+ v3f raw, wsp;
+ m3x3_mulv( localplayer.rb.to_world, ra, raw );
+ v3_add( localplayer.rb.co, raw, wsp );
+
+ if( skate_grind_scansq( wsp, localplayer.rb.v, 0.3, inf ) ){
+ if( fabsf(v3_dot( localplayer.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( localplayer.rb.v, inf->n,
+ -v3_dot( localplayer.rb.v, inf->n ), pv );
+
+ if( v3_length2( pv ) < 0.0001f )
+ return 0;
+ v3_normalize( pv );
+
+ if( fabsf(v3_dot( pv, inf->dir )) < k_grind_axel_max_angle )
+ return 0;
+
+ if( v3_dot( localplayer.rb.v, inf->n ) > 0.5f )
+ return 0;
+
+ v3f local_co, local_dir, local_n;
+ m4x3_mulv( localplayer.rb.to_local, inf->co, local_co );
+ m3x3_mulv( localplayer.rb.to_local, inf->dir, local_dir );
+ m3x3_mulv( localplayer.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( localplayer.rb.w, raw, rv );
+ v3_add( localplayer.rb.v, rv, rv );
+
+ if( (local_co[1] >= truck_height) &&
+ (v2_length2( delta ) <= k_board_radius*k_board_radius) )
+ {
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
+static void skate_boardslide_apply( struct grind_info *inf ){
+ struct player_skate_state *state = &player_skate.state;
+
+ v3f local_co, local_dir, local_n;
+ m4x3_mulv( localplayer.rb.to_local, inf->co, local_co );
+ m3x3_mulv( localplayer.rb.to_local, inf->dir, local_dir );
+ m3x3_mulv( localplayer.rb.to_local, inf->n, local_n );
+
+ v3f intersection;
+ v3_muladds( local_co, local_dir, local_co[0]/-local_dir[0],
+ intersection );
+ v3_copy( intersection, player_skate.weight_distribution );
+
+ skate_grind_decay( inf, 0.0125f );
+ skate_grind_friction( inf, 0.25f );
+
+ /* direction alignment */
+ v3f dir, perp;
+ v3_cross( local_dir, local_n, perp );
+ v3_muls( local_dir, vg_signf(local_dir[0]), dir );
+ v3_muls( perp, vg_signf(perp[2]), perp );
+
+ m3x3_mulv( localplayer.rb.to_world, dir, dir );
+ m3x3_mulv( localplayer.rb.to_world, perp, perp );
+
+ v4f qbalance;
+ q_axis_angle( qbalance, dir, local_co[0]*k_grind_balance );
+ q_mulv( qbalance, perp, perp );
+
+ rb_effect_spring_target_vector( &localplayer.rb, localplayer.rb.to_world[0],
+ dir,
+ k_grind_spring, k_grind_dampener,
+ k_rb_delta );
+
+ rb_effect_spring_target_vector( &localplayer.rb, localplayer.rb.to_world[2],
+ perp,
+ k_grind_spring, k_grind_dampener,
+ k_rb_delta );
+
+ vg_line_arrow( localplayer.rb.co, dir, 0.5f, VG__GREEN );
+ vg_line_arrow( localplayer.rb.co, perp, 0.5f, VG__BLUE );
+
+ v3_copy( inf->dir, player_skate.grind_dir );
+}
+
+static int skate_boardslide_entry( struct grind_info *inf ){
+ struct player_skate_state *state = &player_skate.state;
+
+ if( skate_grind_scansq( localplayer.rb.co,
+ localplayer.rb.to_world[0], k_board_length,
+ inf ) )
+ {
+ v3f local_co, local_dir;
+ m4x3_mulv( localplayer.rb.to_local, inf->co, local_co );
+ m3x3_mulv( localplayer.rb.to_local, inf->dir, local_dir );
+
+ if( (fabsf(local_co[2]) <= k_board_length) && /* within wood area */
+ (local_co[1] >= 0.0f) && /* at deck level */
+ (fabsf(local_dir[0]) >= 0.25f) ) /* perpendicular to us */
+ {
+ if( fabsf(v3_dot( localplayer.rb.v, inf->dir )) < k_grind_axel_min_vel )
+ return 0;
+
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
+static int skate_boardslide_renew( struct grind_info *inf ){
+ struct player_skate_state *state = &player_skate.state;
+
+ if( !skate_grind_scansq( localplayer.rb.co,
+ localplayer.rb.to_world[0], k_board_length,
+ inf ) )
+ return 0;
+
+ /* Exit condition: cant see grind target directly */
+ v3f vis;
+ v3_muladds( localplayer.rb.co, localplayer.rb.to_world[1], 0.2f, vis );
+ if( !skate_point_visible( vis, inf->co ) )
+ return 0;
+
+ /* Exit condition: minimum velocity not reached, but allow a bit of error */
+ float dv = fabsf(v3_dot( localplayer.rb.v, inf->dir )),
+ minv = k_grind_axel_min_vel*0.8f;