From 6069ed841523d832ac004061d29bc3768bb2c211 Mon Sep 17 00:00:00 2001
From: Doyle Thai <dyl.thai@gmail.com>
Date: Thu, 24 Nov 2016 00:27:24 +1100
Subject: [PATCH] Fix interval overlap case for collision detection

If one interval were completely contained within another then the logic would
not correctly identify the overlap. Instead check the length of the intervals
and ensure the smaller interval of the two is compared against the larger one.
---
 src/Asteroid.c             | 69 +++++++++++++++++++++-----------------
 src/include/Dengine/Math.h | 13 ++++++-
 2 files changed, 51 insertions(+), 31 deletions(-)

diff --git a/src/Asteroid.c b/src/Asteroid.c
index 614f31d..d22a54b 100644
--- a/src/Asteroid.c
+++ b/src/Asteroid.c
@@ -389,6 +389,34 @@ b32 moveEntity(GameState *state, Entity *entity, i32 entityIndex, v2 ddP,
 	return willCollide;
 }
 
+INTERNAL void addAsteroid(GameState *state, v2 windowSize)
+{
+	Entity *asteroid = &state->entityList[state->entityIndex];
+	asteroid->id     = state->entityIndex++;
+
+	i32 randValue = rand();
+	i32 randX     = (randValue % (i32)windowSize.w);
+	i32 randY     = (randValue % (i32)windowSize.h);
+	asteroid->pos = V2i(randX, randY);
+
+	asteroid->size       = V2(75.0f, 75.0f);
+	asteroid->hitbox     = asteroid->size;
+	asteroid->offset     = V2(asteroid->size.w * -0.5f, 0);
+	asteroid->scale      = 1;
+	asteroid->rotation   = 45;
+	asteroid->type       = entitytype_asteroid;
+	asteroid->direction  = direction_null;
+	asteroid->renderMode = rendermode_polygon;
+
+	asteroid->numVertexPoints = 10;
+	asteroid->vertexPoints    = createAsteroidVertexList(
+	    &state->persistentArena, asteroid->numVertexPoints,
+	    (i32)(asteroid->size.x * 0.5f));
+
+	asteroid->tex      = NULL;
+	asteroid->collides = TRUE;
+}
+
 void asteroid_gameUpdateAndRender(GameState *state, Memory *memory,
                                   v2 windowSize, f32 dt)
 {
@@ -406,34 +434,9 @@ void asteroid_gameUpdateAndRender(GameState *state, Memory *memory,
 		state->pixelsPerMeter = 70.0f;
 
 		{ // Init asteroid entities
-			i32 numAsteroids = 1;
+			i32 numAsteroids = 15;
 			for (i32 i = 0; i < numAsteroids; i++)
-			{
-				Entity *asteroid = &state->entityList[state->entityIndex];
-				asteroid->id     = state->entityIndex++;
-
-				i32 randValue = rand();
-				i32 randX     = (randValue % (i32)windowSize.w);
-				i32 randY     = (randValue % (i32)windowSize.h);
-				asteroid->pos = V2i(100 + (i * 100), 500);
-
-				asteroid->size       = V2(100.0f, 100.0f);
-				asteroid->hitbox     = asteroid->size;
-				asteroid->offset     = V2(asteroid->size.w * -0.5f, 0);
-				asteroid->scale      = 1;
-				asteroid->rotation   = 45;
-				asteroid->type       = entitytype_asteroid;
-				asteroid->direction  = direction_null;
-				asteroid->renderMode = rendermode_polygon;
-
-				asteroid->numVertexPoints = i + 10;
-				asteroid->vertexPoints    = createAsteroidVertexList(
-						&state->persistentArena, asteroid->numVertexPoints,
-						(i32)(asteroid->size.x * 0.5f));
-
-				asteroid->tex      = NULL;
-				asteroid->collides = TRUE;
-			}
+				addAsteroid(state, windowSize);
 		}
 
 #if 1
@@ -503,6 +506,12 @@ void asteroid_gameUpdateAndRender(GameState *state, Memory *memory,
 		}
 	}
 
+	if (getKeyStatus(&state->input.keys[keycode_left_square_bracket],
+	                 readkeytype_repeat, 0.2f, dt))
+	{
+		addAsteroid(state, windowSize);
+	}
+
 	for (i32 i = 0; i < state->entityIndex; i++)
 	{
 		Entity *entity = &state->entityList[i];
@@ -574,7 +583,7 @@ void asteroid_gameUpdateAndRender(GameState *state, Memory *memory,
 			}
 
 			v2 ddP = {0};
-#if 0
+#if 1
 			switch (entity->direction)
 			{
 			case direction_north:
@@ -642,8 +651,8 @@ void asteroid_gameUpdateAndRender(GameState *state, Memory *memory,
 			// NOTE(doyle): Make asteroids start and move at constant speed
 			ddPSpeedInMs = 1;
 			entity->dP   = v2_scale(ddP, state->pixelsPerMeter * ddPSpeedInMs);
-#endif
 			entity->rotation += (60 * dt);
+#endif
 		}
 
 		b32 willCollide = moveEntity(state, entity, i, ddP, dt, ddPSpeedInMs);
@@ -661,7 +670,7 @@ void asteroid_gameUpdateAndRender(GameState *state, Memory *memory,
 		                entityColor, flags);
 	}
 
-#if 0
+#if 1
 	debug_drawUi(state, dt);
 	debug_clearCounter();
 #endif
diff --git a/src/include/Dengine/Math.h b/src/include/Dengine/Math.h
index 877c822..48e195c 100644
--- a/src/include/Dengine/Math.h
+++ b/src/include/Dengine/Math.h
@@ -191,9 +191,20 @@ INTERNAL inline v2 v2_normalise(const v2 a)
 	return result;
 }
 
-INTERNAL inline b32 v2_intervalsOverlap(const v2 a, const v2 b) 
+INTERNAL inline b32 v2_intervalsOverlap(v2 a, v2 b)
 {
 	b32 result = FALSE;
+	
+	f32 lenOfA = a.max - a.min;
+	f32 lenOfB = b.max - b.min;
+
+	if (lenOfA > lenOfB)
+	{
+		v2 tmp = a;
+		a      = b;
+		b      = tmp;
+	}
+
 	if ((a.min >= b.min && a.min <= b.max) ||
 	    (a.max >= b.min && a.max <= b.max))
 	{