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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
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9
src/video/directfb/SDL_DirectFB_render.c
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@@ -199,6 +199,14 @@ SetBlendMode(DirectFB_RenderData * data, int blendMode,
break;
}
case SDL_BLENDMODE_MUL:
data->blitFlags = DSBLIT_BLEND_ALPHACHANNEL;
data->drawFlags = DSDRAW_BLEND;
SDL_DFB_CHECK(destsurf->SetSrcBlendFunction(destsurf, DSBF_DSTCOLOR));
SDL_DFB_CHECK(destsurf->SetDstBlendFunction(destsurf, DSBF_INVSRCALPHA));
break;
}
data->lastBlendMode = blendMode;
}
}
@@ -223,6 +231,7 @@ PrepareDraw(SDL_Renderer * renderer, const SDL_RenderCommand *cmd)
break;
case SDL_BLENDMODE_ADD:
case SDL_BLENDMODE_MOD:
case SDL_BLENDMODE_MUL:
r = ((int) r * (int) a) / 255;
g = ((int) g * (int) a) / 255;
b = ((int) b * (int) a) / 255;