rewording bounce calculations.

[vor.git] / sprite.c

diff --git a/sprite.c b/sprite.c
index 38dae30..0a6ab87 100644 (file)
--- a/sprite.c
+++ b/sprite.c
@@ -1,3 +1,4 @@
+#include <math.h>
 #include <stdlib.h>
 #include <string.h>
 #include "config.h"
@@ -32,6 +33,7 @@ get_shape(Sprite *s)
        uint16_t *px, transp;
        uint32_t bits = 0, bit, *p;
 
+       s->area = 0;
        if(s->image->format->BytesPerPixel != 2) {
                fprintf(stderr, "get_shape(): not a 16-bit image!\n");
                exit(1);
@@ -54,7 +56,7 @@ get_shape(Sprite *s)
                bit = 0;
                for(x=0; x<s->image->w; x++) {
                        if(!bit) { bits = 0; bit = 0x80000000; }
-                       if(*px++ != transp) { bits |= bit; }
+                       if(*px++ != transp) { bits |= bit; s->area++; }
                        bit >>= 1;
                        if(!bit || x == s->image->w - 1) { *(p++) = bits; }
                }
@@ -204,26 +206,26 @@ collide(Sprite *a, Sprite *b)
        xov = max(min(a->w - dx, b->w), 0);
 
        if(dy >= 0) yov = max(min(a->h - dy, b->h), 0);
-       else yov = -max(min(a->h - -dy, b->h), 0);
+       else yov = -max(min(b->h - -dy, a->h), 0);
 
        if(xov == 0 || yov == 0) return false;
        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 +233,21 @@ 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 +285,36 @@ pixel_collides(float x, float y)
        if(l > 0 && t > 0 && pixel_hit_in_square(*(sq-1-gw), x, y)) return true;
        return false;
 }
+
+
+float
+sprite_mass(Sprite *s)
+{
+       if(s->type == SHIP_SPRITE) return s->area;
+       else if(s->type == ROCK_SPRITE) return 3*s->area;
+       else return 0;
+}
+
+void
+bounce(Sprite *a, Sprite *b)
+{
+       float x, y, n;
+       float va, vb;
+       float ma, mb, mr;
+
+       // (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);
+       y = (b->y + b->h / 2) - (a->y + a->h / 2);
+       n = sqrt(x*x + y*y); x /= n; y /= n;
+
+       // velocities along (x, y), or 0 if already moving away.
+       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;
+
+       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;
+}