| '''OpenGL extension EXT.depth_bounds_test |
| |
| This module customises the behaviour of the |
| OpenGL.raw.GL.EXT.depth_bounds_test to provide a more |
| Python-friendly API |
| |
| 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: |
| http://www.opengl.org/registry/specs/EXT/depth_bounds_test.txt |
| ''' |
| from OpenGL import platform, constant, arrays |
| from OpenGL import extensions, wrapper |
| import ctypes |
| from OpenGL.raw.GL import _types, _glgets |
| from OpenGL.raw.GL.EXT.depth_bounds_test import * |
| from OpenGL.raw.GL.EXT.depth_bounds_test import _EXTENSION_NAME |
|
|
| def glInitDepthBoundsTestEXT(): |
| '''Return boolean indicating whether this extension is available''' |
| from OpenGL import extensions |
| return extensions.hasGLExtension( _EXTENSION_NAME ) |
|
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|
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| |
