sdl_displayformatalpha(3) [redhat man page]

SDL_DisplayFormatAlpha(3)					 SDL API Reference					 SDL_DisplayFormatAlpha(3)

NAME

       SDL_DisplayFormatAlpha- Convert a surface to the display format

SYNOPSIS

       #include "SDL.h"

       SDL_Surface *SDL_DisplayFormatAlpha(SDL_Surface *surface);

DESCRIPTION

       This function takes a surface and copies it to a new surface of the pixel format and colors of the video framebuffer plus an alpha channel,
       suitable for fast blitting onto the display surface. It calls SDL_ConvertSurface

       If you want to take advantage of hardware colorkey or alpha blit acceleration, you should set the colorkey and alpha value  before  calling
       this function.

       This function can be used to convert a colourkey to an alpha channel, if the SDL_SRCCOLORKEY flag is set on the surface. The generated sur-
       face will then be transparent (alpha=0) where the pixels match the colourkey, and opaque (alpha=255) elsewhere.

RETURN VALUE

       If the conversion fails or runs out of memory, it returns NULL

SEE ALSO

       SDL_ConvertSurface, SDL_SetAlpha, SDL_SetColorKey, SDL_DisplayFormat, SDL_Surface

SDL
							      Tue 11 Sep 2001, 23:01					 SDL_DisplayFormatAlpha(3)

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)