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<HTML>
<TITLE>Viewperf Issues</TITLE>
<link rel="stylesheet" type="text/css" href="mesa.css"></head>
<BODY>
<h1>Viewperf Issues</h1>
<p>
This page lists known issues with
<a href="http://www.spec.org/gwpg/gpc.static/vp11info.html" target="_main">SPEC Viewperf 11</a>
when running on Mesa-based drivers.
</p>
<p>
The Viewperf data sets are basically GL API traces that are recorded from
CAD applications, then replayed in the Viewperf framework.
</p>
<p>
The primary problem with these traces is they blindly use features and
OpenGL extensions that were supported by the OpenGL driver when the trace
was recorded,
but there's no checks to see if those features are supported by the driver
when playing back the traces with Viewperf.
</p>
<p>
These issues have been reported to the SPEC organization in the hope that
they'll be fixed in the future.
</p>
<h2>Catia-03 test 2</h2>
<p>
This test creates over 38000 vertex buffer objects. On some systems
this can exceed the maximum number of buffer allocations. Mesa
generates GL_OUT_OF_MEMORY errors in this situation, but Viewperf
does no error checking and continues. When this happens, some drawing
commands become no-ops. This can also eventually lead to a segfault
either in Viewperf or the Mesa driver.
</p>
<h2>Catia-03 tests 3, 4, 8</h2>
<p>
These tests use features of the
<a href="http://www.opengl.org/registry/specs/NV/fragment_program2.txt"
target="_main">
GL_NV_fragment_program2</a> and
<a href="http://www.opengl.org/registry/specs/NV/vertex_program3.txt"
target="_main">
GL_NV_vertex_program3</a> extensions without checking if the driver supports
them.
</p>
<p>
When Mesa tries to compile the vertex/fragment programs it generates errors
(which Viewperf ignores).
Subsequent drawing calls become no-ops and the rendering is incorrect.
</p>
<h2>sw-02 tests 1, 2, 4</h2>
<p>
These tests depend on the
<a href="http://www.opengl.org/registry/specs/NV/primitive_restart.txt"
target="_main">GL_NV_primitive_restart</a> extension.
</p>
<p>
If the Mesa driver doesn't support this extension the rendering will
be incorrect and the test will fail.
</p>
<h2>Lightwave-01 test 3</h2>
<p>
This test uses a number of mipmapped textures, but the textures are
incomplete because the last/smallest mipmap level (1 x 1 pixel) is
never specified.
</p>
<p>
A trace captured with
<a href="https://github.com/apitrace/apitrace" target="_main">API trace</a>
shows this sequences of calls like this:
<pre>
2504 glBindTexture(target = GL_TEXTURE_2D, texture = 55)
2505 glTexImage2D(target = GL_TEXTURE_2D, level = 0, internalformat = GL_RGBA, width = 512, height = 512, border = 0, format = GL_RGB, type = GL_UNSIGNED_SHORT, pixels = blob(1572864))
2506 glTexImage2D(target = GL_TEXTURE_2D, level = 1, internalformat = GL_RGBA, width = 256, height = 256, border = 0, format = GL_RGB, type = GL_UNSIGNED_SHORT, pixels = blob(393216))
2507 glTexImage2D(target = GL_TEXTURE_2D, level = 2, internalformat = GL_RGBA, width = 128, height = 128, border = 0, format = GL_RGB, type = GL_UNSIGNED_SHORT, pixels = blob(98304))
[...]
2512 glTexImage2D(target = GL_TEXTURE_2D, level = 7, internalformat = GL_RGBA, width = 4, height = 4, border = 0, format = GL_RGB, type = GL_UNSIGNED_SHORT, pixels = blob(96))
2513 glTexImage2D(target = GL_TEXTURE_2D, level = 8, internalformat = GL_RGBA, width = 2, height = 2, border = 0, format = GL_RGB, type = GL_UNSIGNED_SHORT, pixels = blob(24))
2514 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MIN_FILTER, param = GL_LINEAR_MIPMAP_LINEAR)
2515 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_S, param = GL_REPEAT)
2516 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_T, param = GL_REPEAT)
2517 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MAG_FILTER, param = GL_NEAREST)
</pre>
<p>
Note that one would expect call 2514 to be glTexImage(level=9, width=1,
height=1) but it's not there.
</p>
<p>
The minification filter is GL_LINEAR_MIPMAP_LINEAR and the texture's
GL_TEXTURE_MAX_LEVEL is 1000 (the default) so a full mipmap is expected.
</p>
<p>
Later, these incomplete textures are bound before drawing calls.
According to the GL specification, if a fragment program or fragment shader
is being used, the sampler should return (0,0,0,1) ("black") when sampling
from an incomplete texture.
This is what Mesa does and the resulting rendering is darker than it should
be.
</p>
<p>
It appears that NVIDIA's driver (and possibly AMD's driver) detects this case
and returns (1,1,1,1) (white) which causes the rendering to appear brighter
and match the reference image (however, AMD's rendering is <em>much</em>
brighter than NVIDIA's).
</p>
<p>
If the fallback texture created in _mesa_get_fallback_texture() is
initialized to be full white instead of full black the rendering appears
correct.
However, we have no plans to implement this work-around in Mesa.
</p>
</BODY>
</HTML>
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