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authormarha <marha@users.sourceforge.net>2013-03-11 09:17:45 +0100
committermarha <marha@users.sourceforge.net>2013-03-11 09:17:45 +0100
commit514e0809a42027e2178bf0eccd526a08da60f399 (patch)
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fontconfig libX11 mesa pixman xserver xkeyboard-config git update 11 Mar
2013 xserver commit 5047810a4c20fab444b8c6eb146c55dcdb0d4219 xkeyboard-config commit 2ed85c1e936f7cd4a9540ace5c12b9fec60ee1fb libX11 commit 3996543c1b2919e97d61a5d70fe1ebd7cd76fc83 pixman commit aaae3d8eefa069098e9014822817ca1429fdea46 fontconfig commit bdf1581e3de5528f397f19bfd4ca9caaf9e7fe4a mesa commit b21a9d46e4be0c666327569f07b9cddeb4d42d38
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@@ -203,6 +203,35 @@ This causes the object in question to be drawn in a strange orientation
and with a semi-random color (between white and black) since GL_FOG is enabled.
</p>
+
+<h2>Proe-05 test 1</h2>
+
+<p>
+This uses depth testing but there's two problems:
+<ol>
+<li>The glXChooseFBConfig() call doesn't request a depth buffer
+<li>The test never calls glClear(GL_DEPTH_BUFFER_BIT) to initialize the depth buffer
+</ol>
+<p>
+If the chosen visual does not have a depth buffer, you'll see the wireframe
+car model but it won't be rendered correctly.
+</p>
+If (by luck) the chosen visual has a depth buffer, its initial contents
+will be undefined so you may or may not see parts of the model.
+<p>
+Interestingly, with NVIDIA's driver most visuals happen to have a depth buffer
+and apparently the contents are initialized to 1.0 by default so this test
+just happens to work with their drivers.
+</p>
+
+<p>
+Finally, even if a depth buffer was requested and the glClear(GL_COLOR_BUFFER_BIT)
+calls were changed to glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
+the problem still wouldn't be fixed because GL_DEPTH_WRITEMASK=GL_FALSE when
+glClear is called so clearing the depth buffer would be a no-op anyway.
+</p>
+
+
</div>
</body>
</html>