gl.AlphaFunc(func, ref)
gl.AlphaFunc()
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 gl.Enable() and gl.Disable() 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:
#GL_NEVER
#GL_LESS
#GL_EQUAL
#GL_LEQUAL
#GL_GREATER
#GL_NOTEQUAL
#GL_GEQUAL
#GL_ALWAYS
gl.AlphaFunc()
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. gl.AlphaFunc()
does not affect
screen clear operations.
Please consult an OpenGL reference manual for more information.
#GL_INVALID_ENUM
is generated if func
is not an accepted value.
#GL_INVALID_OPERATION
is generated if gl.AlphaFunc()
is executed between the execution of gl.Begin() and the corresponding execution of gl.End().
#GL_ALPHA_TEST_FUNC
gl.Get() with argument #GL_ALPHA_TEST_REF
gl.IsEnabled() with argument #GL_ALPHA_TEST