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_C_ 
_C_ Original Code. The Original Code is: OpenGL Sample Implementation,
_C_ Version 1.2.1, released January 26, 2000, developed by Silicon Graphics,
_C_ Inc. The Original Code is Copyright (c) 1991-2000 Silicon Graphics, Inc.
_C_ Copyright in any portions created by third parties is as indicated
_C_ elsewhere herein. All Rights Reserved.
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_C_ Additional Notice Provisions: The application programming interfaces
_C_ established by SGI in conjunction with the Original Code are The
_C_ OpenGL(R) Graphics System: A Specification (Version 1.2.1), released
_C_ April 1, 1999; The OpenGL(R) Graphics System Utility Library (Version
_C_ 1.3), released November 4, 1998; and OpenGL(R) Graphics with the X
_C_ Window System(R) (Version 1.3), released October 19, 1998. This software
_C_ was created using the OpenGL(R) version 1.2.1 Sample Implementation
_C_ published by SGI, but has not been independently verified as being
_C_ compliant with the OpenGL(R) version 1.2.1 Specification.
_C_
_C_ The first character in this file must be an '_'!
_C_ Anything on a line after _C_ is ignored
_define(_filters,tbl)_C_
_header(ConvolutionFilter2D,define a two-dimensional convolution filter)
_names(ConvolutionFilter2D)
_define(@<__target>@,@<_param1>@)_C_
_define(@<__internalformat>@,@<_param2>@)_C_
_define(@<__width>@,@<_param3>@)_C_
_define(@<__height>@,@<_param4>@)_C_
_define(@<__format>@,@<_param5>@)_C_
_define(@<__type>@,@<_param6>@)_C_
_define(@<__image>@,@<_param7>@)_C_
.SH PARAMETERS
_phead(__target)
Must be _const(CONVOLUTION_2D).
_phead(__internalformat)
The internal format of the convolution filter kernel.
The allowable values are
_const(ALPHA),
_const(ALPHA4),
_const(ALPHA8),
_const(ALPHA12),
_const(ALPHA16),
_const(LUMINANCE),
_const(LUMINANCE4),
_const(LUMINANCE8),
_const(LUMINANCE12),
_const(LUMINANCE16),
_const(LUMINANCE_ALPHA),
_const(LUMINANCE4_ALPHA4),
_const(LUMINANCE6_ALPHA2),
_const(LUMINANCE8_ALPHA8),
_const(LUMINANCE12_ALPHA4),
_const(LUMINANCE12_ALPHA12),
_const(LUMINANCE16_ALPHA16),
_const(INTENSITY),
_const(INTENSITY4),
_const(INTENSITY8),
_const(INTENSITY12),
_const(INTENSITY16),
_const(R3_G3_B2),
_const(RGB),
_const(RGB4),
_const(RGB5),
_const(RGB8),
_const(RGB10),
_const(RGB12),
_const(RGB16),
_const(RGBA),
_const(RGBA2),
_const(RGBA4),
_const(RGB5_A1),
_const(RGBA8),
_const(RGB10_A2),
_const(RGBA12), or
_const(RGBA16).
_phead(__width)
The width of the pixel array referenced by __image.
_phead(__height)
The height of the pixel array referenced by __image.
_phead(__format)
The format of the pixel data in __image.
The allowable values are
_const(RED),
_const(GREEN),
_const(BLUE),
_const(ALPHA),
_const(RGB),
_const(BGR),
_const(RGBA),
_const(BGRA),
_const(LUMINANCE), and
_const(LUMINANCE_ALPHA).
_phead(__type)
The type of the pixel data in __image.
Symbolic constants
_const(UNSIGNED_BYTE),
_const(BYTE),
_const(BITMAP),
_const(UNSIGNED_SHORT),
_const(SHORT),
_const(UNSIGNED_INT),
_const(INT),
_const(FLOAT),
_const(UNSIGNED_BYTE_3_3_2),
_const(UNSIGNED_BYTE_2_3_3_REV),
_const(UNSIGNED_SHORT_5_6_5),
_const(UNSIGNED_SHORT_5_6_5_REV),
_const(UNSIGNED_SHORT_4_4_4_4),
_const(UNSIGNED_SHORT_4_4_4_4_REV),
_const(UNSIGNED_SHORT_5_5_5_1),
_const(UNSIGNED_SHORT_1_5_5_5_REV),
_const(UNSIGNED_INT_8_8_8_8),
_const(UNSIGNED_INT_8_8_8_8_REV),
_const(UNSIGNED_INT_10_10_10_2), and
_const(UNSIGNED_INT_2_10_10_10_REV)
are accepted.
_phead(__image)
Pointer to a two-dimensional array of pixel data that is processed to
build the convolution filter kernel.
.SH DESCRIPTION
_cmnd builds a two-dimensional convolution filter kernel from an array of
pixels.
.sp
The pixel array specified by __width, __height, __format, __type, and
__image is extracted from memory and processed just as if
_cmnd(DrawPixels) were called, but processing stops after the final
expansion to RGBA is completed.
