OpenGL extension EXT.depth_bounds_test
This module customises the behaviour of the
OpenGL.raw.GL.EXT.depth_bounds_test to provide a more
Overview (from the spec)
This extension adds a new per-fragment test that is, logically,
after the scissor test and before the alpha test. The depth bounds
test compares the depth value stored at the location given by the
incoming fragment's (xw,yw) coordinates to a user-defined minimum
and maximum depth value. If the stored depth value is outside the
user-defined range (exclusive), the incoming fragment is discarded.
Unlike the depth test, the depth bounds test has NO dependency on
the fragment's window-space depth value.
This functionality is useful in the context of attenuated stenciled
shadow volume rendering. To motivate the functionality's utility
in this context, we first describe how conventional scissor testing
can be used to optimize shadow volume rendering.
If an attenuated light source's illumination can be bounded to a
rectangle in XY window-space, the conventional scissor test can be
used to discard shadow volume fragments that are guaranteed to be
outside the light source's window-space XY rectangle. The stencil
increments and decrements that would otherwise be generated by these
scissored fragments are inconsequential because the light source's
illumination can pre-determined to be fully attenuated outside the
scissored region. In other words, the scissor test can be used to
discard shadow volume fragments rendered outside the scissor, thereby
improving performance, without affecting the ultimate illumination
of these pixels with respect to the attenuated light source.
This scissoring optimization can be used both when rendering
the stenciled shadow volumes to update stencil (incrementing and
decrementing the stencil buffer) AND when adding the illumination
contribution of attenuated light source's.
In a similar fashion, we can compute the attenuated light source's
window-space Z bounds (zmin,zmax) of consequential illumination.
Unless a depth value (in the depth buffer) at a pixel is within
the range [zmin,zmax], the light source's illumination can be
pre-determined to be inconsequential for the pixel. Said another
way, the pixel being illuminated is either far enough in front of
or behind the attenuated light source so that the light source's
illumination for the pixel is fully attenuated. The depth bounds
test can perform this test.
The official definition of this extension is available here:
|EXTENSION_NAME = 'GL_EXT_depth_bounds_test'|
GL_DEPTH_BOUNDS_EXT = GL_DEPTH_BOUNDS_EXT
GL_DEPTH_BOUNDS_TEST_EXT = GL_DEPTH_BOUNDS_TEST_EXT
__file__ = '/home/mcfletch/pylive/OpenGL/GL/EXT/depth_bounds_test.pyc'
__name__ = 'OpenGL.GL.EXT.depth_bounds_test'
__package__ = 'OpenGL.GL.EXT'
glDepthBoundsEXT = <OpenGL.platform.baseplatform.glDepthBoundsEXT object at 0x7560590>