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'''OpenGL extension AMD.interleaved_elements |
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This module customises the behaviour of the |
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OpenGL.raw.GL.AMD.interleaved_elements to provide a more |
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Python-friendly API |
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Overview (from the spec) |
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The glDrawElements function and its variants (instanced and indirect, |
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for example) allow OpenGL to draw indexed arrays of vertices. Since its |
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inception, OpenGL has supported unsigned bytes, unsigned shorts and |
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unsigned integers as index types. However, all enabled vertex arrays may |
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be represented by at most one shared index. |
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A common scenario in graphics rendering is that several faces share |
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a vertex where, for each face some properties of a vertex (position and |
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texture coordinates, for example) should be common but others must be |
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unique (colors, normals, and so on). Consider a mesh of a cube with |
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per-face normals, for example. There are 8 vertices and 6 normals, and 12 |
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triangles (where each face of the cube is represented as two triangles). |
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To render this cube, we must compute the 24 unique permutations of |
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position and normal and build a new element list to index into it. In |
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fact, any advantage of indexed draw is lost here as the number of required |
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permutations is equal to the final vertex count required to draw the |
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object. |
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This extension allows OpenGL to process multi-component packed element |
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data. The maximum size of a vertex's index data is not increased, but the |
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facility to store 2 16-bit or 2 or 4 8-bit indices per vertex is introduced. |
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Each vertex attribute is given a swizzle property to allow its index to |
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be sourced from one of up to 4 channels of index data. This effectively |
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allows an application to supply multiple interleaved streams of index data |
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to OpenGL. Each vertex attribute is given a 'channel selector' to select |
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one of the up to 4 channels of vertex index information presented to |
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OpenGL. This enables the use-case described above and many more. |
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The swizzle parameter is also applied to vertex indices passed to shaders, |
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and updates to the definition of base vertex parameters and primitive |
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restart are applied. |
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The official definition of this extension is available here: |
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http://www.opengl.org/registry/specs/AMD/interleaved_elements.txt |
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''' |
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from OpenGL import platform, constant, arrays |
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from OpenGL import extensions, wrapper |
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import ctypes |
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from OpenGL.raw.GL import _types, _glgets |
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from OpenGL.raw.GL.AMD.interleaved_elements import * |
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from OpenGL.raw.GL.AMD.interleaved_elements import _EXTENSION_NAME |
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def glInitInterleavedElementsAMD(): |
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'''Return boolean indicating whether this extension is available''' |
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from OpenGL import extensions |
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return extensions.hasGLExtension( _EXTENSION_NAME ) |
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