Hell with post-effects alpha-blending [SOLVED]

Bugs
#1

I create render target for blur post effect.
It works.
BUT all hell breaks loose when i change alpha of render target…

Crazy-Alpha-Blend.zip (6.5 MB)

…please, help me understand what i do wrong.

#2

Did you manage to solve this?

#3

Yes. The problem was solved by small shader fix.

Original shader math

result_color_RGBA.w = blur.w;

replaced by

result_color_RGBA *= blur;

Possibly, it’s problem was produced by kind of premultipled apla behavior.
In example, in DX HLSL this shader works correctly.

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