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);
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; }
}
}
void
+reset_sprites(void)
+{
+ int i;
+
+ for(i=0; i<gw*gh; i++)
+ while(sprites[set][i]) {
+ Sprite *s = remove_sprite(&sprites[set][i]);
+ insert_sprite(&free_sprites[s->type], s);
+ s->flags = 0;
+ }
+}
+
+void
move_sprite(Sprite *s)
{
- // move it.
- s->x += (s->dx - screendx)*t_frame;
- s->y += (s->dy - screendy)*t_frame;
+ if(s->flags & MOVE) {
+ s->x += (s->dx - screendx)*t_frame;
+ s->y += (s->dy - screendy)*t_frame;
+ }
}
void
if(s->x + s->w < 0 || s->x >= XSIZE
|| s->y + s->h < 0 || s->y >= YSIZE) {
insert_sprite(&free_sprites[s->type], s);
- s->type = NONE;
+ s->flags = 0;
} else insert_sprite(square(s->x, s->y, 1-set), s);
}
int sq;
Sprite **head;
- // Move all the sprites (position and set)
+ // Move all the sprites
for(sq=0; sq<gw*gh; sq++) {
head=&sprites[set][sq];
while(*head) {
{
int dx, dy, xov, yov;
+ if(!COLLIDES(a) || !COLLIDES(b)) return false;
+
if(b->x < a->x) { Sprite *tmp = a; a = b; b = tmp; }
dx = b->x - a->x;
else return mask_collide(xov, yov, a, b);
}
+void
+collide_with_list(Sprite *s, Sprite *list)
+{
+ for(; list; list=list->next)
+ if(collide(s, list)) do_collision(s, list);
+}
+
+void
+collisions(void)
+{
+ int i, end = gw*gh;
+ Sprite *s;
+ for(i=0; i<end; i++) {
+ for(s=sprites[set][i]; s; s=s->next) {
+ collide_with_list(s, s->next);
+ if(i+1 < end) collide_with_list(s, sprites[set][i+1]);
+ if(i+gw < end) collide_with_list(s, sprites[set][i+gw]);
+ if(i+gw+1 < end) collide_with_list(s, sprites[set][i+gw+1]);
+ }
+ }
+}
+
Sprite *
hit_in_square(Sprite *r, Sprite *s)
{
pixel_collide(Sprite *s, int x, int y)
{
uint32_t pmask;
+
+ if(!COLLIDES(s)) return false;
if(x < s->x || y < s->y || x >= s->x + s->w || y >= s->y + s->h) return 0;
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(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;
}
+
+float
+sprite_mass(Sprite *s)
+{
+ if(s->type == SHIP) return s->area;
+ else if(s->type == ROCK) return 3 * s->area;
+ else return 0;
+}
+
+/*
+ * BOUNCE THEORY
+ *
+ * ****************** In 1 Dimension *****************
+ *
+ * For now we will imagine bouncing A and B off each other in 1 dimension (along
+ * a line). We can safely save the other dimension for later.
+ *
+ * A and B are the same weight, and are both traveling 1m/sec, to collide right
+ * at the origin. With perfect bounciness, their full momentum is reversed.
+ *
+ * If we cut the weight of A down by half, then the center of our colision will
+ * drift towards A (the speeds of A and B are not simply reversed as in our last
+ * example.) However, there is always a place between A and B on the line (I'll
+ * call it x) such that the speeds of A and B relative to x, are simply
+ * reversed. Thus we can find the new speed for A like so:
+ *
+ * new A = x -(A - x)
+ *
+ * new B = x -(B - x)
+ *
+ * or, simply:
+ *
+ * new A = 2x - A
+ *
+ * new B = 2x - B
+ *
+ *
+ * this point x is the sort of center of momentum. If, instead of bouncing, A
+ * and B just globbed together, x would be center of the new glob.
+ *
+ * x is the point where there's an equal amount of force coming in from both
+ * sides. ie the weighted average of the speeds of A and B.
+ *
+ * average force = (A force + B force) / total mass
+ *
+ * x.speed = (a.speed * a.mass + b.speed * b.mass) / (a.mass + b.mas)
+ *
+ * then we apply the formula above for calculating the new A and B.
+ *
+ *
+ *
+ *
+ * ****************** In 2 Dimensions *****************
+ *
+ * OK, that's how we do it in 1D. Now we need to deal with 2D.
+ *
+ * Imagine (or draw) the two balls just as they are bouncing off each other.
+ * Imagine drawing a line through the centers of the balls. The balls are
+ * exerting force on each other only along this axis. So if we rotate
+ * everything, we can do our earlier 1D math along this line.
+ *
+ * It doesn't matter what direction the balls are going in, they only exert
+ * force on each other along this line. What we will do is to compute the part
+ * of the balls' momentum that is going along this line, and bounce it according
+ * to our math above. The other part is unaffected by the bounce, and we can
+ * just leave it alone.
+ *
+ * To get this component of the balls' momentum, we can use the dot product.
+ *
+ * dot(U, V) = length(U) * length(V) * cos(angle between U and V)
+ *
+ * If U is a length 1 vector, then dot(U, V) is the length of the component of V
+ * in the direction of U. So the components of V are:
+ *
+ * U * dot(U, V) parallel to U
+ *
+ * V - U * dot(U, V) perpendicular to U
+ *
+ * To do the actual bounce, we compute the unit vector between the center of the
+ * two balls, compute the components of the balls' speeds along this vector (A
+ * and B), and then bounce them according to the math above:
+ *
+ * new A = 2x - A
+ *
+ * new B = 2x - B
+ *
+ * But we rewrite it in relative terms:
+ *
+ * new A = A + 2(x-A)
+ *
+ * new B = B + 2(x-B)
+ */
+
void
bounce(Sprite *a, Sprite *b)
{
- float x, y, n;
- float na, nb;
+ float x, y, n; // (x, y) is unit vector from a to b.
+ float va, vb; // va, vb are balls' speeds along (x, y)
+ float ma, mb; // ma, mb are the balls' masses.
+ float vc; // vc is the "center of momentum"
+ // (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;
- na = (x*a->dx + y*a->dy); // sqrt(a->dx*a->dx + a->dy*a->dy);
- nb = (x*b->dx + y*b->dy); // sqrt(b->dx*b->dx + b->dy*b->dy);
+ // velocities along (x, y)
+ va = x*a->dx + y*a->dy;
+ vb = x*b->dx + y*b->dy;
+ if(vb-va > 0) return; // don't bounce if we're already moving away.
+
+ // get masses and compute "center" speed
+ ma = sprite_mass(a); mb = sprite_mass(b);
+ vc = (va*ma + vb*mb) / (ma+mb);
- a->dx += x*(nb-na); a->dy += y*(nb-na);
- b->dx += x*(na-nb); b->dy += y*(na-nb);
+ // bounce off the center speed.
+ a->dx += 2*x*(vc-va); a->dy += 2*y*(vc-va);
+ b->dx += 2*x*(vc-vb); b->dy += 2*y*(vc-vb);
}
Got questions, comments, patches, etc.? Contact Jason Woofenden