| | '''OpenGL extension NV.occlusion_query |
| | |
| | This module customises the behaviour of the |
| | OpenGL.raw.GL.NV.occlusion_query to provide a more |
| | Python-friendly API |
| | |
| | Overview (from the spec) |
| | |
| | The HP_occlusion_test extension defines a mechanism whereby an |
| | application can query the visibility of an object, where "visible" |
| | means that at least one pixel passes the depth and stencil tests. |
| | |
| | The HP extension has two major shortcomings. |
| | |
| | - It returns the result as a simple GL_TRUE/GL_FALSE result, when in |
| | fact it is often useful to know exactly how many pixels passed. |
| | - It provides only a simple "stop-and-wait" model for using multiple |
| | queries. The application begins an occlusion test and ends it; |
| | then, at some later point, it asks for the result, at which point |
| | the driver must stop and wait until the result from the previous |
| | test is back before the application can even begin the next one. |
| | This is a very simple model, but its performance is mediocre when |
| | an application wishes to perform many queries, and it eliminates |
| | most of the opportunites for parallelism between the CPU and GPU. |
| | |
| | This extension solves both of those problems. It returns as its |
| | result the number of pixels that pass, and it provides an interface |
| | conceptually similar to that of NV_fence that allows applications to |
| | issue many occlusion queries before asking for the result of any one. |
| | As a result, they can overlap the time it takes for the occlusion |
| | query results to be returned with other, more useful work, such as |
| | rendering other parts of the scene or performing other computations |
| | on the CPU. |
| | |
| | There are many situations where a pixel count, rather than a boolean |
| | result, is useful. |
| | |
| | - If the visibility test is an object bounding box being used to |
| | decide whether to skip the object, sometimes it can be acceptable, |
| | and beneficial to performance, to skip an object if less than some |
| | threshold number of pixels could be visible. |
| | - Knowing the number of pixels visible in the bounding box may also |
| | help decide what level of detail a model should be drawn with. If |
| | only a few pixels are visible, a low-detail model may be |
| | acceptable. In general, this allows level-of-detail mechanisms to |
| | be slightly less ad hoc. |
| | - "Depth peeling" techniques, such as order-independent transparency, |
| | would typically like to know when to stop rendering more layers; it |
| | is difficult to come up with a way to determine a priori how many |
| | layers to use. A boolean count allows applications to stop when |
| | more layers will not affect the image at all, but this will likely |
| | be unacceptable for performance, with minimal gains to image |
| | quality. Instead, it makes more sense to stop rendering when the |
| | number of pixels goes below a threshold; this should provide better |
| | results than any of these other algorithms. |
| | - Occlusion queries can be used as a replacement for glReadPixels of |
| | the depth buffer to determine whether, say, a light source is |
| | visible for the purposes of a lens flare effect or a halo to |
| | simulate glare. Pixel counts allow you to compute the percentage |
| | of the light source that is visible, and the brightness of these |
| | effects can be modulated accordingly. |
| | |
| | The official definition of this extension is available here: |
| | http://www.opengl.org/registry/specs/NV/occlusion_query.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.NV.occlusion_query import * |
| | from OpenGL.raw.GL.NV.occlusion_query import _EXTENSION_NAME |
| |
|
| | def glInitOcclusionQueryNV(): |
| | '''Return boolean indicating whether this extension is available''' |
| | from OpenGL import extensions |
| | return extensions.hasGLExtension( _EXTENSION_NAME ) |
| |
|
| | glGenOcclusionQueriesNV=wrapper.wrapper(glGenOcclusionQueriesNV).setOutput( |
| | 'ids',size=lambda x:(x,),pnameArg='n',orPassIn=True |
| | ) |
| | |
| | glDeleteOcclusionQueriesNV=wrapper.wrapper(glDeleteOcclusionQueriesNV).setInputArraySize( |
| | 'ids', None |
| | ) |
| | glGetOcclusionQueryivNV=wrapper.wrapper(glGetOcclusionQueryivNV).setOutput( |
| | 'params',size=_glgets._glget_size_mapping,pnameArg='pname',orPassIn=True |
| | ) |
| | glGetOcclusionQueryuivNV=wrapper.wrapper(glGetOcclusionQueryuivNV).setOutput( |
| | 'params',size=_glgets._glget_size_mapping,pnameArg='pname',orPassIn=True |
| | ) |
| | |
