start on scuffed gjk collision detection

src/common.h

@@ -595,7 +595,10 @@ struct clip_rect {
 #define QUAD_UNIT_SQUARE (struct quad) { V2(0, 0), V2(0, 1), V2(1, 1), V2(1, 0) }
 #define QUAD_UNIT_SQUARE_CENTERED (struct quad) { V2(-0.5f, -0.5f), V2(0.5f, -0.5f), V2(0.5f, 0.5f), V2(-0.5f, 0.5f) }
 struct quad {
-    struct v2 p1, p2, p3, p4;
+    union {
+        struct { struct v2 p1, p2, p3, p4; };
+        struct { struct v2 e[4]; };
+    };
 };
 
 /* (T)ranslation, (R)otation, (S)cale */

src/draw.c

@@ -246,7 +246,7 @@ void draw_solid_arrow_line(struct renderer_canvas *canvas, struct v2 start, stru
 
     struct v2 head_start = v2_add(end, head_start_dir);
 
-    struct v2 head_p1_dir = v2_mul(v2_perp(head_start_dir), head_width_ratio);
+    struct v2 head_p1_dir = v2_mul(v2_perp_cw(head_start_dir), head_width_ratio);
     struct v2 head_p2_dir = v2_neg(head_p1_dir);
 
     struct v2 head_p1 = v2_add(head_start, head_p1_dir);

src/entity.h

@@ -73,6 +73,27 @@ struct entity {
     struct entity_handle first;
     struct entity_handle last;
 
+
+
+
+
+
+
+
+    /* TODO: Remove this (testing) */
+    b32 colliding;
+
+
+
+
+
+
+
+
+
+
+
+
     /* ====================================================================== */
     /* Activation */
 

src/game.c

@@ -177,6 +177,10 @@ INTERNAL void spawn_test_entities(void)
 
         e->sprite = sprite_tag_from_path(STR("res/graphics/box.ase"));
 
+        entity_enable_prop(e, ENTITY_PROP_PHYSICAL);
+        e->mass_unscaled = 70;
+        e->ground_friction = 1000;
+
         entity_set_xform(e, XFORM_TRS(.t = pos, .s = size, .r = rot));
     }
 
