vg_maxf( remaining, 0.0f ) * 0.3f;
-
-         v3_muladds( dt, ct->n, apply, dt );
-      }
-   }
+   rb_depenetrate( manifold, len, dt );
    v3_add( dt, player->rb.co, player->rb.co );
 
    /* TODO: Stepping......
diff --git a/rigidbody.h b/rigidbody.h
index 5ca3e1e..746c684 100644
--- a/rigidbody.h
+++ b/rigidbody.h
@@ -214,13 +214,19 @@ VG_STATIC void rb_tangent_basis( v3f n, v3f tx, v3f ty )
 
 VG_STATIC void rb_debug_contact( rb_ct *ct )
 {
-   if( ct->type != k_contact_type_disabled )
+   v3f p1;
+   v3_muladds( ct->co, ct->n, 0.05f, p1 );
+
+   if( ct->type == k_contact_type_default )
    {
-      v3f p1;
-      v3_muladds( ct->co, ct->n, 0.05f, p1 );
       vg_line_pt3( ct->co, 0.0125f, 0xff0000ff );
       vg_line( ct->co, p1, 0xffffffff );
    }
+   else if( ct->type == k_contact_type_edge )
+   {
+      vg_line_pt3( ct->co, 0.0125f, 0xff00ffc0 );
+      vg_line( ct->co, p1, 0xffffffff );
+   }
 }
 
 VG_STATIC void debug_sphere( m4x3f m, float radius, u32 colour )
@@ -2004,6 +2010,26 @@ VG_STATIC void rb_prepare_contact( rb_ct *ct, float timestep )
    ct->tangent_impulse[1] = 0.0f;
 }
 
+/* calculate total move. manifold should belong to ONE object only */
+VG_STATIC void rb_depenetrate( rb_ct *manifold, int len, v3f dt )
+{
+   v3_zero( dt );
+
+   for( int j=0; j<7; j++ )
+   {
+      for( int i=0; i<len; i++ )
+      {
+         struct contact *ct = &manifold[i];
+
+         float resolved_amt = v3_dot( ct->n, dt ),
+               remaining    = (ct->p-k_penetration_slop) - resolved_amt,
+               apply        = vg_maxf( remaining, 0.0f ) * 0.4f;
+
+         v3_muladds( dt, ct->n, apply, dt );
+      }
+   }
+}
+
 /*
  * Initializing things like tangent vectors
  */