store and calculate mass from unscaled mass instead of density

src/entity.c

@@ -17,7 +17,7 @@ READONLY struct entity _g_entity_nil = {
     .cached_global_xform = XFORM_IDENT_NOCAST,
     .cached_global_xform_dirty = false,
     .verlet_xform = XFORM_IDENT_NOCAST,
-    .density = 1,
+    .mass_unscaled = 1,
     .sprite_local_xform = XFORM_IDENT_NOCAST,
     .sprite_tint = COLOR_WHITE
 };
@@ -28,7 +28,7 @@ GLOBAL READONLY struct entity g_entity_default = {
     .cached_global_xform = XFORM_IDENT_NOCAST,
     .cached_global_xform_dirty = true,
     .verlet_xform = XFORM_IDENT_NOCAST,
-    .density = 1,
+    .mass_unscaled = 1,
     .sprite_local_xform = XFORM_IDENT_NOCAST,
     .sprite_tint = COLOR_WHITE
 };

src/entity.h

@@ -101,7 +101,7 @@ struct entity {
 
     /* ENTITY_PROP_PHYSICAL */
 
-    f32 density;
+    f32 mass_unscaled;  /* Mass of entity in kg before any transformations */
     f32 ground_friction;
 
     /* Xform of the entity from the previous frame (used to calculate velocity) */

src/game.c

@@ -124,14 +124,14 @@ INTERNAL void spawn_test_entities(void)
         e->sprite_span_name = STR("idle.two_handed");
 
         entity_enable_prop(e, ENTITY_PROP_PLAYER_CONTROLLED);
-        e->control_move_force = 50;
+        e->control_move_force = 4500;
         e->control.focus = V2(0, -1);
-        e->ground_friction = 12;
-        e->density = 1.0;
-
-        player_ent = e;
 
         entity_enable_prop(e, ENTITY_PROP_PHYSICAL);
+        e->mass_unscaled = 70;
+        e->ground_friction = 1000;
+
+        player_ent = e;
     }
 
     /* Weapon */
@@ -156,6 +156,18 @@ INTERNAL void spawn_test_entities(void)
         player_ent->equipped = e->handle;
     }
 
+    /* Box */
+    {
+        struct v2 pos = V2(1, -1);
+        struct v2 size = V2(1, 1);
+        f32 rot = 0;
+        struct entity *e = entity_alloc(root);
+
+        e->sprite = sprite_tag_from_path(STR("res/graphics/box.ase"));
+
+        entity_set_xform(e, XFORM_TRS(.t = pos, .s = size, .r = rot));
+    }
+
     /* Camera */
     {
         struct entity *e = entity_alloc(root);
@@ -512,7 +524,8 @@ INTERNAL void game_update(struct game_cmd_array game_cmds)
                 bullet->bullet_src = ent->handle;
                 bullet->bullet_src_pos = rel_pos;
                 bullet->bullet_src_dir = rel_dir;
-                bullet->bullet_impulse = 5;
+                bullet->bullet_impulse = 0.25;
+                bullet->mass_unscaled = 0.04;
 
                 entity_enable_prop(bullet, ENTITY_PROP_BULLET);
             }
@@ -581,8 +594,8 @@ INTERNAL void game_update(struct game_cmd_array game_cmds)
         struct entity *ent = &store->entities[entity_index];
         if (!(ent->valid && entity_has_prop(ent, ENTITY_PROP_ACTIVE))) continue;
         if (entity_has_prop(ent, ENTITY_PROP_PHYSICAL)) {
-            f32 density = ent->density;
+            struct xform xf = entity_get_xform(ent);
-            f32 mass = density;  /* TODO: Real mass calculation */
+            f32 mass = ent->mass_unscaled * xform_get_determinant(xf);
 
             struct v2 acceleration = V2(0, 0);
 
@@ -605,7 +618,6 @@ INTERNAL void game_update(struct game_cmd_array game_cmds)
             }
 
             /* Verlet integration */
-            struct xform xf = entity_get_xform(ent);
             struct v2 tick_velocity = v2_sub(xf.og, ent->verlet_xform.og);
             ent->verlet_xform = xf;
             xf.og = v2_add(xf.og, v2_add(tick_velocity, v2_mul(acceleration, dt)));

src/math.h

@@ -907,6 +907,16 @@ INLINE struct v2 xform_invert_mul_v2(struct xform xf, struct v2 v)
     return res;
 }
 
