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<base href="https://bugs.freedesktop.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Geometry Shader - Incorrect Output"
href="https://bugs.freedesktop.org/show_bug.cgi?id=99843">99843</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Geometry Shader - Incorrect Output
</td>
</tr>
<tr>
<th>Product</th>
<td>Mesa
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>x86-64 (AMD64)
</td>
</tr>
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<th>OS</th>
<td>Linux (All)
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>medium
</td>
</tr>
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<th>Component</th>
<td>Drivers/Gallium/radeonsi
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dri-devel@lists.freedesktop.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>dan@jerber.co.uk
</td>
</tr>
<tr>
<th>QA Contact</th>
<td>dri-devel@lists.freedesktop.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=129684" name="attach_129684" title="Typical output">attachment 129684</a> <a href="attachment.cgi?id=129684&action=edit" title="Typical output">[details]</a></span>
Typical output
Hi,
I am developing a cross-platform application. I have recently found an issue
that is only present when it is tested on a Ubuntu machine. I have managed to
find a minimal example that shows the issue as follows:
The vertex shader:
#version 150
in vec2 pos;
void main(void)
{
gl_Position = vec4(pos, 0.0, 1.0);
}
The fragment shader:
#version 150
out vec4 outColour;
void main(void)
{
outColour = vec4(1.0f, 1.0f, 1.0f, 1.0f);
}
The geometry shader:
#version 150
layout(points) in;
layout(line_strip, max_vertices = 13) out;
uniform mat4 vpMatrix;
void main()
{
for(int i = 0; i < 13; i++)
{
float polygonAngle = (i * 30) + 90.0f;
vec4 vertexPosition = vec4((sin(radians(polygonAngle)) * 0.5f) +
gl_in[0].gl_Position.x, (cos(radians(polygonAngle)) * 0.5f) +
gl_in[0].gl_Position.y, 0.0f, 1.0f);
gl_Position = vpMatrix * vertexPosition;
EmitVertex();
}
EndPrimitive();
}
The problem occurs when the shader program is used with multiple VBO's. For
example:
3 separate VBO's are created with {-1.0f, 1.0f}, {1.0f, 1.0f}, {1.0f, -1.0f} as
the data. Then, for each repaint:
for(int i = 0; i < 3; i++)
{
Bind array buffer i.
glDrawArrays(GL_POINTS, 0, 1);
}
This produces strange results for the third polygon (shown in the attached
image Output.JPG).
If tested on a Windows 10 machine (exactly the same hardware) or an OSX
machine, the results are as expected (3 regular polygons with 12 sides).</pre>
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</p>
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