[info-performer] depth buffer write is slow.

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From: Performer Newsgroup (csklu_pf++at++yahoo.com)
Date: 08/14/2002 06:37:20

Performers,

Again maybe another OpenGL question: I'm writing
values to the depth buffer directly using:

glDrawPixels( width,height, GL_DEPTH_COMPONENT,
GL_FLOAT, depths).

This is much slower than the corresponding write using
GL_RGBA and GL_UNSIGNED_INT (with depths converted to
rgba values). Performer reports that the depth buffer
size is 24 (on a GeForce3, RedHat 7.3). Could this
slowness be because sizeof(GL_FLOAT) !=
depthbuffersize/8? Would it make any difference if I
use a depth buffer depth of 16 and GL_UNSIGNED_SHORTs?
Any other suggestions/explanations?

Thanks,
Chris

code looks like:

glPushAttrib(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE );
glDepthMask(GL_TRUE);
glDepthFunc(GL_ALWAYS);
glDrawPixels(w,h,GL_DEPTH_COMPONENT,GL_FLOAT,depths);
glPopAttrib();

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