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glalphafunc(3g) [xfree86 man page]

GLALPHAFUNC(3G) 														   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 repre- sents 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 refer- ence 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 speci- fied 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 bit- maps, 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(3G), glClear(3G), glDepthFunc(3G), glEnable(3G), glStencilFunc(3G) GLALPHAFUNC(3G)

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GLDEPTHFUNC(3G) 														   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. 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. ERRORS
GL_INVALID_ENUM is generated if func is not an accepted value. GL_INVALID_OPERATION is generated if glDepthFunc is executed between the execution of glBegin and the corresponding execution of glEnd. ASSOCIATED GETS
glGet with argument GL_DEPTH_FUNC glIsEnabled with argument GL_DEPTH_TEST SEE ALSO
glDepthRange(3G), glEnable(3G), glPolygonOffset(3G) GLDEPTHFUNC(3G)
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