[Mesa-dev] [Bug 99919] Wrong and unstable image rendering from GLSL fragment shaders

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99919

            Bug ID: 99919
           Summary: Wrong and unstable image rendering from GLSL fragment
                    shaders
           Product: Mesa
           Version: 17.0
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Mesa core
          Assignee: mesa-dev at lists.freedesktop.org
          Reporter: h.evrard at imperial.ac.uk
        QA Contact: mesa-dev at lists.freedesktop.org

Created attachment 129862
  --> https://bugs.freedesktop.org/attachment.cgi?id=129862&action=edit
Archive with pair of shaders and their expected renderings

Steps to Reproduce:
-------------------------------

1. Obtain and build the latest release of get-image, a simple tool that
   creates a .png image from a fragment shader
   https://github.com/mc-imperial/get-image

2. From a terminal, execute:

   /path/to/get_image/linux_out/install/bin/get_image original.frag

   This will create output.png, which should look like original.png

3. From a terminal, execute:

   /path/to/get_image/linux_out/install/bin/get_image variant.frag

   This will create output.png, which should look like variant.png

Expected Results:
-------------------------------

Both shaders should render an image that looks like original.png.  This
is because the only difference between the .frag files is:

- a for loop of 1 iteration

- inside this loop, a "if" which condition is sure to be false at
  runtime (we control the value of injectionSwitch to ensure this)

Actual Results:
-------------------------------
The shaders render completely different images, which they should not.
Moreover, the variant.frag file rendering seems unstable, i.e. it does
not always render the same image, but it always renders an image
different from the expected one.

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