From: Joshua Grams <josh@qualdan.com>
Date: Sat, 25 Mar 2006 20:57:18 +0000 (+0000)
Subject: correct bounce math?
X-Git-Tag: 0.4~12
X-Git-Url: https://jasonwoof.com/gitweb/?p=vor.git;a=commitdiff_plain;h=d73d4327d339764fccf57c04cc2d975cfdef4b3c

correct bounce math?
---

diff --git a/sprite.c b/sprite.c
index abe9fb3..e63fd68 100644
--- a/sprite.c
+++ b/sprite.c
@@ -340,8 +340,8 @@ void
 bounce(Sprite *a, Sprite *b)
 {
 	float x, y, n;
-	float va, vb;
-	float ma, mb, mr;
+	float va, vb, vc;
+	float ma, mb;
 
 	// (x, y) is unit vector pointing from A's center to B's center.
 	x = (b->x + b->w / 2) - (a->x + a->w / 2);
@@ -352,10 +352,9 @@ bounce(Sprite *a, Sprite *b)
 	va = max(x*a->dx + y*a->dy, 0);
 	vb = min(x*b->dx + y*b->dy, 0);
 
-	// mass ratio
 	ma = sprite_mass(a); mb = sprite_mass(b);
-	if(ma && mb) mr = mb/ma; else mr = 1;
+	vc = (va*ma + vb*mb) / (ma+mb);
 
-	a->dx += x*(mb*vb - ma*va)/ma; a->dy += y*(mb*vb - ma*va)/ma;
-	b->dx += x*(ma*va - mb*vb)/mb; b->dy += y*(ma*va - mb*vb)/mb;
+	a->dx += 2*x*(vc-va); a->dy += 2*y*(vc-va);
+	b->dx += 2*x*(vc-vb); b->dy += 2*y*(vc-vb);
 }