<html>
<head>
<base href="https://bugs.freedesktop.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Adding a uniform-dependent if-statement in shader renders a different image"
href="https://bugs.freedesktop.org/show_bug.cgi?id=111006">111006</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Adding a uniform-dependent if-statement in shader renders a different image
</td>
</tr>
<tr>
<th>Product</th>
<td>Mesa
</td>
</tr>
<tr>
<th>Version</th>
<td>git
</td>
</tr>
<tr>
<th>Hardware</th>
<td>x86-64 (AMD64)
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux (All)
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>medium
</td>
</tr>
<tr>
<th>Component</th>
<td>glsl-compiler
</td>
</tr>
<tr>
<th>Assignee</th>
<td>mesa-dev@lists.freedesktop.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>abelbriggs1@hotmail.com
</td>
</tr>
<tr>
<th>QA Contact</th>
<td>intel-3d-bugs@lists.freedesktop.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=144639" name="attach_144639" title="Reproduction shader_test files, images and diff">attachment 144639</a> <a href="attachment.cgi?id=144639&action=edit" title="Reproduction shader_test files, images and diff">[details]</a></span>
Reproduction shader_test files, images and diff
The attached archive contains two shaders, a reference shader and a variant
shader, that by construction should render the same image. On the build and PC
specified below, however, these shaders render different images. Images of the
shaders’ output are also supplied in the archive, as well as the minor diff
between the source code of the two shaders.
The difference between the two shaders is that the variant saves the current
value of GLF_color, then sets it to a random value. Then, depending on a
condition that is always true at runtime, GLF_color is overwritten with its
original value.
11a12,13
<span class="quote">> uniform vec2 injectionSwitch;
> </span >
20,22c22,23
< float width = 256.0;
< float c_re = 0.8 * (xCoord - width / 2.0) * 4.0 / width - 0.4;
< float c_im = 0.8 * (yCoord - 256.0 / 2.0) * 4.0 / width;
---
<span class="quote">> float c_re = 0.8 * (xCoord - 256.0 / 2.0) * 4.0 / 256.0 - 0.4;
> float c_im = 0.8 * (yCoord - 256.0 / 2.0) * 4.0 / 256.0;</span >
32a34,40
<span class="quote">> vec4 _GLF_outVarBackup_GLF_color;
> _GLF_outVarBackup_GLF_color = _GLF_color;
> _GLF_color = vec4(2799.7886, 1762.3462, - 8612.3800, - 7.8);
> if(((0.0 < injectionSwitch.y)))
> {
> _GLF_color = _GLF_outVarBackup_GLF_color;
> }</span >
79a88
<span class="quote">> </span >
80a90
<span class="quote">> uniform vec2 injectionSwitch 0.0 1.0</span >
The value of injectionSwitch is set to (0.0, 1.0), ensuring that the
conditional (0.0 < injectionSwitch.y) is always true at runtime. Notably, if
you remove injectionSwitch and replace the condition with ‘true’, the variant
renders the same image as the reference.
Steps to reproduce:
-------------------------------------------------------------------------------
Obtain and build piglit, the Mesa OpenGL test suite runner:
<a href="https://gitlab.freedesktop.org/mesa/piglit">https://gitlab.freedesktop.org/mesa/piglit</a>
Download the attached archive.
>From a terminal, execute the supplied tests with the piglit GLES3 shader
runner:
$ bin/shader_runner_gles3 reference.shader_test
$ bin/shader_runner_gles3 variant.shader_test
Expected results:
-------------------------------------------------------------------------------
Both tests should produce an image like reference.png.
Actual results:
-------------------------------------------------------------------------------
The variant produces a different image even though it should run exactly the
same as the reference shader. Even though the variant swaps out GLF_color and
swaps it back in, the two shaders are semantically equivalent, and there should
be no difference in their rendering. Despite this, the variant renders many of
the colored pixels in the image as transparent.
Build & PC specs:
-------------------------------------------------------------------------------
CPU: Intel Core i7-5820k
GPU: nVIDIA GTX 970
OS: Ubuntu 19.04
libdrm: git-5db0f7692d1fdf05f9f6c0c02ffa5a5f4379c1f3
Mesa: git-d4575c3071 (most recent as of this writing)
Xf86-video-nouveau: 1.0.16
Linux kernel version: 5.0.0-16-generic
This bug was found with GraphicsFuzz: <a href="https://github.com/google/graphicsfuzz">https://github.com/google/graphicsfuzz</a></pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are the assignee for the bug.</li>
</ul>
</body>
</html>