@@ -195,6 +199,117 @@ INTERNAL void spawn_test_entities(void)
     }
 }
 
+/* ========================== *
+ * Collision test
+ * ========================== */
+
+INTERNAL struct v2 quad_furthest_point(struct quad quad, struct v2 dir)
+{
+    struct v2 furthest = quad.e[0];
+    f32 furthest_dot = v2_dot(dir, furthest);
+    for (u32 i = 1; i < ARRAY_COUNT(quad.e); ++i) {
+        struct v2 p = quad.e[i];
+        f32 dot = v2_dot(dir, p);
+        if (dot > furthest_dot) {
+            furthest = p;
+            furthest_dot = dot;
+        }
+    }
+    return furthest;
+}
+
+INTERNAL struct v2 quad_support_point(struct quad q0, struct quad q1, struct v2 dir)
+{
+    return v2_sub(quad_furthest_point(q0, dir), quad_furthest_point(q1, v2_neg(dir)));
+}
+
+#if 0
+INTERNAL struct v2 normal_towards_origin(struct v2 p0, struct v2 p1)
+{
+    struct v2 dir = v2_norm(v2_perp_cw(v2_sub(p1, p0)));
+#if 1
+    if (v2_dot(dir, p0) > 0) {
+        dir = v2_neg(dir);
+    }
+#else
+    dir = v2_mul(dir, 1 - ((v2_dot(dir, p0) > 0) << 1));
+#endif
+    return dir;
+}
+#else
+INTERNAL struct v2 normal_towards_point(struct v2 start, struct v2 end, struct v2 p)
+{
+    struct v2 dir = v2_norm(v2_perp_cw(v2_sub(end, start)));
+#if 1
+    if (v2_dot(dir, v2_sub(p, start)) < 0) {
+        dir = v2_neg(dir);
+    }
+#else
+    dir = v2_mul(dir, 1 - ((v2_dot(dir, v2_sub(p, start)) > 0) << 1));
+#endif
+    return dir;
+}
+#endif
+
+INTERNAL b32 quad_collision_test(struct quad q0, struct quad q1)
+{
+    struct v2 q0_center = v2_div(v2_add(q0.p4, v2_add(q0.p3, v2_add(q0.p2, q0.p1))), 4);
+    struct v2 q1_center = v2_div(v2_add(q1.p4, v2_add(q1.p3, v2_add(q1.p2, q1.p1))), 4);
+
+    /* Simplex */
+    struct v2 s[3] = { 0 };
+    u32 s_len = 0;
+
+    /* Append first point to simplex */
+    struct v2 dir = v2_norm(v2_sub(q1_center, q0_center));
+    s[0] = quad_support_point(q0, q1, dir);
+    s_len = 1;
+
+    dir = v2_norm(v2_neg(s[0]));  /* Next point is towards origin */
+    while (true) {
+        /* Determine support point */
+        struct v2 p = quad_support_point(q0, q1, dir);
+        if (v2_dot(dir, p) < 0) {
+            /* Point did not cross origin */
+            return false;
+        }
+
+        if (s_len == 1) {
+            s[1] = p;
+            ++s_len;
+        } else if (s_len == 2) {
+            /* Line case */
+            /* Next dir is line normal towards origin */
+            s[2] = p;
+            ++s_len;
+            dir = normal_towards_point(s[0], s[1], V2(0, 0));
+        } else {
+            s[0] = s[1];
+            s[1] = s[2];
+            s[2] = p;
+
+            /* Triangle case */
+            struct v2 a = s[2];
+            struct v2 b = s[1];
+            struct v2 c = s[0];
+
+            dir = v2_neg(normal_towards_point(a, b, c));  /* Normal dir of ab pointing away from c */
+            if (v2_dot(dir, v2_neg(a)) >= 0) {
+                /* Point is in region ab, remove c from simplex */
+            } else {
+                dir = v2_neg(normal_towards_point(a, c, b));  /* Normal dir of ac pointing away from b */
+                if (v2_dot(dir, v2_neg(a)) >= 0) {
+                    /* Point is in region ac, remove b from simplex */
+                    s[1] = s[0];
+                } else {
+                    /* Point must be in simplex */
+                    return true;
+                }
+            }
+        }
+    }
+}
+
 /* ========================== *
  * Update
  * ========================== */
@@ -576,7 +691,7 @@ INTERNAL void game_update(struct game_cmd_array game_cmds)
                     activate_now(force);
                 } else {
                     /* If velocity is below clamp_epsilon, stop entity movement. */
-                    f32 mass = ent->mass_unscaled * xform_get_determinant(xf);
+                    f32 mass = ent->mass_unscaled * math_fabs(xform_get_determinant(xf));
                     struct entity *impulse = entity_alloc(ent);
                     entity_enable_prop(impulse, ENTITY_PROP_IMPULSE);
                     impulse->force = v2_mul(v2_neg(velocity), mass);
@@ -587,16 +702,16 @@ INTERNAL void game_update(struct game_cmd_array game_cmds)
     }
 
     /* ========================== *
-     * Simulate physics
+     * Integrate forces & impulses
      * ========================== */
 
-    /* TODO: Run physics on top-level entities, and then calculate child xforms as part of physics step (rather than caching at each xform_get). */
     for (u64 entity_index = 0; entity_index < store->reserved; ++entity_index) {
         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)) {
+        if (!entity_has_prop(ent, ENTITY_PROP_PHYSICAL)) continue;
+
         struct xform xf = entity_get_xform(ent);
-            f32 mass = ent->mass_unscaled * xform_get_determinant(xf);
+        f32 mass = ent->mass_unscaled * math_fabs(xform_get_determinant(xf));
 
