NAMEglAlphaFunc -- specify the alpha test function
void glAlphaFunc(GLenum func
- Specifies the alpha comparison function. Symbolic constants
GL_NEVER, GL_LESS, GL_EQUAL,
GL_LEQUAL, GL_GREATER, GL_NOTEQUAL,
GL_GEQUAL and GL_ALWAYS are accepted. The
default function is GL_ALWAYS.
- Specifies the reference value that incoming alpha values
are compared to. This value is clamped to the range 0 through
1, where 0 represents the lowest possible value and 1 the
highest possible value. The default reference is 0.
The alpha test discards fragments depending on the outcome of a comparison
between the incoming fragment's alpha value and a constant reference value.
glAlphaFunc specifies the reference and comparison function. The
comparison is performed only if alpha testing is enabled. (See
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 comparison passes, the incoming fragment is
drawn, conditional on subsequent stencil and depth buffer tests. If the
comparison fails, no change is made to the frame buffer at that pixel location.
The comparison functions are as follows:
glAlphaFunc operates on all pixel writes, 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
Passes if the incoming alpha value is less than the reference value.
Passes if the incoming alpha value is equal to the reference value.
Passes if the incoming alpha value is less than or equal to the
Passes if the incoming alpha value is greater than the
Passes if the incoming alpha value is not equal to the
Passes if the incoming alpha value is greater than or equal to the
Alpha testing is done only in RGBA mode.
GL_INVALID_ENUM is generated if func is not an accepted value.
GL_INVALID_OPERATION is generated if glAlphaFunc is called
between a call to glBegin and the
corresponding call to glEnd.
glGet with argument
glGet with argument
glIsEnabled with argument
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© 1995 Uwe Behrens. All rights reserved.