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Bug Strange blending of alpha channel of opaque geometry on iOS starts from Unity 2020.3.18f

Discussion in 'General Graphics' started by st-VALVe, Nov 18, 2021.

  1. st-VALVe


    Jan 8, 2014
    Hello there!
    For a long time, we have been using the alpha channel of opaque geometry to store custom vertex data (usually for scene depth). (We are using the built-in rendering pipeline)
    And it worked great before we updated to Unity 2020.3.18f.
    But after doing that, we discovered strange behavior on several iOS devices (currently iPhone 12 and iPhone SE).
    It looks like the inverted alpha channel of the opaque geometry is adding to the RGB channels. RGB + (1 - Alpha).
    When we started looking for a solution, we found these changes that were made to the default unity particle shaders in Unity 2020.3.17f: 2.png
    So now we are using Unity 2020.3.16f and cannot update further due to this situation.
    We cannot opt out of using the alpha channel for our custom data because all of our frame optimizations are based on it. And we need any other correct solution.
    Help us, please!
  2. st-VALVe


    Jan 8, 2014
    Anyone, please? How does this forum work?
  3. bgolus


    Dec 7, 2012
    These are the community forums. If you need an official response from Unity (i.e. you think this is a bug with Unity) you should report a bug using the in editor form for it.

    You’ve honestly just not said enough about the problem for anyone to give you any kind of useful help. Are you using built in shaders, or custom ones? As you mentioned you’re using the vertex alpha presumably these are custom shaders. If you’re using custom shaders you’ll need to post the entire shader here. The fact your looking at the particles cginc makes me think you’re using that in your custom shader code, to which I would ask, why?

    If you do post your shader code here, please use the
    st-VALVe likes this.