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Added SDL_PremultiplyAlpha() to premultiply alpha on a block of SDL_PIXELFORMAT_ARGB8888 pixels

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This commit is contained in:
Sam Lantinga
2021-11-21 12:18:10 -08:00
parent 49369142bd
commit c97b721868
9 changed files with 109 additions and 34 deletions
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28
include/SDL_surface.h
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@@ -705,7 +705,7 @@ extern DECLSPEC SDL_Surface *SDLCALL SDL_ConvertSurfaceFormat
* \param height the height of the block to copy, in pixels
* \param src_format an SDL_PixelFormatEnum value of the `src` pixels format
* \param src a pointer to the source pixels
* \param src_pitch the pitch of the block to copy, in bytes
* \param src_pitch the pitch of the source pixels, in bytes
* \param dst_format an SDL_PixelFormatEnum value of the `dst` pixels format
* \param dst a pointer to be filled in with new pixel data
* \param dst_pitch the pitch of the destination pixels, in bytes
@@ -720,6 +720,32 @@ extern DECLSPEC int SDLCALL SDL_ConvertPixels(int width, int height,
Uint32 dst_format,
void * dst, int dst_pitch);
/**
* Premultiply the alpha on a block of pixels.
*
* This is safe to use with src == dst, but not for other overlapping areas.
*
* This function is currently only implemented for SDL_PIXELFORMAT_ARGB8888.
*
* \param width the width of the block to convert, in pixels
* \param height the height of the block to convert, in pixels
* \param src_format an SDL_PixelFormatEnum value of the `src` pixels format
* \param src a pointer to the source pixels
* \param src_pitch the pitch of the source pixels, in bytes
* \param dst_format an SDL_PixelFormatEnum value of the `dst` pixels format
* \param dst a pointer to be filled in with premultiplied pixel data
* \param dst_pitch the pitch of the destination pixels, in bytes
* \returns 0 on success or a negative error code on failure; call
* SDL_GetError() for more information.
*
* \since This function is available since SDL 2.0.18.
*/
extern DECLSPEC int SDLCALL SDL_PremultiplyAlpha(int width, int height,
Uint32 src_format,
const void * src, int src_pitch,
Uint32 dst_format,
void * dst, int dst_pitch);
/**
* Perform a fast fill of a rectangle with a specific color.
*