docs/viewperf.html

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   3 <TITLE>Viewperf Issues</TITLE>
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   9 <h1>Viewperf Issues</h1>
  10
  11 <p>
  12 This page lists known issues with
  13 <a href="http://www.spec.org/gwpg/gpc.static/vp11info.html" target="_main">SPEC Viewperf 11</a>
  14 when running on Mesa-based drivers.
  15 </p>
  16
  17 <p>
  18 The Viewperf data sets are basically GL API traces that are recorded from
  19 CAD applications, then replayed in the Viewperf framework.
  20 </p>
  21
  22 <p>
  23 The primary problem with these traces is they blindly use features and
  24 OpenGL extensions that were supported by the OpenGL driver when the trace
  25 was recorded,
  26 but there's no checks to see if those features are supported by the driver
  27 when playing back the traces with Viewperf.
  28 </p>
  29
  30 <p>
  31 These issues have been reported to the SPEC organization in the hope that
  32 they'll be fixed in the future.
  33 </p>
  34
  35
  36
  37 <h2>Catia-03 tests 3, 4, 8</h2>
  38
  39 <p>
  40 These tests use features of the
  41 <a href="http://www.opengl.org/registry/specs/NV/fragment_program2.txt"
  42 target="_main">
  43 GL_NV_fragment_program2</a> and
  44 <a href="http://www.opengl.org/registry/specs/NV/vertex_program3.txt"
  45 target="_main">
  46 GL_NV_vertex_program3</a> extensions without checking if the driver supports
  47 them.
  48 </p>
  49 <p>
  50 When Mesa tries to compile the vertex/fragment programs it generates errors
  51 (which Viewperf ignores).
  52 Subsequent drawing calls become no-ops and the rendering is incorrect.
  53 </p>
  54
  55
  56
  57 <h2>sw-02 tests 1, 2, 4</h2>
  58
  59 <p>
  60 These tests depend on the
  61 <a href="http://www.opengl.org/registry/specs/NV/primitive_restart.txt"
  62 target="_main">GL_NV_primitive_restart</a> extension.
  63 </p>
  64
  65 <p>
  66 If the Mesa driver doesn't support this extension the rendering will
  67 be incorrect and the test will fail.
  68 </p>
  69
  70
  71 <h2>Lightwave-01 test 3</h2>
  72
  73 <p>
  74 This test uses a number of mipmapped textures, but the textures are
  75 incomplete because the last/smallest mipmap level (1 x 1 pixel) is
  76 never specified.
  77 </p>
  78
  79 <p>
  80 A trace captured with
  81 <a href="https://github.com/apitrace/apitrace" target="_main">API trace</a>
  82 shows this sequences of calls like this:
  83
  84 <pre>
  85 2504 glBindTexture(target = GL_TEXTURE_2D, texture = 55)
  86 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))
  87 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))
  88 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))
  89 [...]
  90 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))
  91 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))
  92 2514 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MIN_FILTER, param = GL_LINEAR_MIPMAP_LINEAR)
  93 2515 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_S, param = GL_REPEAT)
  94 2516 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_T, param = GL_REPEAT)
  95 2517 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MAG_FILTER, param = GL_NEAREST)
  96 </pre>
  97
  98 <p>
  99 Note that one would expect call 2514 to be glTexImage(level=9, width=1,
 100 height=1) but it's not there.
 101 </p>
 102
 103 <p>
 104 The minification filter is GL_LINEAR_MIPMAP_LINEAR and the texture's
 105 GL_TEXTURE_MAX_LEVEL is 1000 (the default) so a full mipmap is expected.
 106 </p>
 107
 108 <p>
 109 Later, these incomplete textures are bound before drawing calls.
 110 According to the GL specification, if a fragment program or fragment shader
 111 is being used, the sampler should return (0,0,0,1) ("black") when sampling
 112 from an incomplete texture.
 113 This is what Mesa does and the resulting rendering is darker than it should
 114 be.
 115 </p>
 116
 117 <p>
 118 It appears that NVIDIA's driver (and possibly AMD's driver) detects this case
 119 and returns (1,1,1,1) (white) which causes the rendering to appear brighter
 120 and match the reference image (however, AMD's rendering is <em>much</em>
 121 brighter than NVIDIA's).
 122 </p>
 123
 124 <p>
 125 If the fallback texture created in _mesa_get_fallback_texture() is
 126 initialized to be full white instead of full black the rendering appears
 127 correct.
 128 However, we have no plans to implement this work-around in Mesa.
 129
 130 </p>
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