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Fixed bug 4903 - Lack of color multiply with alpha (SDL_BLENDMODE_MOD + SDL_BLENDMODE_BLEND) blending mode for all renderers

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Konrad

This kind of blending is rather quite useful and in my opinion should be available for all renderers. I do need it myself, but since I didn't want to use a custom blending mode which is supported only by certain renderers (e.g. not in software which is quite important for me) I did write implementation of SDL_BLENDMODE_MUL for all renderers altogether.

SDL_BLENDMODE_MUL implements following equation:

dstRGB = (srcRGB * dstRGB) + (dstRGB * (1-srcA))
dstA = (srcA * dstA) + (dstA * (1-srcA))

Background:

https://i.imgur.com/UsYhydP.png

Blended texture:

https://i.imgur.com/0juXQcV.png

Result for SDL_BLENDMODE_MOD:

https://i.imgur.com/wgNSgUl.png

Result for SDL_BLENDMODE_MUL:

https://i.imgur.com/Veokzim.png

I think I did cover all possibilities within included patch, but I didn't write any tests for SDL_BLENDMODE_MUL, so it would be lovely if someone could do it.
This commit is contained in:
Sam Lantinga 2020-01-16 08:52:59 -08:00
parent 669729a8a0
commit 981e0d367c
19 changed files with 819 additions and 159 deletions
Download patch file Download diff file Expand all files Collapse all files

11
src/render/SDL_render.c
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@ -75,6 +75,10 @@
SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_SRC_COLOR, SDL_BLENDOPERATION_ADD, \
SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_ONE, SDL_BLENDOPERATION_ADD)
#define SDL_BLENDMODE_MUL_FULL \
SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_DST_COLOR, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA, SDL_BLENDOPERATION_ADD, \
SDL_BLENDFACTOR_DST_ALPHA, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA, SDL_BLENDOPERATION_ADD)
#if !SDL_RENDER_DISABLED
static const SDL_RenderDriver *render_drivers[] = {
#if SDL_VIDEO_RENDER_D3D
@ -970,6 +974,7 @@ IsSupportedBlendMode(SDL_Renderer * renderer, SDL_BlendMode blendMode)
case SDL_BLENDMODE_BLEND:
case SDL_BLENDMODE_ADD:
case SDL_BLENDMODE_MOD:
case SDL_BLENDMODE_MUL:
return SDL_TRUE;
default:
@ -3288,6 +3293,9 @@ SDL_GetShortBlendMode(SDL_BlendMode blendMode)
if (blendMode == SDL_BLENDMODE_MOD_FULL) {
return SDL_BLENDMODE_MOD;
}
if (blendMode == SDL_BLENDMODE_MUL_FULL) {
return SDL_BLENDMODE_MUL;
}
return blendMode;
}
@ -3306,6 +3314,9 @@ SDL_GetLongBlendMode(SDL_BlendMode blendMode)
if (blendMode == SDL_BLENDMODE_MOD) {
return SDL_BLENDMODE_MOD_FULL;
}
if (blendMode == SDL_BLENDMODE_MUL) {
return SDL_BLENDMODE_MUL_FULL;
}
return blendMode;
}