         /* Determine acceleration from forces and impulses */
         struct v2 acceleration = V2(0, 0);
@@ -617,6 +732,46 @@ INTERNAL void game_update(struct game_cmd_array game_cmds)
         xf.og = v2_add(xf.og, v2_add(tick_velocity, v2_mul(acceleration, dt)));
         entity_set_xform(ent, xf);
     }
+
+    /* ========================== *
+     * Collision
+     * ========================== */
+
+    for (u64 e0_index = 0; e0_index < store->reserved; ++e0_index) {
+        struct entity *e0 = &store->entities[e0_index];
+        if (!(e0->valid && entity_has_prop(e0, ENTITY_PROP_ACTIVE))) continue;
+        if (!entity_has_prop(e0, ENTITY_PROP_PHYSICAL)) continue;
+
+        struct xform e0_xf = entity_get_xform(e0);
+        struct quad e0_quad;
+        {
+            struct sprite_sheet *sheet = sprite_sheet_from_tag_await(sprite_frame_scope, e0->sprite);
+            struct sprite_sheet_slice slice = sprite_sheet_get_slice(sheet, STR("shape"), e0->animation_frame);
+            e0_quad = xform_mul_quad(e0_xf, quad_from_rect(slice.rect));
+        }
+
+        b32 colliding = false;
+        for (u64 e1_index = 0; e1_index < store->reserved; ++e1_index) {
+            struct entity *e1 = &store->entities[e1_index];
+            if (e1 == e0) continue;
+            if (!(e1->valid && entity_has_prop(e1, ENTITY_PROP_ACTIVE))) continue;
+            if (!entity_has_prop(e1, ENTITY_PROP_PHYSICAL)) continue;
+
+            struct xform e1_xf = entity_get_xform(e1);
+            struct quad e1_quad;
+            {
+                struct sprite_sheet *sheet = sprite_sheet_from_tag_await(sprite_frame_scope, e1->sprite);
+                struct sprite_sheet_slice slice = sprite_sheet_get_slice(sheet, STR("shape"), e1->animation_frame);
+                e1_quad = xform_mul_quad(e1_xf, quad_from_rect(slice.rect));
+            }
+
+            if (quad_collision_test(e0_quad, e1_quad)) {
+                colliding = true;
+                break;
+            }
+        }
+
+        e0->colliding = colliding;
     }
 
     /* ========================== *

src/math.h

@@ -543,11 +543,18 @@ INLINE f32 v2_len_squared(struct v2 a)
     return a.x * a.x + a.y * a.y;
 }
 
-INLINE struct v2 v2_perp(struct v2 a)
+/* Clockwise perpendicular vector */
+INLINE struct v2 v2_perp_cw(struct v2 a)
 {
     return V2(-a.y, a.x);
 }
 
+/* Counterclockwise perpendicular vector */
+INLINE struct v2 v2_perp_ccw(struct v2 a)
+{
+    return V2(a.y, -a.x);
+}
+
 INLINE struct v2 v2_norm(struct v2 a)
 {
     f32 l = v2_len_squared(a);
@@ -1008,9 +1015,8 @@ INLINE struct quad quad_from_line(struct v2 start, struct v2 end, f32 thickness)
 {
     f32 width = thickness / 2.f;
 
-    struct v2 rel = v2_sub(end, start);
+    struct v2 dir = v2_norm(v2_sub(end, start));
-    struct v2 dir = v2_norm(rel);
+    struct v2 dir_perp = v2_perp_cw(dir);
-    struct v2 dir_perp = v2_perp(dir);
 
     struct v2 left = v2_mul(dir_perp, -width);
     struct v2 right = v2_mul(dir_perp, width);

src/user.c

@@ -912,6 +912,14 @@ INTERNAL void user_update(void)
             if (!sprite_tag_is_nil(ent->sprite)) {
                 struct sprite_sheet *sheet = sprite_sheet_from_tag_async(sprite_frame_scope, sprite);
 
+                u32 quad_color = RGBA_32_F(1, 0, 0.5, 1);
+                u32 point_color = RGBA_32_F(1, 0, 0, 1);
+                u32 ray_color = RGBA_32_F(1, 0, 0.5, 1);
+
+                if (ent->colliding) {
+                    quad_color = RGBA_32_F(1, 1, 1, 1);
+                }
+
                 for (u64 i = 0; i < sheet->slice_groups_count; ++i) {
                     struct sprite_sheet_slice_group *group = &sheet->slice_groups[i];
                     if (string_ends_with(group->name, STR(".ray"))) continue;
@@ -926,16 +934,16 @@ INTERNAL void user_update(void)
                             struct quad quad = quad_from_rect(slice.rect);
                             quad = xform_mul_quad(sprite_xform, quad);
                             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));
+                            draw_solid_quad_line(G.viewport_canvas, quad, 2, quad_color);
                         }
 
-                        draw_solid_circle(G.viewport_canvas, center, 3, RGBA_32_F(1, 0, 0, 1), 20);
+                        draw_solid_circle(G.viewport_canvas, center, 3, point_color, 20);
 
                         if (slice.has_ray) {
                             struct v2 ray = xform_basis_mul_v2(sprite_xform, slice.dir);
                             ray = xform_basis_mul_v2(G.world_view, ray);
                             ray = v2_mul(v2_norm(ray), 25);
-                            draw_solid_arrow_ray(G.viewport_canvas, center, ray, 2, 10, RGBA_32_F(1, 0, 0.5, 1));
+                            draw_solid_arrow_ray(G.viewport_canvas, center, ray, 2, 10, ray_color);
                         }
                     }
                 }