[SDL] SDL 2D Rotation

[wolf1oo]

Well, I had been looking for a couple of days for ways to rotate parts of images etc. with the SDL library, but I only found that people said to use the opengl rotate functions.
I didn't quite like this alternative  :P 

So, here is what I came up with.


Code:
void SDL_Rotate(SDL_Surface *surface, SDL_Rect *rect, float angle, int x, int y) {
	SDL_LockSurface(surface);
	int bpp = surface->format->BytesPerPixel;
	int white = SDL_MapRGB(surface->format,0xff,0xff,0xff);
	char* pixels = (char*)malloc(surface->w*surface->h*bpp);
	for (int i = surface->w*surface->h; i >= 0; --i) {
		char* c = pixels+i*bpp;
		memcpy(c,&white,bpp);
	}
	for(int sx = surface->w; sx >= 0; --sx) {
		for (int sy = surface->h; sy >= 0; --sy) {
			if (sx >= rect->x && sx < (rect->x+rect->w) && sy >= rect->y && sy < (rect->y+rect->h)) { //Point in surface is part of rect
				float curangle;
				if (sx-x == 0) {curangle = 90;}
				else {curangle = atan((float)(sy-y)/(float)(sx-x)) * 180/3.14159;}
				float l = sqrt(pow(sx-x,2)+pow(sy-y,2));
				char* p = (char*)surface->pixels+sx*bpp+sy*surface->pitch;
				char* q = (char*)pixels+((int)(cos((angle+curangle)*3.14159/180)*l)+x)*bpp+((int)(sin((angle+curangle)*3.14159/180)*l)+y)*surface->pitch;
				memcpy(q,p,bpp);
				if(memcmp(q+bpp,&white,bpp) == 0) {
					memcpy(q+bpp,q,bpp); //To effectively cover without many/any holes
				}
			}
		}
	}
	memcpy(surface->pixels,pixels,surface->w*surface->h*bpp);
	SDL_UnlockSurface(surface);
}



As you can see, it only really needs the normal C math library. Other than that, its pretty straightforward and heeds pretty good results, if you want to rotate without getting to nit-picky in detail. The arguments are pretty obvious, and x and y describes the point of rotation. The surface of course must be updated afterward as well.

With my luck it has probably already been done before, as I expect it has, but I was unable to find it. But just in case others needed some reference.....




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.libsdl.org/pipermail/sdl-libsdl.org/attachments/20100322/486ca85f/attachment.htm>