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268 lines
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HTML
268 lines
8.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html lang="en">
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<head>
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<meta http-equiv="content-type" content="text/html; charset=utf-8">
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<title>Viewperf Issues</title>
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<link rel="stylesheet" type="text/css" href="mesa.css">
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</head>
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<body>
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<div class="header">
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<h1>The Mesa 3D Graphics Library</h1>
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</div>
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<iframe src="contents.html"></iframe>
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<div class="content">
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<h1>Viewperf Issues</h1>
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<p>
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This page lists known issues with
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<a href="http://www.spec.org/gwpg/gpc.static/vp11info.html" target="_main">SPEC Viewperf 11</a>
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when running on Mesa-based drivers.
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</p>
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<p>
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The Viewperf data sets are basically GL API traces that are recorded from
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CAD applications, then replayed in the Viewperf framework.
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</p>
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<p>
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The primary problem with these traces is they blindly use features and
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OpenGL extensions that were supported by the OpenGL driver when the trace
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was recorded,
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but there's no checks to see if those features are supported by the driver
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when playing back the traces with Viewperf.
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</p>
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<p>
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These issues have been reported to the SPEC organization in the hope that
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they'll be fixed in the future.
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</p>
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<p>
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Some of the Viewperf tests use a lot of memory.
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At least 2GB of RAM is recommended.
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</p>
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<h2>Catia-03 test 2</h2>
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<p>
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This test creates over 38000 vertex buffer objects. On some systems
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this can exceed the maximum number of buffer allocations. Mesa
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generates GL_OUT_OF_MEMORY errors in this situation, but Viewperf
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does no error checking and continues. When this happens, some drawing
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commands become no-ops. This can also eventually lead to a segfault
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either in Viewperf or the Mesa driver.
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</p>
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<h2>Catia-03 tests 3, 4, 8</h2>
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<p>
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These tests use features of the
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<a href="http://www.opengl.org/registry/specs/NV/fragment_program2.txt"
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target="_main">
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GL_NV_fragment_program2</a> and
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<a href="http://www.opengl.org/registry/specs/NV/vertex_program3.txt"
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target="_main">
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GL_NV_vertex_program3</a> extensions without checking if the driver supports
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them.
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</p>
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<p>
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When Mesa tries to compile the vertex/fragment programs it generates errors
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(which Viewperf ignores).
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Subsequent drawing calls become no-ops and the rendering is incorrect.
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</p>
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<h2>sw-02 tests 1, 2, 4, 6</h2>
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<p>
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These tests depend on the
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<a href="http://www.opengl.org/registry/specs/NV/primitive_restart.txt"
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target="_main">GL_NV_primitive_restart</a> extension.
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</p>
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<p>
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If the Mesa driver doesn't support this extension the rendering will
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be incorrect and the test will fail.
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</p>
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<p>
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Also, the color of the line drawings in test 2 seem to appear in a random
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color. This is probably due to some uninitialized state somewhere.
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</p>
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<h2>sw-02 test 6</h2>
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<p>
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The lines drawn in this test appear in a random color.
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That's because texture mapping is enabled when the lines are drawn, but no
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texture image is defined (glTexImage2D() is called with pixels=NULL).
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Since GL says the contents of the texture image are undefined in that
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situation, we get a random color.
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</p>
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<h2>Lightwave-01 test 3</h2>
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<p>
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This test uses a number of mipmapped textures, but the textures are
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incomplete because the last/smallest mipmap level (1 x 1 pixel) is
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never specified.
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</p>
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<p>
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A trace captured with
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<a href="https://github.com/apitrace/apitrace" target="_main">API trace</a>
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shows this sequences of calls like this:
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<pre>
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2504 glBindTexture(target = GL_TEXTURE_2D, texture = 55)
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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))
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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))
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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))
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[...]
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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))
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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))
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2514 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MIN_FILTER, param = GL_LINEAR_MIPMAP_LINEAR)
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2515 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_S, param = GL_REPEAT)
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2516 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_T, param = GL_REPEAT)
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2517 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MAG_FILTER, param = GL_NEAREST)
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</pre>
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<p>
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Note that one would expect call 2514 to be glTexImage(level=9, width=1,
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height=1) but it's not there.
