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NAMEglAlphaFunc - specify the alpha test functionC SPECIFICATIONvoid glAlphaFunc( GLenum func,GLclampf ref ) PARAMETERS
DESCRIPTIONThe alpha test discards fragments depending on the outcome of a comparison between an incoming fragment's alpha value and a constant reference value. glAlphaFunc specifies the reference value and the comparison function. The comparison is performed only if alpha testing is enabled. By default, it is not enabled. (See glEnable and glDisable of GL_ALPHA_TEST.)func and ref specify the conditions under which the pixel is drawn. The incoming alpha value is compared to ref using the function specified by func. If the value passes the comparison, the incoming fragment is drawn if it also passes subsequent stencil and depth buffer tests. If the value fails the comparison, no change is made to the frame buffer at that pixel location. The comparison functions are as follows:
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. NOTESAlpha testing is performed only in RGBA mode.ERRORSGL_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. ASSOCIATED GETSglGet with argument GL_ALPHA_TEST_FUNCglGet with argument GL_ALPHA_TEST_REF glIsEnabled with argument GL_ALPHA_TEST SEE ALSOglBlendFunc, glClear, glDepthFunc, glEnable, glStencilFunc Visit the GSP FreeBSD Man Page Interface. |