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diff --git a/docs/viewperf.html b/docs/viewperf.html index ab2fd67ef60..3bbe1978ab8 100644 --- a/docs/viewperf.html +++ b/docs/viewperf.html @@ -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> |