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View Full Version : What kind of values should gl_FragDepth be giving?



Leadwerks
05-24-2007, 11:10 AM
I would think this would return a float between 0 and 1, but it seems to always return 0. All I am trying to do is get the fragment depth for fog rendering.

Komat
05-24-2007, 12:39 PM
The gl_FragDepth is output variable which is used to override depth of the fragment. The fragment depth calculated by hw is stored within gl_FragCoord.z

Leadwerks
05-24-2007, 12:42 PM
I thought ATI didn't support gl_FragCoord.z.

Komat
05-24-2007, 01:07 PM
Originally posted by Leadwerks:
I thought ATI didn't support gl_FragCoord.z. It does not have explicit hw support however the driver tries to emulate it using ordinary varying. It is possible that use of additional feature such as polygon offset (
see here (http://www.opengl.org/discussion_boards/ubb/ultimatebb.php?ubb=get_topic;f=11;t=001243#000000) ) will force it to sw emulation or that some drivers have buggy implementation.

If you do not wish to rely on the driver, you can calculate the depth in vertex shader and send it trough the varying manually.

Leadwerks
05-24-2007, 02:22 PM
Thank you.