SYNOPSIS

#include "SDL.h"

int SDL_BlitSurface(SDL_Surface *src, SDL_Rect *srcrect, SDL_Surface *dst, SDL_Rect *dstrect);

DESCRIPTION

This performs a fast blit from the source surface to the destination surface.

Only the position is used in the dstrect (the width and height are ignored).

If either srcrect or dstrect are NULL, the entire surface (src or dst) is copied.

The final blit rectangle is saved in dstrect after all clipping is performed (srcrect is not modified).

The blit function should not be called on a locked surface.

The results of blitting operations vary greatly depending on whether SDL_SRCAPLHA is set or not. See SDL_SetAlpha for an explaination of how this affects your results. Colorkeying and alpha attributes also interact with surface blitting, as the following pseudo-code should hopefully explain.

if (source surface has SDL_SRCALPHA set) {
    if (source surface has alpha channel (that is, format->Amask != 0))
        blit using per-pixel alpha, ignoring any colour key
    else {
        if (source surface has SDL_SRCCOLORKEY set)
            blit using the colour key AND the per-surface alpha value
        else
            blit using the per-surface alpha value
    }
} else {
    if (source surface has SDL_SRCCOLORKEY set)
        blit using the colour key
    else
        ordinary opaque rectangular blit
}

RETURN VALUE

If the blit is successful, it returns 0, otherwise it returns -1.

If either of the surfaces were in video memory, and the blit returns -2, the video memory was lost, so it should be reloaded with artwork and re-blitted:

        while ( SDL_BlitSurface(image, imgrect, screen, dstrect) == -2 ) {
                while ( SDL_LockSurface(image)) < 0 )
                        Sleep(10);
                -- Write image pixels to image->pixels --
                SDL_UnlockSurface(image);
        }

 This happens under DirectX 5.0 when the system switches away from your fullscreen application. Locking the surface will also fail until you have access to the video memory again.