gl_occlusion_test_hp man page on SunOS

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GL_OCCLUSION_TEST_HP(3gl)			     GL_OCCLUSION_TEST_HP(3gl)

NAME
       GL_OCCLUSION_TEST_HP  -	allows an application to quickly determine the
       visibility of some set of geometry based on the visbility of the bound‐
       ing box of the geometry.

DESCRIPTION
       Enabling	 GL_OCCLUSION_TEST_HP allows an application to render a bound‐
       ing box of some complicated geometry and at the completion of the  ren‐
       dering  to  determine  if  any  of the geometry could or did modify the
       depth buffer.  If the occlusion test failed, ie the  bounding  box  was
       depth  culled due to the current contents of the depth buffer, then the
       geometry enclosed by the bounding box would also be depth culled. Based
       on  the	occlusion test result, an application can choose to not render
       the complicated geometry when its bounding box is depth	culled;	 hence
       the rendering performance can be significantly improved.

       Occlusion culling operates independently of the current rendering state
       (ie. when occlusion culling is enabled fragments are generated and  the
       depth  and/or  color  buffer  may  be updated). To prevent updating the
       depth/color buffers, the application must disable updates to these buf‐
       fers.  As  a  side effect of reading the occlusion result, the internal
       result state is cleared.

       The expected usage of this feature is :

	   - disable updates to color and depth buffer (optional)
	       glDepthMask(GL_FALSE)
	       glColorMask(GL_FALSE,GL_FALSE,GL_FALSE,GL_FALSE)
	   - enable occlusion test
	       glEnable(GL_OCCLUSION_TEST_HP)
	   - render bounding geometry
	       gl rendering calls
	   - disable occlusion test
	       glDisable(GL_OCCLUSION_TEST_HP)
	   - enable updates to color and depth buffer
	       glDepthMask(GL_TRUE)
	       glColorMask(GL_TRUE,GL_TRUE,GL_TRUE,GL_TRUE)
	   - read occlusion test result
	       glGetBooleanv(GL_OCCLUSION_RESULT_HP, &result)
	   - if (result) render internal geometry
	     else don't render

       For this extension to be useful, the time to render the geometry	 under
       test  should  be	 much  more  than rendering the encompassing geometry,
       including reading back the test result.

       GL_OCCLUSION_TEST_HP can be specified in	 the <cap> parameter of	 glEn‐
       able, glDisable, and glIsEnabled.

       GL_OCCLUSION_RESULT_HP  can  be	specified  in the <pname> parameter of
       glGetBooleanv, glGetIntegerv, glGetFloatv, and glGetDoublev.

SEE ALSO
       glEnable, glDisable, glIsEnabled, glGetBooleanv, glGetIntegerv,	glGet‐
       Floatv, and glGetDoublev.

				   10 Apr 98	     GL_OCCLUSION_TEST_HP(3gl)
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