glMinmaxEXT(3G)		       OpenGL Reference		       glMinmaxEXT(3G)



NAME
     glMinmaxEXT - define minmax table


C SPECIFICATION
     void glMinmaxEXT( GLenum target,
		       GLenum internalformat,
		       GLboolean sink )


PARAMETERS
     target	     The minmax	table whose parameters are to be set.  Must be
		     GL_MINMAX_EXT.

     internalformat  The format	of entries in the minmax table.	 Must be one
		     of	GL_ALPHA, GL_ALPHA4_EXT, GL_ALPHA8_EXT,
		     GL_ALPHA12_EXT, GL_ALPHA16_EXT, GL_LUMINANCE,
		     GL_LUMINANCE4_EXT,	GL_LUMINANCE8_EXT, GL_LUMINANCE12_EXT,
		     GL_LUMINANCE16_EXT, GL_LUMINANCE_ALPHA,
		     GL_LUMINANCE4_ALPHA4_EXT, GL_LUMINANCE6_ALPHA2_EXT,
		     GL_LUMINANCE8_ALPHA8_EXT, GL_LUMINANCE12_ALPHA4_EXT,
		     GL_LUMINANCE12_ALPHA12_EXT, GL_LUMINANCE16_ALPHA16_EXT,
		     GL_RGB, GL_RGB2_EXT, GL_RGB4_EXT, GL_RGB5_EXT,
		     GL_RGB8_EXT, GL_RGB10_EXT,	GL_RGB12_EXT, GL_RGB16_EXT,
		     GL_RGBA, GL_RGBA2_EXT, GL_RGBA4_EXT, GL_RGB5_A1_EXT,
		     GL_RGBA8_EXT, GL_RGB10_A2_EXT, GL_RGBA12_EXT, or
		     GL_RGBA16_EXT.

     sink	     If	GL_TRUE, pixels	will be	consumed by the	minmax process
		     and no drawing or texture loading will take place.	 If
		     GL_FALSE, pixels will proceed to the final	conversion
		     process after minmax.

DESCRIPTION
     Minmax is part of the GL pixel transfer process.  It takes	place
     immediately after histogramming.  Minmax is performed only	for RGBA
     pixels (though these may be specified originally as color indices and
     converted to RGBA by index	table lookup).	Minmax is enabled with
     glEnable and disabled with	glDisable.

     When GL_MINMAX_EXT	is enabled, the	RGBA components	of incoming pixels are
     compared to the minimum and maximum values	for each component, which are
     stored in the 2-element minmax table.  (The first element stores the
     minima, and the second element stores the maxima.)	 If a pixel component
     is	greater	than the corresponding component in the	maximum	element, then
     the maximum element is updated with the pixel component value.  If	a
     pixel component is	less than the corresponding component in the minimum
     element, then the minimum element is updated with the pixel component
     value.  (In both cases, if	the internal format of the minmax table
     includes luminance, then the R color component of incoming	pixels is used
     for comparison.)  The contents of the minmax table	may be retrieved at a
     later time	by calling glGetMinmaxEXT.



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glMinmaxEXT(3G)		       OpenGL Reference		       glMinmaxEXT(3G)



     glMinmaxEXT redefines the current minmax table to have entries of the
     format specified by internalformat.  The maximum element is initialized
     with the smallest possible	component values, and the minimum element is
     initialized with the largest possible component values.  The values in
     the previous minmax table,	if any,	are lost.  If sink is GL_TRUE, then
     pixels are	discarded after	minmax;	no further processing of the pixels
     takes place, and no drawing, texture loading, or pixel readback will
     result.

     The minmax	state information may be queried by calling
     glGetMinmaxParameterEXT with a target of GL_MINMAX_EXT and	one of the
     following values for the pname argument:

	       Parameter	    Description
	       ____________________________________________________
	       GL_MINMAX_FORMAT	    Internal format of minmax table
	       GL_MINMAX_SINK_EXT   Value of the sink parameter


NOTES
     glMinmaxEXT is part of the	EXT_blend_minmax extension, not	part of	the
     core GL command set. If GL_EXT_blend_minmax is included in	the string
     returned by glGetString, when called with argument	GL_EXTENSIONS,
     extension EXT_blend_minmax	is supported by	the connection.


ERRORS
     GL_INVALID_ENUM is	generated if target is not one of the allowable
     values.

     GL_INVALID_ENUM is	generated if internalformat is not one of the
     allowable values.

     GL_INVALID_OPERATION is generated if glMinmaxEXT is executed between the
     execution of glBegin and the corresponding	execution of glEnd.

ASSOCIATED GETS
     glGetMinmaxParameterEXT.


MACHINE	DEPENDENCIES
     On	RealityEngine, RealityEngine2, and VTX systems,	histogram and minmax
     may not be	used when rendering to pixmaps.


SEE ALSO
     glGetMinmaxEXT, glResetMinmaxEXT.








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