From 44497dc461bc10bc2c4398e5311d4136007b3488 Mon Sep 17 00:00:00 2001
From: Joshua Grams <josh@qualdan.com>
Date: Thu, 23 Mar 2006 14:36:15 +0000
Subject: [PATCH] bouncy ship :)

---
 main.c   |    5 ++++-
 sprite.c |   50 ++++++++++++++++++++++++++++++++++----------------
 sprite.h |    4 +++-
 3 files changed, 41 insertions(+), 18 deletions(-)

diff --git a/main.c b/main.c
index 097969c..b075f0d 100644
--- a/main.c
+++ b/main.c
@@ -510,7 +510,10 @@ draw() {
 	}
 
 	if(state == GAMEPLAY) {
-		bang = collides(SPRITE(&ship));
+		Sprite *r = collides(SPRITE(&ship));
+		if(r) {
+			bounce(r, SPRITE(&ship));
+		}
 	}
 
 	ms_frame = SDL_GetTicks() - ms_end;
diff --git a/sprite.c b/sprite.c
index 38dae30..45cd0f9 100644
--- a/sprite.c
+++ b/sprite.c
@@ -1,3 +1,4 @@
+#include <math.h>
 #include <stdlib.h>
 #include <string.h>
 #include "config.h"
@@ -210,20 +211,20 @@ collide(Sprite *a, Sprite *b)
 	else return mask_collide(xov, yov, a, b);
 }
 
-int
+Sprite *
 hit_in_square(Sprite *r, Sprite *s)
 {
-	for(; r; r=r->next) {
-		if(collide(r, s)) return true;
-	}
-	return false;
+	for(; r; r=r->next)
+		if(collide(r, s)) break;
+	return r;
 }
 
-int
+Sprite *
 collides(Sprite *s)
 {
 	int l, r, t, b;
 	Sprite **sq;
+	Sprite *c;
 
 	l = (s->x + grid_size) / grid_size;
 	r = (s->x + s->w + grid_size) / grid_size;
@@ -231,21 +232,21 @@ collides(Sprite *s)
 	b = (s->y + s->h + grid_size) / grid_size;
 	sq = &sprites[set][l + t*gw];
 
-	if(hit_in_square(*sq, s)) return true;
-	if(l > 0 && hit_in_square(*(sq-1), s)) return true;
-	if(t > 0 && hit_in_square(*(sq-gw), s)) return true;
-	if(l > 0 && t > 0 && hit_in_square(*(sq-1-gw), s)) return true;
+	if((c = hit_in_square(*sq, s))) return c;
+	if(l > 0 && (c = hit_in_square(*(sq-1), s))) return c;
+	if(t > 0 && (c = hit_in_square(*(sq-gw), s))) return c;
+	if(l > 0 && t > 0 && (c = hit_in_square(*(sq-1-gw), s))) return c;
 
 	if(r > l) {
-		if(hit_in_square(*(sq+1), s)) return true;
-		if(t > 0 && hit_in_square(*(sq+1-gw), s)) return true;
+		if((c = hit_in_square(*(sq+1), s))) return c;
+		if(t > 0 && hit_in_square(*(sq+1-gw), s)) return c;
 	}
 	if(b > t) {
-		if(hit_in_square(*(sq+gw), s)) return true;
-		if(l > 0 && hit_in_square(*(sq-1+gw), s)) return true;
+		if((c = hit_in_square(*(sq+gw), s))) return c;
+		if(l > 0 && (c = hit_in_square(*(sq-1+gw), s))) return c;
 	}
-	if(r > l && b > t && hit_in_square(*(sq+1+gw), s)) return true;
-	return false;
+	if(r > l && b > t && (c = hit_in_square(*(sq+1+gw), s))) return c;
+	return NULL;
 }
 
 int
@@ -283,3 +284,20 @@ pixel_collides(float x, float y)
 	if(l > 0 && t > 0 && pixel_hit_in_square(*(sq-1-gw), x, y)) return true;
 	return false;
 }
+
+void
+bounce(Sprite *a, Sprite *b)
+{
+	float x, y, n;
+	float na, nb;
+
+	x = (b->x + b->w / 2) - (a->x + a->w / 2);
+	y = (b->y + b->h / 2) - (a->y + a->h / 2);
+	n = sqrt(x*x + y*y); x /= n; y /= n;
+
+	na = (x*a->dx + y*a->dy); // sqrt(a->dx*a->dx + a->dy*a->dy);
+	nb = (x*b->dx + y*b->dy); // sqrt(b->dx*b->dx + b->dy*b->dy);
+
+	a->dx += x*(nb-na); a->dy += y*(nb-na);
+	b->dx += x*(na-nb); b->dy += y*(na-nb);
+}
diff --git a/sprite.h b/sprite.h
index 4c0cefd..953d303 100644
--- a/sprite.h
+++ b/sprite.h
@@ -31,10 +31,12 @@ void add_sprite(Sprite *s);
 void move_sprite(Sprite *s);
 void move_sprites(void);
 
-int collides(Sprite *s);
+Sprite *collides(Sprite *s);
 int pixel_collides(float x, float y);
 void load_sprite(Sprite *sprite, char *filename);
 
+void bounce(Sprite *a, Sprite *b);
+
 
 // extended sprites
 
-- 
1.7.10.4