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'''OpenGL extension SUN.global_alpha |
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This module customises the behaviour of the |
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OpenGL.raw.GL.SUN.global_alpha to provide a more |
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Python-friendly API |
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Overview (from the spec) |
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Transparency is done in OpenGL using alpha blending. An alpha value |
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of 0.0 is used for fully transparent objects, while an alpha value |
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of 1.0 is used for fully opaque objects. A value of 0.25 is 75% |
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transparent, and so on. |
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OpenGL defines alpha as a component of the vertex color state. |
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Whenever a color is set, the alpha component is set along with the |
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red, green, and blue components. This means that transparency |
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can't be changed for primitives with per-vertex colors without |
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modifying the color of each vertex, replacing the old alpha |
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component with the new alpha component. This can be very expensive |
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for objects that are drawn using vertex arrays; it all but |
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precludes the use of display lists. |
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This extension defines a new global alpha attribute that can be |
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used to specify an alpha factor that is independent from the alpha |
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component of the color value. The global alpha factor is |
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multiplied by the fragment's alpha value after primitive |
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rasterization and prior to texture mapping, replacing the |
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fragment's alpha value. The global alpha extension is only |
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specified in RGBA mode and must be applied prior to any texture |
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mapping operation. It is enabled by a new GLOBAL_ALPHA flag. |
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The official definition of this extension is available here: |
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http://www.opengl.org/registry/specs/SUN/global_alpha.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.SUN.global_alpha import * |
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from OpenGL.raw.GL.SUN.global_alpha import _EXTENSION_NAME |
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def glInitGlobalAlphaSUN(): |
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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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