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By Design



Found in [Package]


Issue ID




[HDRP] Camera Color Alpha variable is ignored when using HDRP 5.10.0

Package: Scriptable Render Pipeline HD


How to reproduce:
1. Open the "RenderToTextureBug" Scene in the attached "" Project
2. Click on the "Camera" GameObject
3. Set clear mode to Color
4. Click on the HDRP Color picker on the Camera Component
5. Set the Color to pure red and drag Alpha Slider to the left until Alpha = 0
6. Observe the Canvas contents in the Scene View

Expected behavior: The Color of the Background is Transparent
Actual behavior: The Color is still red as if the Alpha is equal to 255

Reproducible with(Unity Versions): 2019.1.0b10, 2019.2.0a10
Reproducible with(Package Versions): 5.10.0

Not reproducible with(Unity Versions): 2018.3.12f1
Not reproducible with(Package Versions): 4.10.0

  1. Response avatar

    Resolution Note:

    As we plan to use internally the alpha channel of the color buffer for future features, we cannot support the output of alpha channel in a render texture.

Comments (13)

  1. 543d32f6337fd9fe0c264c5dcaeba78f?d=mm


    Mar 29, 2021 16:01

    Tag this as "By design" is a problem because nobody can vote for it anymore... You're saying, it's not a bug, it's a feature, but this is a removal of an existing feature. I would like to vote to add back this feature because I can't see any workaround...

  2. Ad2b89b7c0bfe6bff692fd31f59314e0?d=mm


    Jan 07, 2021 00:06

    I'm also blocked by this issue. I need to send a transparent spout feed from Unity.

  3. 28f902320dec5feac2a099a274414b53?d=mm


    Jan 30, 2020 09:29

    RenderTextures were kept behind paywalls for many years, such cool feature it once was! There is still no solution in 19.3 final.

  4. Efb0ef0e5620aaed1fa10bd8243bf127?d=mm


    Oct 24, 2019 02:20

    This is outrageous!! Alpha is needed for MANY purposes.
    Does Unity at least propose any other way of blending cameras if not through RenderTexture!?

  5. 8e787d52c8aa9515022ec5fffe8bde5b?d=mm


    Sep 13, 2019 00:57

    So in other words HDRP is a no-go? Why drop render texture support? It was such a useful thing.

  6. D5759620e7695f5355d5f469478a07f4?d=mm


    Sep 10, 2019 16:54

    This is unacceptable, Im trying my best to make HDRP work in this project, and every turn is a roadblock, or some other hack I have to do, to make it do basic things we need to do in actual development.
    For all its Hype, things like this are making dev's lives harder.
    Unity, Please Reconsider your stance on this.

  7. 67e9c87b44a5187ed5f2004670d05467?d=mm


    Aug 28, 2019 18:47

    Yes, chroma-keying is a (temporary) solution here.

    - Set the clear color of the camera to full green (0, 1, 0)
    - Clone the Default UI shader from Unity
    - Clip/discard the pixel (in the fragment shader) when the difference of the actual color (in the render texture) and the matte color (green) is below a configurable threshold.
    - Finished: a simple chroma keying UI shader.

    However, please give us back the alpha channel.

  8. D1d03a1bd07295cadf3e77c1d2b5b3d0?d=mm


    Aug 28, 2019 11:49

    So, we are asked to write a chroma keying shaders to blend a secondary camera with the scene properly?

  9. 9f9e152920c3bde8c7858b760382b812?d=mm


    Aug 23, 2019 03:07

    Why is there no other easy way to do this? Sigh.

  10. E54b7af50717acc5a97fd83cf2b1cb00?d=mm


    Aug 08, 2019 17:51

    We need the alpha change to work properly as an alpha channel. Guys... take off your engine (and cool demo) hat for a second and consider what down and dirty game development requires. You are losing touch... this is just one frustrating example.

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