###### (This is the legacy documentation for SDL2, the previous stable version; [SDL3](https://wiki.libsdl.org/SDL3/) is the current stable version.)
# SDL_SetSurfaceAlphaMod

Set an additional alpha value used in blit operations.

## Header File

Defined in [SDL_surface.h](https://github.com/libsdl-org/SDL/blob/SDL2/include/SDL_surface.h)

## Syntax

```c
int SDL_SetSurfaceAlphaMod(SDL_Surface * surface,
                           Uint8 alpha);
```

## Function Parameters

|                              |             |                                                     |
| ---------------------------- | ----------- | --------------------------------------------------- |
| [SDL_Surface](SDL_Surface) * | **surface** | the [SDL_Surface](SDL_Surface) structure to update. |
| Uint8                        | **alpha**   | the alpha value multiplied into blit operations.    |

## Return Value

(int) 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.

## See Also

- [SDL_GetSurfaceAlphaMod](SDL_GetSurfaceAlphaMod)
- [SDL_SetSurfaceColorMod](SDL_SetSurfaceColorMod)

----
[CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction), [CategorySurface](CategorySurface)