.sp
The R, G, B, and A components of each pixel are next scaled by the four
2D _const(CONVOLUTION_FILTER_SCALE) parameters and biased by the
four 2D _const(CONVOLUTION_FILTER_BIAS) parameters.
(The scale and bias parameters are set by _cmnd(ConvolutionParameter)
using the _const(CONVOLUTION_2D) target and the names
_const(CONVOLUTION_FILTER_SCALE) and _const(CONVOLUTION_FILTER_BIAS).
The parameters themselves are vectors of four values that are applied to red,
green, blue, and alpha, in that order.)
The R, G, B, and A values are not clamped to [0,1] at any time during this
process.
.sp
Each pixel is then converted to the internal format specified by
__internalformat.
This conversion simply maps the component values of the pixel (R, G, B,
and A) to the values included in the internal format (red, green, blue,
alpha, luminance, and intensity).  The mapping is as follows:
.sp
.TS
center;
lb cb cb cb cb cb cb
l c c c c c c.
_
Internal Format	Red	Green	Blue	Alpha	Luminance	Intensity
_
_const(ALPHA)				A
_const(LUMINANCE)				R
_const(LUMINANCE_ALPHA)			A	R
_const(INTENSITY)						R
_const(RGB)	R	G	B
_const(RGBA)	R	G	B	A
_
.TE
.sp
The red, green, blue, alpha, luminance, and/or intensity components of
the resulting pixels are stored in floating-point rather than integer
format.
They form a two-dimensional filter kernel image indexed with coordinates
\f2i\fP and \f2j\fP such that \f2i\fP starts at zero and increases from left
to right, and \f2j\fP starts at zero and increases from bottom to top.
Kernel location \f2i,j\fP is derived from the \f2N\fPth pixel,
where \f2N\fP is \f2i\fP+\f2j\fP*__width.
.PP
Note that after a convolution is performed, the resulting color
components are also scaled by their corresponding
_const(POST_CONVOLUTION_c_SCALE) parameters and biased by their
corresponding _const(POST_CONVOLUTION_c_BIAS) parameters (where
\f2c\fP takes on the values \f3RED\fP, \f3GREEN\fP, \f3BLUE\fP, and
\f3ALPHA\fP).
These parameters are set by _cmnd(PixelTransfer).
.SH NOTES
_cmnd is present only if _arbstring(imaging) is returned when _cmnd(GetString)
is called with an argument of _const(EXTENSIONS).
.SH ERRORS
_const(INVALID_ENUM) is generated if __target is not
_const(CONVOLUTION_2D).
.P
_const(INVALID_ENUM) is generated if __internalformat is not one of the
allowable values.
.P
_const(INVALID_VALUE) is generated if __width is less than zero or greater
than the maximum supported value.
This value may be queried with _cmnd(GetConvolutionParameter)
using target _const(CONVOLUTION_2D) and name
_const(MAX_CONVOLUTION_WIDTH).
.P
_const(INVALID_VALUE) is generated if __height is less than zero or greater
than the maximum supported value.
This value may be queried with _cmnd(GetConvolutionParameter)
using target _const(CONVOLUTION_2D) and name
_const(MAX_CONVOLUTION_HEIGHT).
.P
_const(INVALID_ENUM) is generated if __format is not one of the allowable
values.
.P
_const(INVALID_ENUM) is generated if __type is not one of the allowable
values.
.P
_const(INVALID_OPERATION) is generated if _cmnd is executed
between the execution of _cmnd(Begin) and the corresponding
execution of _cmnd(End).
.P
_const(INVALID_OPERATION) is generated if _param4 is one of
_const(UNSIGNED_BYTE_3_3_2),
_const(UNSIGNED_BYTE_2_3_3_REV),
_const(UNSIGNED_SHORT_5_6_5), or
_const(UNSIGNED_SHORT_5_6_5_REV)
and _param5 is not _const(RGB).
.P
_const(INVALID_OPERATION) is generated if _param4 is one of
_const(UNSIGNED_SHORT_4_4_4_4),
_const(UNSIGNED_SHORT_4_4_4_4_REV),
_const(UNSIGNED_SHORT_5_5_5_1),
_const(UNSIGNED_SHORT_1_5_5_5_REV),
_const(UNSIGNED_INT_8_8_8_8),
_const(UNSIGNED_INT_8_8_8_8_REV),
_const(UNSIGNED_INT_10_10_10_2), or
_const(UNSIGNED_INT_2_10_10_10_REV)
and _param5 is neither _const(RGBA) nor _const(BGRA).
.SH ASSOCIATED GETS
_cmnd(GetConvolutionParameter), _cmnd(GetConvolutionFilter)
.SH SEE ALSO
_cmnd(ConvolutionFilter1D),
_cmnd(SeparableFilter2D),
_cmnd(ConvolutionParameter),
_cmnd(PixelTransfer)