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sdl_locksurface(3) [redhat man page]

SDL_LockSurface(3)						 SDL API Reference						SDL_LockSurface(3)

NAME
SDL_LockSurface- Lock a surface for directly access. SYNOPSIS
#include "SDL.h" int SDL_LockSurface(SDL_Surface *surface); DESCRIPTION
SDL_LockSurface sets up a surface for directly accessing the pixels. Between calls to SDL_LockSurface and SDL_UnlockSurface, you can write to and read from surface->pixels, using the pixel format stored in surface->format. Once you are done accessing the surface, you should use SDL_UnlockSurface to release it. Not all surfaces require locking. If SDL_MUSTLOCK(surface) evaluates to 0, then you can read and write to the surface at any time, and the pixel format of the surface will not change. No operating system or library calls should be made between lock/unlock pairs, as critical system locks may be held during this time. It should be noted, that since SDL 1.1.8 surface locks are recursive. This means that you can lock a surface multiple times, but each lock must have a match unlock. . . SDL_LockSurface( surface ); . /* Surface is locked */ /* Direct pixel access on surface here */ . SDL_LockSurface( surface ); . /* More direct pixel access on surface */ . SDL_UnlockSurface( surface ); /* Surface is still locked */ /* Note: Is versions < 1.1.8, the surface would have been */ /* no longer locked at this stage */ . SDL_UnlockSurface( surface ); /* Surface is now unlocked */ . . RETURN VALUE
SDL_LockSurface returns 0, or -1 if the surface couldn't be locked. SEE ALSO
SDL_UnlockSurface SDL
Tue 11 Sep 2001, 23:01 SDL_LockSurface(3)

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SDL_BlitSurface(3)						 SDL API Reference						SDL_BlitSurface(3)

NAME
SDL_BlitSurface - This performs a fast blit from the source surface to the destination surface. 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. SEE ALSO
SDL_LockSurface, SDL_FillRect, SDL_Surface, SDL_Rect SDL
Tue 11 Sep 2001, 23:01 SDL_BlitSurface(3)

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