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);
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);
}