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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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3
src/render/direct3d11/SDL_render_d3d11.c
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@@ -636,7 +636,8 @@ D3D11_CreateDeviceResources(SDL_Renderer * renderer)
/* Create blending states: */
if (!D3D11_CreateBlendState(renderer, SDL_BLENDMODE_BLEND) ||
!D3D11_CreateBlendState(renderer, SDL_BLENDMODE_ADD) ||
!D3D11_CreateBlendState(renderer, SDL_BLENDMODE_MOD)) {
!D3D11_CreateBlendState(renderer, SDL_BLENDMODE_MOD) ||
!D3D11_CreateBlendState(renderer, SDL_BLENDMODE_MUL)) {
/* D3D11_CreateBlendMode will set the SDL error, if it fails */
goto done;
}