add elastic collisions, accurate friction

draw.c

@@ -256,7 +256,7 @@ int distance_colour(int x, int y, int x2, int y2, int blackpoint) {
 }
 
 void update_viewport(double x, double y) {
-    float xmargin = 0.26;
+    float xmargin = 0.5;
     float ymargin = 0.2;
 
     if (player.physics->position.x - viewport_pos.x > (1-xmargin) * width) {

game.c

@@ -196,13 +196,12 @@ player_st get_player(int x, int y) {
     player.physics->position.x = x;
     player.physics->position.y = y;
     player.physics->next_position = player.physics->position;
+    player.physics->obj_elasticity = 0.9;
+    player.physics->obj_friction = 0.3;
 
     // friction (not in use)
     player.physics->glob_friction = 40; // drag coef * area
 
-    // collisions
-    player.physics->obj_elasticity = 0.7;
-
     player.physics->collision_poly_size = 4 + 4;
     player.physics->collision_poly = calloc(player.physics->collision_poly_size, sizeof(Vect));
 
@@ -764,9 +763,17 @@ void advance_thing(Body * thing) {
     translation.x = translation.y = 0;
     int numcols = 0;
 
+    uint32_t now = SDL_GetTicks();
+    uint32_t time_delta = now - thing->last_advance_time ;
+    if (time_delta > 20) {
+        printf("ERROR too slow: %d\n", time_delta);
+        thing->last_advance_time = now;
+        time_delta = 20;
+    }
+    printf("TimeDELTA: %d\n", time_delta);
+
     // collisions
     if ((numcols = process_collisions(thing, &translation))) {
-        double mag = vect_mag(translation);
 
         /*double check = vect_scalar_projection(translation, thing->vel);*/
         /*if (check >= 0) {*/
@@ -774,42 +781,72 @@ void advance_thing(Body * thing) {
             /*translation.y *= -1;*/
         /*}*/
 
+        // correct position using translation vector.
         thing->next_position.x += translation.x;
         thing->next_position.y += translation.y;
 
+        // make unit vector
+        double mag = vect_mag(translation);
         translation.x = translation.x / mag;
         translation.y = translation.y / mag;
 
+        // get velocity in direction of collision
         mag = vect_scalar_projection(thing->vel, translation);
 
         Vect revert_vel;
 
         revert_vel.x = cos(vect_dir(translation)) * mag;
         revert_vel.y = sin(vect_dir(translation)) * mag;
+
         thing->vel.x -= revert_vel.x; 
         thing->vel.y -= revert_vel.y;
-
-        // accel
-        double norm = 9.81 * thing->obj_mass;
-        double fric_const = 0.52;
-        Vect x;
-        x.y = 0; x.x = 1;
-        if (vect_scalar_projection(thing->vel, translation) > 0) {
-            friction.x = translation.y;
-            friction.y = -translation.x;
+        
+        // add elasticity
+        thing->vel.x -= revert_vel.x * sqrt(thing->obj_elasticity); 
+        thing->vel.y -= revert_vel.y * sqrt(thing->obj_elasticity);
+
+        // add friction
+
+        Vect friction = vect_rotate(revert_vel, M_PI / 2);
+        double dir = vect_scalar_projection(thing->vel, friction);
+        if (dir > 0) {
+            friction = vect_rotate(friction, M_PI);
+        } 
+        double normal = vect_mag(revert_vel);
+        printf("norm: %f\n", normal);
+
+        if (fabs(thing->vel.x) <= fabs(friction.x)) {
+            thing->vel.x = 0;
+        } else {
+            thing->vel.x += thing->obj_friction * friction.x; 
+        }
+        if (fabs(thing->vel.y) <= fabs(friction.y)) {
+            thing->vel.y = 0;
         } else {
-            friction.x = -translation.y;
-            friction.y = translation.x;
+            thing->vel.y += thing->obj_friction * friction.y; 
         }
 
+        printf("velocity: %f %f\n", thing->vel.x, thing->vel.y);
+
+        /*double norm = 9.81 * thing->obj_mass;*/
+        /*Vect x;*/
+        /*x.y = 0; x.x = 1;*/
+        /*if (vect_scalar_projection(thing->vel, translation) > 0) {*/
+            /*friction.x = translation.y;*/
+            /*friction.y = -translation.x;*/
+        /*} else {*/
+            /*friction.x = -translation.y;*/
+            /*friction.y = translation.x;*/
+        /*}*/
+
         // force
-        friction.x = friction.x * norm * fric_const;
-        friction.y = friction.y * norm * fric_const;
+        /*friction.x = friction.x * norm * fric_const;*/
+        /*friction.y = friction.y * norm * fric_const;*/
      //   printf("friction accel: %e %e\n", friction.x, friction.y);
      //   printf("velocity: %e %e\n", thing->vel.x, thing->vel.y);
 
-        set_motor_newtons(thing, M_FRICTION, friction.x, friction.y);
-        set_motor_max_velocity(thing, M_FRICTION, vect_mag(project_vect(thing->vel, friction)));
+        /*set_motor_newtons(thing, M_FRICTION, friction.x, friction.y);*/
+        /*set_motor_max_velocity(thing, M_FRICTION, vect_mag(project_vect(thing->vel, friction)));*/
 
         // restitution force
         /*rest.x = 0;*/
@@ -855,14 +892,6 @@ void advance_thing(Body * thing) {
         }
     }
 
-    uint32_t now = SDL_GetTicks();
-
-    uint32_t time_delta = now - thing->last_advance_time ;
-    if (time_delta > 18) {
-        thing->last_advance_time = now;
-        time_delta = 18;
-    }
-    printf("TimeDELTA: %d\n", time_delta);
     
     // motors
     for (int i = 0; i < thing->num_motors; i++) {
@@ -1078,10 +1107,9 @@ void startgame(SDL_Renderer * ren) {
 
     world = create_world();
 
-
     SDL_GetRendererOutputSize(ren, &width, &height);
 
-    player = get_player(200,300);
+    player = get_player(200,1300);
 
     world_thing player_world;
 

game.h

@@ -92,6 +92,8 @@ typedef struct BodyStruct{
     // properties
     double obj_mass; // kgs
     double obj_elasticity; // rho
+    double obj_friction; // between 0 and 1 (fraction of lateral velocity 
+                         // that is removed)
 
     //float x_vel;
     //float y_vel;
@@ -100,9 +102,6 @@ typedef struct BodyStruct{
     //float y_acc;
     /*------------------*/
 
-    // constants
-    double elasticity;
-
     // collisions
     Vect *collision_poly;
     Vect *collision_shape;

main.c

@@ -93,7 +93,7 @@ int game(void) {
     
     SDL_Thread *physics_thread;
     int ignore;
-    physics_thread = SDL_CreateThread(physics_loop, "Physics", (void *)NULL);
+//    physics_thread = SDL_CreateThread(physics_loop, "Physics", (void *)NULL);
 
     bool once = true;
     startgame(ren);
@@ -114,6 +114,7 @@ int game(void) {
         }
         /* Redraw Screen */
         redraw(ren);
+        step(10);
     }
 
 }