correct bounce math?

[vor.git] / sprite.c

diff --git a/sprite.c b/sprite.c
index 809547b..e63fd68 100644 (file)
--- a/sprite.c
+++ b/sprite.c
@@ -302,36 +302,37 @@ pixel_collide(Sprite *s, int x, int y)
        return s->mask[(y*s->mask_w) + (x>>5)] & pmask;
 }
 
-int
+Sprite *
 pixel_hit_in_square(Sprite *r, float x, float y)
 {
        for(; r; r=r->next) {
-               if(COLLIDES(r) && pixel_collide(r, x, y)) return 1;
+               if(COLLIDES(r) && pixel_collide(r, x, y)) return r;
        }
        return 0;
 }
 
-int
+Sprite *
 pixel_collides(float x, float y)
 {
        int l, t;
        Sprite **sq;
+       Sprite *ret;
 
        l = (x + grid_size) / grid_size; t = (y + grid_size) / grid_size;
        sq = &sprites[set][l + t*gw];
-       if(pixel_hit_in_square(*sq, x, y)) return true;
-       if(l > 0 && pixel_hit_in_square(*(sq-1), x, y)) return true;
-       if(t > 0 && pixel_hit_in_square(*(sq-gw), x, y)) return true;
-       if(l > 0 && t > 0 && pixel_hit_in_square(*(sq-1-gw), x, y)) return true;
-       return false;
+       if((ret = pixel_hit_in_square(*sq, x, y))) return ret;
+       if(l > 0 && (ret = pixel_hit_in_square(*(sq-1), x, y))) return ret;
+       if(t > 0 && (ret = pixel_hit_in_square(*(sq-gw), x, y))) return ret;
+       if(l > 0 && t > 0 && (ret = pixel_hit_in_square(*(sq-1-gw), x, y))) return ret;
+       return 0;
 }
 
 
-static float
+float
 sprite_mass(Sprite *s)
 {
        if(s->type == SHIP) return s->area;
-       else if(s->type == ROCK) return 3*s->area;
+       else if(s->type == ROCK) return 3 * s->area;
        else return 0;
 }
 
@@ -339,8 +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);
@@ -351,10 +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);
 }