fglMinmaxEXT(3G)

NAME
     fglMinmaxEXT - define minmax table


FORTRAN SPECIFICATION
     SUBROUTINE fglMinmaxEXT( INTEGER*4 target,
                              INTEGER*4 internalformat,
                              LOGICAL*1 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
     fglEnable and disabled with fglDisable.

     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 fglGetMinmaxEXT.
     fglMinmaxEXT 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
     fglGetMinmaxParameterEXT 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
     fglMinmaxEXT 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 fglGetString, 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 fglMinmaxEXT is executed between the
     execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGetMinmaxParameterEXT.


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


SEE ALSO
     fglGetMinmaxEXT, fglResetMinmaxEXT.