HP b2600 Reference Manual page 14

A
glAlphaFunc
glAlphaFunc operates on all pixel write operations, including those resulting from the
scan conversion of points, lines, polygons, and bitmaps, and from pixel draw and copy
operations. glAlphaFunc does not affect screen-clear operations.
Notes
Alpha testing is performed only in RGBA mode.
Errors
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•
Associated Gets
glGet with argument GL_ALPHA_TEST_FUNC
glGet with argument GL_ALPHA_TEST_REF
glIsEnabled with argument GL_ALPHA_TEST
See Also
glBlendFunc,
glClear,
glDepthFunc,
glEnable,
glStencilFunc
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GL_INVALID_ENUM is generated if func is not an accepted value.
GL_INVALID_OPERATION is generated if glAlphaFunc is executed between the
execution of glBegin and the corresponding execution of glEnd.
Chapter 1