glalphafunc(3g) [centos man page]

GLALPHAFUNC(3G) 						   OpenGL Manual						   GLALPHAFUNC(3G)

NAME

       glAlphaFunc - specify the alpha test function

C SPECIFICATION

       void glAlphaFunc(GLenum func, GLclampf ref);

PARAMETERS

       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 initial value is GL_ALWAYS.

       ref
	   Specifies the reference value that incoming alpha values are compared to. This value is clamped to the range 0 1, where 0 represents
	   the lowest possible alpha value and 1 the highest possible value. The initial reference value is 0.

DESCRIPTION

       The 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:

       GL_NEVER
	   Never passes.

       GL_LESS
	   Passes if the incoming alpha value is less than the reference value.

       GL_EQUAL
	   Passes if the incoming alpha value is equal to the reference value.

       GL_LEQUAL
	   Passes if the incoming alpha value is less than or equal to the reference value.

       GL_GREATER
	   Passes if the incoming alpha value is greater than the reference value.

       GL_NOTEQUAL
	   Passes if the incoming alpha value is not equal to the reference value.

       GL_GEQUAL
	   Passes if the incoming alpha value is greater than or equal to the reference value.

       GL_ALWAYS
	   Always passes (initial value).

       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

       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().

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()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							   GLALPHAFUNC(3G)

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GLDEPTHFUNC(3G) 						   OpenGL Manual						   GLDEPTHFUNC(3G)

NAME

       glDepthFunc - specify the value used for depth buffer comparisons

C SPECIFICATION

       void glDepthFunc(GLenum func);

PARAMETERS

       func
	   Specifies the depth comparison function. Symbolic constants GL_NEVER, GL_LESS, GL_EQUAL, GL_LEQUAL, GL_GREATER, GL_NOTEQUAL, GL_GEQUAL,
	   and GL_ALWAYS are accepted. The initial value is GL_LESS.

DESCRIPTION

       glDepthFunc specifies the function used to compare each incoming pixel depth value with the depth value present in the depth buffer. The
       comparison is performed only if depth testing is enabled. (See glEnable() and glDisable() of GL_DEPTH_TEST.)

       func specifies the conditions under which the pixel will be drawn. The comparison functions are as follows:

       GL_NEVER
	   Never passes.

       GL_LESS
	   Passes if the incoming depth value is less than the stored depth value.

       GL_EQUAL
	   Passes if the incoming depth value is equal to the stored depth value.

       GL_LEQUAL
	   Passes if the incoming depth value is less than or equal to the stored depth value.

       GL_GREATER
	   Passes if the incoming depth value is greater than the stored depth value.

       GL_NOTEQUAL
	   Passes if the incoming depth value is not equal to the stored depth value.

       GL_GEQUAL
	   Passes if the incoming depth value is greater than or equal to the stored depth value.

       GL_ALWAYS
	   Always passes.

       The initial value of func is GL_LESS. Initially, depth testing is disabled. If depth testing is disabled or if no depth buffer exists, it
       is as if the depth test always passes.

NOTES

       Even if the depth buffer exists and the depth mask is non-zero, the depth buffer is not updated if the depth test is disabled. In order to
       unconditionally write to the depth buffer, the depth test should be enabled and set to GL_ALWAYS.

ERRORS

       GL_INVALID_ENUM is generated if func is not an accepted value.

ASSOCIATED GETS

       glGet() with argument GL_DEPTH_FUNC

       glIsEnabled() with argument GL_DEPTH_TEST

SEE ALSO

       glDepthRange(), glEnable(), glPolygonOffset()

COPYRIGHT

       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014							   GLDEPTHFUNC(3G)

Linux and UNIX Man Pages

glalphafunc(3g) [centos man page]

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