rewording bounce calculations.

diff --git a/sprite.c b/sprite.c
index ec9fb01..0a6ab87 100644 (file)
--- a/sprite.c
+++ b/sprite.c
@@ -299,7 +299,7 @@ void
 bounce(Sprite *a, Sprite *b)
 {
        float x, y, n;
 bounce(Sprite *a, Sprite *b)
 {
        float x, y, n;

-       float da, db;
+       float va, vb;

        float ma, mb, mr;
 
        // (x, y) is unit vector pointing from A's center to B's center.
        float ma, mb, mr;
 
        // (x, y) is unit vector pointing from A's center to B's center.

@@ -308,13 +308,13 @@ bounce(Sprite *a, Sprite *b)
        n = sqrt(x*x + y*y); x /= n; y /= n;
 
        // velocities along (x, y), or 0 if already moving away.
        n = sqrt(x*x + y*y); x /= n; y /= n;
 
        // velocities along (x, y), or 0 if already moving away.

-       da = max(x*a->dx + y*a->dy, 0);
-       db = min(x*b->dx + y*b->dy, 0);
+       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;
 
 
        // mass ratio
        ma = sprite_mass(a); mb = sprite_mass(b);
        if(ma && mb) mr = mb/ma; else mr = 1;
 

-       a->dx += x*(db*mr - da); a->dy += y*(db*mr - da);
-       b->dx += x*(da/mr - db); b->dy += y*(da/mr - db);
+       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;

 }
 }