SDL accessing pixel data of SDL_Surface

Question

I want to manipulate the color of loaded images but I am having trouble when I try to backup the pixel data. My code looks something like this:

Uint32* pixels, oriPixels;
SDL_Surface* image;

void BackupPixelData()
{
    pixels = (Uint32*)image->pixels;
    oriPixels = new Uint32[image->w * image->h];
    for (int i = 0; i < image->w * image->h; i++)
    {
        oriPixels[i] = pixels[i]; //This causes an access violation midway through
        *(oriPixels + i) = *(pixels + i); //Using this method does not cause any crash, but the image will have artifacts
    }
}

I can get the code to work by changing oriPixels into a vector of Uint32, and I haven't experienced any issues doing that (the image can be restored to the original color using the oriPixels).

What should I do to properly load the pixel data?

The image is in 32 bits.

Answer 1

You must take into account data alignment. Rows may be padded depending on the surface format. Check the documentation about the pitch field of the SDL_Surface for more details https://wiki.libsdl.org/SDL_Surface .

You get the access violation because the memory buffer size is not width * height but actually pitch * height.