###### (This is the legacy documentation for stable SDL2, the current stable version; [SDL3](https://wiki.libsdl.org/SDL3/) is the current development version.) # SDL_SetSurfaceAlphaMod Set an additional alpha value used in blit operations. ## Syntax ```c int SDL_SetSurfaceAlphaMod(SDL_Surface * surface, Uint8 alpha); ``` ## Function Parameters | | | | --------------- | -------------------------------------------------- | | **surface** | the [SDL_Surface](SDL_Surface) structure to update | | **alpha** | the alpha value multiplied into blit operations | ## Return Value Returns 0 on success or a negative error code on failure; call [SDL_GetError](SDL_GetError)() for more information. ## Remarks When this surface is blitted, during the blit operation the source alpha value is modulated by this alpha value according to the following formula: `srcA = srcA * (alpha / 255)` ## Version This function is available since SDL 2.0.0. ## Related Functions * [SDL_GetSurfaceAlphaMod](SDL_GetSurfaceAlphaMod) * [SDL_SetSurfaceColorMod](SDL_SetSurfaceColorMod) ---- [CategoryAPI](CategoryAPI)