//-----------------------------------------------------------------------------
int SDL_CollidePixel(SDL_Surface *as , int ax , int ay , SDL_Surface *bs , int bx , int by, int skip)
{
int ax1 = ax + as->w - 1;
int ay1 = ay + as->h - 1;
int bx1 = bx + bs->w - 1;
int by1 = by + bs->h - 1;
if((bx1 < ax) || (ax1 < bx))
{
return false;
}
if((by1 < ay) || (ay1 < by))
{
return false;
}
int xstart = SDL_COLLIDE_MAX(ax,bx);
int xend = SDL_COLLIDE_MIN(ax1,bx1);
int ystart = SDL_COLLIDE_MAX(ay,by);
int yend = SDL_COLLIDE_MIN(ay1,by1);
for(int y = ystart ; y <= yend ; y += skip)
{
for(int x = xstart ; x <= xend ; x += skip)
{
if(!SDL_CollideTransparentPixel(as , x-ax , y-ay) && !SDL_CollideTransparentPixel(bs , x-bx , y-by))
return 1;
}
}
return 0;
}
/*
SDL pixel perfect collision test
*/
int SDL_CollidePixel(SDL_Surface *as , int ax , int ay ,
SDL_Surface *bs , int bx , int by, int skip)
{
/*a - bottom right co-ordinates in world space*/
int ax1 = ax + as->w - 1;
int ay1 = ay + as->h - 1;
/*b - bottom right co-ordinates in world space*/
int bx1 = bx + bs->w - 1;
int by1 = by + bs->h - 1;
/*check if bounding boxes intersect*/
if((bx1 < ax) || (ax1 < bx))
return 0;
if((by1 < ay) || (ay1 < by))
return 0;
/*Now lets make the bouding box for which we check for a pixel collision*/
/*To get the bounding box we do
Ax1,Ay1______________
| |
| |
| |
| Bx1,By1____________
| | | |
| | | |
|________|_______| |
| Ax2,Ay2 |
| |
| |
|___________Bx2,By2
To find that overlap we find the biggest left hand cordinate
AND the smallest right hand co-ordinate
To find it for y we do the biggest top y value
AND the smallest bottom y value
Therefore the overlap here is Bx1,By1 --> Ax2,Ay2
Remember Ax2 = Ax1 + SA->w
Bx2 = Bx1 + SB->w
Ay2 = Ay1 + SA->h
By2 = By1 + SB->h
*/
/*now we loop round every pixel in area of
intersection
if 2 pixels alpha values on 2 surfaces at the
same place != 0 then we have a collision*/
int xstart = SDL_COLLIDE_MAX(ax,bx);
int xend = SDL_COLLIDE_MIN(ax1,bx1);
int ystart = SDL_COLLIDE_MAX(ay,by);
int yend = SDL_COLLIDE_MIN(ay1,by1);
for(int y = ystart ; y <= yend ; y += skip)
{
for(int x = xstart ; x <= xend ; x += skip)
{
/*compute offsets for surface
before pass to TransparentPixel test*/
if(!SDL_CollideTransparentPixel(as , x-ax , y-ay)
&& !SDL_CollideTransparentPixel(bs , x-bx , y-by))
return 1;
}
}
return 0;
}
