glglobalalphafactorfsun man page on SunOS

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GLGLOBALALPHAFACTORSUN(3gl)			   GLGLOBALALPHAFACTORSUN(3gl)

NAME
       glGlobalAlphaFactorfSUN, glGlobalAlphaFactordSUN, glGlobalAlphaFactorb‐
       SUN,  glGlobalAlphaFactorsSUN,	glGlobalAlphaFactoriSUN,   glGlobalAl‐
       phaFactorubSUN,	glGlobalAlphaFactorusSUN,  glGlobalAlphaFactoruiSUN  -
       set the global alpha factor

C SPECIFICATION
       void glGlobalAlphaFactorfSUN( GLfloat factor )
       void glGlobalAlphaFactordSUN( GLdouble factor )
       void glGlobalAlphaFactorbSUN( GLbyte factor )
       void glGlobalAlphaFactorsSUN( GLshort factor )
       void glGlobalAlphaFactoriSUN( GLint factor )
       void glGlobalAlphaFactorubSUN( GLubyte factor )
       void glGlobalAlphaFactorusSUN( GLushort factor )
       void glGlobalAlphaFactoruiSUN( GLuint factor )

PARAMETERS
       factor  Specifies the global alpha value. The initial value is 1.0.

DESCRIPTION
       Transparency is done in GL using alpha blending. An alpha value of  0.0
       is  used	 for fully transparent objects, while an alpha value of 1.0 is
       used for fully opaque objects.  A value of 0.25 is 75% transparent, and
       so on.

       GL  defines alpha as a component of the vertex color state.  Whenever a
       color is set, the alpha component is set along with the red, green, and
       blue  components.   This means that transparency can not be changed for
       primitives with per-vertex colors without modifying the color  of  each
       vertex, replacing the old alpha component with the new alpha component.
       This can be very expensive for objects  that  are  drawn	 using	vertex
       arrays; it all but precludes the use of display lists.

       This  extension	defines	 a  global alpha attribute that can be used to
       specify an alpha factor that is independent from the alpha component of
       the  color  value.   The global alpha factor is multiplied by the frag‐
       ment's alpha value after primitive rasterization and prior  to  texture
       mapping, replacing the fragment's alpha value.  The global alpha exten‐
       sion is only specified in RGBA mode and must be applied	prior  to  any
       texture	mapping	 operation. Also, global alpha is not applied to pixel
       rectangles and bitmaps.

       If global alpha processing is enabled, then the global alpha factor  is
       multiplied  by  the  incoming  fragment's  alpha	 value.	  This product
       replaces the fragment's alpha value and is passed to subsequent	stages
       in the pipeline.

NOTES
       For  geometric  primitives, a functionally equivalent method to that of
       performing a multiplication for each fragment is to multiply the	 alpha
       values at each vertex of the primitive by the global alpha factor prior
       to the primitive rasterization step.

       glGlobalAlphaFactor*SUN is part of the  GL_SUN_global_alpha  extension,
       not  part  of  the  core	 GL  command  set.   If GL_SUN_global_alpha is
       included in the string returned by glGetString, when called with	 argu‐
       ment  GL_EXTENSIONS,  extension glGlobalAlphaFactor*SUN is supported by
       the connection.

ASSOCIATED GETS
       glGet with arguments GL_GLOBAL_ALPHA_SUN or GL_GLOBAL_ALPHA_FACTOR_SUN

SEE ALSO
       glEnable, glDisable, glIsEnabled, glGetString

				   13 Apr 99	   GLGLOBALALPHAFACTORSUN(3gl)
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