Question BlendOp Max gives strange result (project attached)

I have simple scene with 2 unlit transparent quads rendered above unlit black background. These quads have same size and texture (Default-Particle). The only difference is that one have shader with BlendOp Add (left) and another have shader with BlendOp Max.

The question is - why the second looks bigger? I expect they should look absolutely the same, because (Color * SrcAlpha + Black * OneMinusSrcAlpha) should give the same result as MAX(Color * SrcAlpha, Black * OneMinusSrcAlpha), and in both cases the result should be (Color * SrcAlpha).

Or am I wrong??

Unity 2020.3.34, Standalone, BRP
The project attached.

 

The

BlendOp Max

and

Min

operators are unique in that they ignore the

Blend

settings. So

BlendOp Max

equates to:

Code (csharp):

1. max(Src, Dst)

regardless of what you set the

Blend

to, and not

Code (csharp):

1. max(Src * SrcAlpha, Dst * OneMinusSrcAlpha)

 

Wow, that's interesting, didn't know that. But that means that the Unity's doc is wrong. It says:

• If the blending operation is Add, Sub, RevSub, Min, or Max, the GPU multiplies the value of the output of the fragment shader by the source factor.
• If the blending operation is Add, Sub, RevSub, Min, or Max, the GPU multiplies the value that is already in the render target by the destination factor.

Is this Unity's doc really incorrect?

 

Yep.

You can try it yourself. Set the blend to:

Blend Zero One

. It won’t change how it looks.

 

That's funny. Haha Thanks for the answer!