docs/viewperf.html

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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 test 2</h2>
  38
  39 <p>
  40 This test creates over 38000 vertex buffer objects.  On some systems
  41 this can exceed the maximum number of buffer allocations.  Mesa
  42 generates GL_OUT_OF_MEMORY errors in this situation, but Viewperf
  43 does no error checking and continues.  When this happens, some drawing
  44 commands become no-ops.  This can also eventually lead to a segfault
  45 either in Viewperf or the Mesa driver.
  46 </p>
  47
  48
  49
  50 <h2>Catia-03 tests 3, 4, 8</h2>
  51
  52 <p>
  53 These tests use features of the
  54 <a href="http://www.opengl.org/registry/specs/NV/fragment_program2.txt"
  55 target="_main">
  56 GL_NV_fragment_program2</a> and
  57 <a href="http://www.opengl.org/registry/specs/NV/vertex_program3.txt"
  58 target="_main">
  59 GL_NV_vertex_program3</a> extensions without checking if the driver supports
  60 them.
  61 </p>
  62 <p>
  63 When Mesa tries to compile the vertex/fragment programs it generates errors
  64 (which Viewperf ignores).
  65 Subsequent drawing calls become no-ops and the rendering is incorrect.
  66 </p>
  67
  68
  69
  70 <h2>sw-02 tests 1, 2, 4, 6</h2>
  71
  72 <p>
  73 These tests depend on the
  74 <a href="http://www.opengl.org/registry/specs/NV/primitive_restart.txt"
  75 target="_main">GL_NV_primitive_restart</a> extension.
  76 </p>
  77
  78 <p>
  79 If the Mesa driver doesn't support this extension the rendering will
  80 be incorrect and the test will fail.
  81 </p>
  82
  83
  84
  85 <h2>sw-02 test 6</h2>
  86
  87 <p>
  88 The lines drawn in this test appear in a random color.
  89 That's because texture mapping is enabled when the lines are drawn, but no
  90 texture image is defined (glTexImage2D() is called with pixels=NULL).
  91 Since GL says the contents of the texture image are undefined in that
  92 situation, we get a random color.
  93 </p>
  94
  95
  96
  97 <h2>Lightwave-01 test 3</h2>
  98
  99 <p>
 100 This test uses a number of mipmapped textures, but the textures are
 101 incomplete because the last/smallest mipmap level (1 x 1 pixel) is
 102 never specified.
 103 </p>
 104
 105 <p>
 106 A trace captured with
 107 <a href="https://github.com/apitrace/apitrace" target="_main">API trace</a>
 108 shows this sequences of calls like this:
 109
 110 <pre>
 111 2504 glBindTexture(target = GL_TEXTURE_2D, texture = 55)
 112 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))
 113 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))
 114 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))
 115 [...]
 116 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))
 117 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))
 118 2514 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MIN_FILTER, param = GL_LINEAR_MIPMAP_LINEAR)
 119 2515 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_S, param = GL_REPEAT)
 120 2516 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_WRAP_T, param = GL_REPEAT)
 121 2517 glTexParameteri(target = GL_TEXTURE_2D, pname = GL_TEXTURE_MAG_FILTER, param = GL_NEAREST)
 122 </pre>
 123
 124 <p>
 125 Note that one would expect call 2514 to be glTexImage(level=9, width=1,
 126 height=1) but it's not there.
 127 </p>
 128
 129 <p>
 130 The minification filter is GL_LINEAR_MIPMAP_LINEAR and the texture's
 131 GL_TEXTURE_MAX_LEVEL is 1000 (the default) so a full mipmap is expected.
 132 </p>
 133
 134 <p>
 135 Later, these incomplete textures are bound before drawing calls.
 136 According to the GL specification, if a fragment program or fragment shader
 137 is being used, the sampler should return (0,0,0,1) ("black") when sampling
 138 from an incomplete texture.
 139 This is what Mesa does and the resulting rendering is darker than it should
 140 be.
 141 </p>
 142
 143 <p>
 144 It appears that NVIDIA's driver (and possibly AMD's driver) detects this case
 145 and returns (1,1,1,1) (white) which causes the rendering to appear brighter
 146 and match the reference image (however, AMD's rendering is <em>much</em>
 147 brighter than NVIDIA's).
 148 </p>
 149
 150 <p>
 151 If the fallback texture created in _mesa_get_fallback_texture() is
 152 initialized to be full white instead of full black the rendering appears
 153 correct.
 154 However, we have no plans to implement this work-around in Mesa.
 155 </p>
 156
 157
 158 <h2>Maya-03 test 2</h2>
 159
 160 <p>
 161 This test makes some unusual calls to glRotate.  For example:
 162 </p>
 163 <pre>
 164 glRotate(50, 50, 50, 1);
 165 glRotate(100, 100, 100, 1);
 166 glRotate(52, 52, 52, 1);
 167 </pre>
 168 <p>
 169 These unusual values lead to invalid modelview matrices.
 170 For example, the last glRotate command above produces this matrix with Mesa:
 171 <pre>
 172 1.08536e+24 2.55321e-23 -0.000160389 0
 173 5.96937e-25 1.08536e+24 103408 0
 174 103408 -0.000160389 1.74755e+09 0
 175 0 0 0 nan
 176 </pre>
 177 and with NVIDIA's OpenGL:
 178 <pre>
 179 1.4013e-45 0 -nan 0
 180 0 1.4013e-45 1.4013e-45 0
 181 1.4013e-45 -nan 1.4013e-45 0
 182 0 0 0 1.4013e-45
 183 </pre>
 184 <p>
 185 This causes the object in question to be drawn in a strange orientation
 186 and with a semi-random color (between white and black) since GL_FOG is enabled.
 187 </p>
 188
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