Question

Here’s my code:

template<typename G, typename N> void load_xbm(G* g,N w, N h,unsigned char* data)
{
    Uint32 rmask, gmask, bmask, amask;

        /* SDL interprets each pixel as a 32-bit number, so our masks must depend
           on the endianness (byte order) of the machine */
    #if SDL_BYTEORDER == SDL_BIG_ENDIAN
        rmask = 0xff000000;
        gmask = 0x00ff0000;
        bmask = 0x0000ff00;
        amask = 0x000000ff;
    #else
        rmask = 0x000000ff;
        gmask = 0x0000ff00;
        bmask = 0x00ff0000;
        amask = 0xff000000;
    #endif

    SDL_Surface* s = g->backend_surface();
    s = SDL_CreateRGBSurface(SDL_HWSURFACE,w,h,16,rmask,gmask,bmask,amask);
    g->backend_surface( s );

    for (N x = 0; x < w; x++)
    {
        for(N y = 0; y < h; y++)
        {
            g->put_pixel(x,y,data[y*x]);
        }
    }

    SDL_Flip( s );
}

g->backend_surface() just returns an SDL_Surface* member in G.
w is the width of the xbm bitmap, h is the height, data is an array of unsigned chars containing the colors of every pixel.

g->put_pixel() is a simple wrap over of the putpixel method in SDL docs, which uses it’s backend_surface as the first parameter to the example putpixel function.

Now when I execute it the program exits with 0x3. By debugging the code I’ve found that it exits on the call to the putpixel method, note that the putpixel method is working fine elsewhere. I’ve also found out that it only exits when the x and y arguments to putpixel are bigger than the original width and height of the Surface, but haven’t I resized the surface using SDL_CreateRGBSurface to the required width and height?

Answer 1

Guessing in the wild here…

This SDL tutorial example (point 2.5) says that the Surface must be locked before calling this function. Is yours?