From: Matthew Owens <matthew@owens.tech>
Date: Fri, 2 Oct 2020 13:00:06 +0000 (+0100)
Subject: added collision detection functions
X-Git-Url: https://git.owens.tech///git?a=commitdiff_plain;h=b037fd12068b677aa91af119a068a1f72315ec67;p=pong.git

added collision detection functions
---

diff --git a/src/main.c b/src/main.c
index e686468..e200376 100644
--- a/src/main.c
+++ b/src/main.c
@@ -90,6 +90,37 @@ static void vbox_render(const Vbox *b)
 	SDL_RenderFillRect(renderer, &b->r);
 }
 
+static bool ll_collision(float x1, float y1, float x2, float y2,
+	   float x3, float y3, float x4, float y4, Vec2df *intersect)
+{
+	float uA = ((x4-x3)*(y1-y3) - (y4-y3)*(x1-x3)) /
+			   ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+	float uB = ((x2-x1)*(y1-y3) - (y2-y1)*(x1-x3)) /
+			   ((y4-y3)*(x2-x1) - (x4-x3)*(y2-y1));
+
+	if(intersect) {
+		intersect->x = x1 + (uA * (x2-x1));
+		intersect->y = y1 + (uB * (y2-y1));
+	}
+
+	return (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1);
+}
+
+/*
+ * (v)box / line collision
+ * returns 0 on no collision, 1/2/3/4 on left/right/top/bottom
+ */
+static int lr_collision(Vec2df start, Vec2df end, SDL_Rect r, Vec2df *i) {
+	if(ll_collision(start.x, start.y, end.x, end.y, r.x, r.y, r.x, r.y + r.h, i))
+		return 1; //left
+	if(ll_collision(start.x, start.y, end.x, end.y, r.x + r.w, r.y, r.x + r.w, r.y + r.h, i))
+		return 2; //right
+	if(ll_collision(start.x, start.y, end.x, end.y, r.x, r.y, r.x + r.w, r.y , i))
+		return 3; //top
+	if(ll_collision(start.x, start.y, end.x, end.y, r.x, r.y + r.h, r.x + r.w, r.y + r.h, i))
+		return 4; //bottom
+}
+
 static void paddle_update(const Uint8* keyStates, float dt)
 {
 	pad.v.x = 0;
@@ -112,18 +143,32 @@ static void paddle_update(const Uint8* keyStates, float dt)
 static void ball_update(float dt)
 {
 	bool collisionResponded = false;
+	float halfw = ball.r.w / 2;
+	float halfh = ball.r.h / 2;
+
 	// applying velocity
 	ball.r.x += ball.v.x * dt;
 	ball.r.y += ball.v.y * dt;
 
-	vline[0].x = ball.r.x + ball.r.w / 2;
-	vline[0].y = ball.r.y + ball.r.h / 2;
-
-	// todo: fix
-	// terniary should be replaced with the size of the ball * normalised vel
-	vline[1].x = vline[0].x + ball.v.x + ( ball.v.x > 0 ? ball.r.w / 2 : 0);
-	vline[1].y = vline[0].y + ball.v.y + ( ball.v.y > 0 ? ball.r.h / 2 : 0);
-
+	// velocity projection start to center of ball
+	vline[0].x = ball.r.x + halfw;
+	vline[0].y = ball.r.y + halfh;
+
+	// setting velocity projection end
+	vline[1].x = vline[0].x + ball.v.x;
+	if(ball.v.x > 0) { vline[1].x += halfw; }
+	else if (ball.v.x < 0) {vline[1].x -= halfw; }
+	vline[1].y = vline[0].y + ball.v.y;
+	if(ball.v.y > 0) { vline[1].y += halfh; }
+	else if (ball.v.y < 0) {vline[1].y -= halfh; }
+
+	// are we going to collide with the paddle? 
+	{
+		int willCollide = lr_collision(vline[0], vline[1], pad.r, NULL);
+		switch(willCollide) {
+			//TODO: set ball loc to colliding wall, invert vel & skip vel add
+		}
+	}
 
 	// screen bounds checks & responses
 	if(ball.r.x + ball.r.w > windowSize.x && !collisionResponded){
@@ -223,7 +268,6 @@ static void cleanup()
 
 int main()
 {
-	//TODO: run on primary display
 	if(!init()) { return 1; }
 
 	while(!quit) {