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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