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Enhancements for SDL_PremultiplyAlpha()

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The function can now convert between pixels of different formats, and takes a parameter to control whether the premultiplication is done in sRGB or linear space.

Also added SDL_PremultiplySurfaceAlpha(), which can premultiply the pixels of a surface in-place.
This commit is contained in:
Sam Lantinga
2024-07-17 12:50:56 -07:00
parent b99ea1ff75
commit 334962b056
7 changed files with 210 additions and 31 deletions
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19
include/SDL3/SDL_surface.h
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@@ -798,8 +798,6 @@ extern SDL_DECLSPEC int SDLCALL SDL_ConvertPixelsAndColorspace(int width, int he
*
* 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_PixelFormat value of the `src` pixels format.
@@ -808,12 +806,27 @@ extern SDL_DECLSPEC int SDLCALL SDL_ConvertPixelsAndColorspace(int width, int he
* \param dst_format an SDL_PixelFormat 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.
* \param linear SDL_TRUE to convert from sRGB to linear space for the alpha multiplication, SDL_FALSE to do multiplication in sRGB space.
* \returns 0 on success or a negative error code on failure; call
* SDL_GetError() for more information.
*
* \since This function is available since SDL 3.0.0.
*/
extern SDL_DECLSPEC int SDLCALL SDL_PremultiplyAlpha(int width, int height, SDL_PixelFormat src_format, const void *src, int src_pitch, SDL_PixelFormat dst_format, void *dst, int dst_pitch);
extern SDL_DECLSPEC int SDLCALL SDL_PremultiplyAlpha(int width, int height, SDL_PixelFormat src_format, const void *src, int src_pitch, SDL_PixelFormat dst_format, void *dst, int dst_pitch, SDL_bool linear);
/**
* Premultiply the alpha in a surface.
*
* This is safe to use with src == dst, but not for other overlapping areas.
*
* \param surface the surface to modify.
* \param linear SDL_TRUE to convert from sRGB to linear space for the alpha multiplication, SDL_FALSE to do multiplication in sRGB space.
* \returns 0 on success or a negative error code on failure; call
* SDL_GetError() for more information.
*
* \since This function is available since SDL 3.0.0.
*/
extern SDL_DECLSPEC int SDLCALL SDL_PremultiplySurfaceAlpha(SDL_Surface *surface, SDL_bool linear);
/**
* Perform a fast fill of a rectangle with a specific color.