+INLINE struct quad xform_mul_quad(struct xform xf, struct quad quad)
+{
+    return (struct quad) {
+            xform_mul_v2(xf, quad.p1),
+            xform_mul_v2(xf, quad.p2),
+            xform_mul_v2(xf, quad.p3),
+            xform_mul_v2(xf, quad.p4)
+    };
+}
+
 INLINE f32 xform_get_determinant(struct xform xf)
 {
     return v2_wedge(xf.bx, xf.by);
@@ -1027,16 +1037,6 @@ INLINE struct quad quad_scale(struct quad q, f32 s)
     return q;
 }
 
-INLINE struct quad quad_mul_xform(struct quad quad, struct xform m)
-{
-    return (struct quad) {
-        xform_mul_v2(m, quad.p1),
-        xform_mul_v2(m, quad.p2),
-        xform_mul_v2(m, quad.p3),
-        xform_mul_v2(m, quad.p4)
-    };
-}
-
 INLINE struct quad quad_round(struct quad quad)
 {
     return (struct quad) {

src/user.c

@@ -367,7 +367,7 @@ INTERNAL void debug_draw_xform(struct xform xf)
     y_ray = v2_mul(y_ray, ray_scale);
 
     struct quad quad = quad_from_rect(RECT(0, 0, 1, -1));
-    quad = quad_mul_xform(quad_scale(quad, 0.075f), xf);
+    quad = xform_mul_quad(xf, quad_scale(quad, 0.075f));
 
     draw_solid_arrow_ray(G.viewport_canvas, pos, x_ray, thickness, arrowhead_len, color_x);
     draw_solid_arrow_ray(G.viewport_canvas, pos, y_ray, thickness, arrowhead_len, color_y);
@@ -842,7 +842,7 @@ INTERNAL void user_update(void)
             /* TODO: Fade in placeholder if texture isn't loaded */
             if (sheet->loaded) {
                 struct sprite_sheet_frame frame = sprite_sheet_get_frame(sheet, ent->animation_frame);
-                struct quad quad = quad_mul_xform(QUAD_UNIT_SQUARE_CENTERED, sprite_xform);
+                struct quad quad = xform_mul_quad(sprite_xform, QUAD_UNIT_SQUARE_CENTERED);
                 struct draw_sprite_params params = DRAW_SPRITE_PARAMS(.sprite = sprite, .tint = ent->sprite_tint, .clip = frame.clip);
                 draw_sprite_quad(G.world_canvas, params, quad);
             }
@@ -924,8 +924,8 @@ INTERNAL void user_update(void)
 
                         if (!slice.has_ray) {
                             struct quad quad = quad_from_rect(slice.rect);
-                            quad = quad_mul_xform(quad, sprite_xform);
+                            quad = xform_mul_quad(sprite_xform, quad);
-                            quad = quad_mul_xform(quad, G.world_view);
+                            quad = xform_mul_quad(G.world_view, quad);
                             draw_solid_quad_line(G.viewport_canvas, quad, 2, RGBA_32_F(1, 0, 0.5, 1));
                         }
 
@@ -959,8 +959,8 @@ INTERNAL void user_update(void)
 
 
                 struct xform quad_xf = xform_mul(xf, ent->camera_quad_xform);
-                struct quad quad = quad_mul_xform(QUAD_UNIT_SQUARE_CENTERED, quad_xf);
+                struct quad quad = xform_mul_quad(quad_xf, QUAD_UNIT_SQUARE_CENTERED);
-                quad = quad_mul_xform(quad, G.world_view);
+                quad = xform_mul_quad(G.world_view, quad);
 
                 draw_solid_quad_line(G.viewport_canvas, quad, thickness, color);
             }
@@ -979,7 +979,7 @@ INTERNAL void user_update(void)
 
         struct v2 size = V2(t->width, t->height);
         struct xform xf = XFORM_TRS(.t = crosshair_pos, .s = size);
-        struct quad quad = quad_mul_xform(QUAD_UNIT_SQUARE_CENTERED, xf);
+        struct quad quad = xform_mul_quad(xf, QUAD_UNIT_SQUARE_CENTERED);
         draw_sprite_quad(G.viewport_canvas, DRAW_SPRITE_PARAMS(.sprite = crosshair_tag, .tint = tint), quad);
 
         struct rect cursor_clip = RECT_FROM_V2(G.viewport_screen_offset, G.viewport_size);