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</p>
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<p>
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The minification filter is GL_LINEAR_MIPMAP_LINEAR and the texture's
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GL_TEXTURE_MAX_LEVEL is 1000 (the default) so a full mipmap is expected.
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</p>
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<p>
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Later, these incomplete textures are bound before drawing calls.
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According to the GL specification, if a fragment program or fragment shader
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is being used, the sampler should return (0,0,0,1) ("black") when sampling
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from an incomplete texture.
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This is what Mesa does and the resulting rendering is darker than it should
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be.
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</p>
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<p>
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It appears that NVIDIA's driver (and possibly AMD's driver) detects this case
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and returns (1,1,1,1) (white) which causes the rendering to appear brighter
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and match the reference image (however, AMD's rendering is <em>much</em>
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brighter than NVIDIA's).
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</p>
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<p>
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If the fallback texture created in _mesa_get_fallback_texture() is
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initialized to be full white instead of full black the rendering appears
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correct.
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However, we have no plans to implement this work-around in Mesa.
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</p>
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<h2>Maya-03 test 2</h2>
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<p>
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This test makes some unusual calls to glRotate. For example:
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</p>
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<pre>
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glRotate(50, 50, 50, 1);
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glRotate(100, 100, 100, 1);
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glRotate(52, 52, 52, 1);
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</pre>
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<p>
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These unusual values lead to invalid modelview matrices.
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For example, the last glRotate command above produces this matrix with Mesa:
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<pre>
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1.08536e+24 2.55321e-23 -0.000160389 0
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5.96937e-25 1.08536e+24 103408 0
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103408 -0.000160389 1.74755e+09 0
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0 0 0 nan
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</pre>
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and with NVIDIA's OpenGL:
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<pre>
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1.4013e-45 0 -nan 0
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0 1.4013e-45 1.4013e-45 0
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1.4013e-45 -nan 1.4013e-45 0
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0 0 0 1.4013e-45
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</pre>
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<p>
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This causes the object in question to be drawn in a strange orientation
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and with a semi-random color (between white and black) since GL_FOG is enabled.
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</p>
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<h2>Proe-05 test 1</h2>
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<p>
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This uses depth testing but there's two problems:
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<ol>
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<li>The glXChooseFBConfig() call doesn't request a depth buffer
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<li>The test never calls glClear(GL_DEPTH_BUFFER_BIT) to initialize the depth buffer
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</ol>
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<p>
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If the chosen visual does not have a depth buffer, you'll see the wireframe
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car model but it won't be rendered correctly.
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</p>
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If (by luck) the chosen visual has a depth buffer, its initial contents
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will be undefined so you may or may not see parts of the model.
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<p>
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Interestingly, with NVIDIA's driver most visuals happen to have a depth buffer
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and apparently the contents are initialized to 1.0 by default so this test
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just happens to work with their drivers.
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</p>
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<p>
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Finally, even if a depth buffer was requested and the glClear(GL_COLOR_BUFFER_BIT)
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calls were changed to glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
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the problem still wouldn't be fixed because GL_DEPTH_WRITEMASK=GL_FALSE when
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glClear is called so clearing the depth buffer would be a no-op anyway.
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</p>
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<h2>Proe-05 test 6</h2>
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<p>
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This test draws an engine model with a two-pass algorithm.
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The first pass is drawn with polygon stipple enabled.
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The second pass is drawn without polygon stipple but with blending
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and GL_DEPTH_FUNC=GL_LEQUAL.
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If either of the two passes happen to use a software fallback of some
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sort, the Z values of fragments may be different between the two passes.
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This leads to incorrect rendering.
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</p>
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<p>
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For example, the VMware SVGA gallium driver uses a special semi-fallback path
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for drawing with polygon stipple.
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Since the two passes are rendered with different vertex transformation
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implementations, the rendering doesn't appear as expected.
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Setting the SVGA_FORCE_SWTNL environment variable to 1 will force the
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driver to use the software vertex path all the time and clears up this issue.
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</p>
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<p>
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According to the OpenGL invariance rules, there's no guarantee that
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the pixels produced by these two rendering states will match.
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To achieve invariance, both passes should enable polygon stipple and
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blending with appropriate patterns/modes to ensure the same fragments
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are produced in both passes.
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</p>
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</div>
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</body>
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</html>
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