libsegl/sdlfuncs.cpp

#include "sdlfuncs.h"

namespace segl {

Uint32 getPixel(SDL_Surface *surface, int x, int y)
{
    int bpp = surface->format->BytesPerPixel;
    /* Here p is the address to the pixel we want to retrieve */
    Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

    switch(bpp) {
    case 1:
        return *p;

    case 2:
        return *(Uint16 *)p;

    case 3:
        if(SDL_BYTEORDER == SDL_BIG_ENDIAN)
            return p[0] << 16 | p[1] << 8 | p[2];
        else
            return p[0] | p[1] << 8 | p[2] << 16;

    case 4:
        return *(Uint32 *)p;

    default:
        return 0;       /* shouldn't happen, but avoids warnings */
    }
}

void setPixel(SDL_Surface *surface, int x, int y, Uint32 pixel)
{
    int bpp = surface->format->BytesPerPixel;
    /* Here p is the address to the pixel we want to set */
    Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;

    switch(bpp) {
    case 1:
        *p = pixel;
        break;

    case 2:
        *(Uint16 *)p = pixel;
        break;

    case 3:
        if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
            p[0] = (pixel >> 16) & 0xff;
            p[1] = (pixel >> 8) & 0xff;
            p[2] = pixel & 0xff;
        } else {
            p[0] = pixel & 0xff;
            p[1] = (pixel >> 8) & 0xff;
            p[2] = (pixel >> 16) & 0xff;
        }
        break;

    case 4:
        *(Uint32 *)p = pixel;
        break;
    }
}

void swapPixel(SDL_Surface *surface, int x1, int y1, int x2, int y2) {
	Uint32 a,b;
	a = getPixel(surface, x1, y1);
	b = getPixel(surface, x2, y2);
	
	setPixel(surface, x1, y1, b);
	setPixel(surface, x2, y2, a);
}

void mirrorSurfaceMiddleX(SDL_Surface *surface) {
	SDL_LockSurface(surface);
	int upto = surface->h / 2;

	for(int i=0; i<upto; i++) {
		for(int x=0; x<surface->w; x++) {
			swapPixel(surface, x, i, x, surface->h-1-i);
		}
	}
	SDL_UnlockSurface(surface);
}

} // namespace segl