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

Premultiply the alpha on a block of pixels.

== Syntax ==

<syntaxhighlight lang='c'>
int SDL_PremultiplyAlpha(int width, int height,
                         Uint32 src_format,
                         const void * src, int src_pitch,
                         Uint32 dst_format,
                         void * dst, int dst_pitch);
</syntaxhighlight>

== Function Parameters ==

{|
|'''width'''
|the width of the block to convert, in pixels
|-
|'''height'''
|the height of the block to convert, in pixels
|-
|'''src_format'''
|an [[SDL_PixelFormatEnum]] value of the <code>src</code> pixels format
|-
|'''src'''
|a pointer to the source pixels
|-
|'''src_pitch'''
|the pitch of the source pixels, in bytes
|-
|'''dst_format'''
|an [[SDL_PixelFormatEnum]] value of the <code>dst</code> pixels format
|-
|'''dst'''
|a pointer to be filled in with premultiplied pixel data
|-
|'''dst_pitch'''
|the pitch of the destination pixels, in bytes
|}

== Return Value ==

Returns 0 on success or a negative error code on failure; call
[[SDL_GetError]]() for more information.

== Remarks ==

This is safe to use with src == dst, but not for other overlapping areas.

This function is currently only implemented for
[[SDL_PIXELFORMAT_ARGB8888]].

== Version ==

This function is available since SDL 2.0.18.

----
[[CategoryAPI]]