Passing an SDL_Surface or clip_rect - c++

Question

I'm trying to write a bit of code in which I check to see if the mouse has been clicked on a certain SDL Surface. In the code example below, I have the SDL_Surface background which I am trying to check against the mouse position.
bool checkCollide(int myx, int myy, SDL_Surface* objectOne){
if(myx < objectOne->clip_rect.x) return false;
if(myx > objectOne->clip_rect.x + objectOne->clip_rect.w) return false;
if(myy < objectOne->clip_rect.y) return false;
if(myy > (objectOne->clip_rect.y + objectOne->clip_rect.h)) return false;
return true;
}
void main(){
SDL_Surface* background;
while(SDL_PollEvent(&event)){
if(event.type == SDL_MOUSEBUTTONDOWN){
if(checkCollide(event.button.x, event.button.y, background){
// run events
}
}
}
The problem I'm having is that when I try to run it as shown above, the code compiles fine but doesn't do anything. The collision check always fails. I have tried it in a lot of various combinations, including changing the parameters of checkCollide to SDL_Rect and passing the Surface's clip_rect property. The only completely successful way I've done it is to have a separate SDL_Rect with the same size and location as the SDL_Surface, and to check the collision against that. When I run it that way, it all works as I expect it to. Why isn't the surface (or clip_rect) passing correctly, or if it is, what am I doing wrong in the checkCollide function to cause it to fail?

Answer 1

The clip_rect property is not what you think it is:
From the SDL docs:
The clip_rect field is the clipping rectangle as set by
SDL_SetClipRect.
and SDL_SetClipRect
Sets the clipping rectangle for a surface. When this surface is the
destination of a blit, only the area within the clip rectangle will be
drawn into.
The rectangle pointed to by rect will be clipped to the edges of the
surface so that the clip rectangle for a surface can never fall
outside the edges of the surface.
If rect is NULL the clipping rectangle will be set to the full size of
the surface.
The problem is, that when you test the collision later on, the clip_rect x,y are always set to 0. The surface itself does not know about it's position on the screen.
A solution to this would be to create a Sprite like class that will have a Rect and a Surface.