glSeparableFilter2D(3G)

NAME
     glSeparableFilter2D - define a separable two-dimensional convolution
     filter


C SPECIFICATION
     void glSeparableFilter2D( GLenum target,
                               GLenum internalformat,
                               GLsizei width,
                               GLsizei height,
                               GLenum format,
                               GLenum type,
                               const GLvoid *row,
                               const GLvoid *column )


PARAMETERS
     target          Must be GL_SEPARABLE_2D.

     internalformat  The internal format of the convolution filter kernel.
                     The allowable values are GL_ALPHA, GL_ALPHA4, GL_ALPHA8,
                     GL_ALPHA12, GL_ALPHA16, GL_LUMINANCE, GL_LUMINANCE4,
                     GL_LUMINANCE8, GL_LUMINANCE12, GL_LUMINANCE16,
                     GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4,
                     GL_LUMINANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8,
                     GL_LUMINANCE12_ALPHA4, GL_LUMINANCE12_ALPHA12,
                     GL_LUMINANCE16_ALPHA16, GL_INTENSITY, GL_INTENSITY4,
                     GL_INTENSITY8, GL_INTENSITY12, GL_INTENSITY16,
                     GL_R3_G3_B2, GL_RGB, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10,
                     GL_RGB12, GL_RGB16, GL_RGBA, GL_RGBA2, GL_RGBA4,
                     GL_RGB5_A1, GL_RGBA8, GL_RGB10_A2, GL_RGBA12, or
                     GL_RGBA16.

     width           The number of elements in the pixel array referenced by
                     row.  (This is the width of the separable filter kernel.)

     height          The number of elements in the pixel array referenced by
                     column.  (This is the height of the separable filter
                     kernel.)

     format          The format of the pixel data in row and column.  The
                     allowable values are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA,
                     GL_RGB, GL_BGR, GL_RGBA, GL_BGRA, GL_ABGR_EXT,
                     GL_INTENSITY, GL_LUMINANCE, and GL_LUMINANCE_ALPHA.

     type            The type of the pixel data in row and column.  Symbolic
                     constants GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP,
                     GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT,
                     GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2,
                     GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5,
                     GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4,
                     GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1,
                     GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8,
                     GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2,
                     and GL_UNSIGNED_INT_2_10_10_10_REV are accepted.

     row             Pointer to a one-dimensional array of pixel data that is
                     processed to build the row filter kernel.

     column          Pointer to a one-dimensional array of pixel data that is
                     processed to build the column filter kernel.

DESCRIPTION
     glSeparableFilter2D builds a two-dimensional separable convolution filter
     kernel from two arrays of pixels.

     The pixel arrays specified by (width, format, type, row) and (height,
     format, type, column) are processed just as if they had been passed to
     glDrawPixels, but processing stops after the final expansion to RGBA is
     completed.

     Next, the R, G, B, and A components of all pixels in both arrays are
     scaled by the four separable 2D GL_CONVOLUTION_FILTER_SCALE parameters
     and biased by the four separable 2D GL_CONVOLUTION_FILTER_BIAS
     parameters.  (The scale and bias parameters are set by
     glConvolutionParameter using the GL_SEPARABLE_2D target and the names
     GL_CONVOLUTION_FILTER_SCALE and GL_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.

     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:

     ________________________________________________________________________
      Internal Format      Red   Green   Blue   Alpha   Luminance   Intensity
      _______________________________________________________________________
      GL_LUMINANCE                                          R
      GL_LUMINANCE_ALPHA                          A         R
      GL_INTENSITY                                                      R
      GL_RGB                R      G      B
      GL_RGBA               R      G      B       A
      _______________________________________________________________________


     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 two one-dimensional filter kernel images.  The row
     image is indexed by coordinate i starting at zero and increasing from
     left to right.  Each location in the row image is derived from element i
     of row.  The column image is indexed by coordinate j starting at zero and
     increasing from bottom to top.  Each location in the column image is
     derived from element j of column.

     Note that after a convolution is performed, the resulting color
     components are also scaled by their corresponding
     GL_POST_CONVOLUTION_c_SCALE parameters and biased by their corresponding
     GL_POST_CONVOLUTION_c_BIAS parameters (where c takes on the values RED,
     GREEN, BLUE, and ALPHA).  These parameters are set by glPixelTransfer.

NOTES
     glSeparableFilter2D is present only if GL_ARB_imaging is returned when
     glGetString is called with an argument of GL_EXTENSIONS.

     GL_ABGR_EXT is valid only if the EXT_abgr extension is supported.

ERRORS
     GL_INVALID_ENUM is generated if target is not GL_SEPARABLE_2D.

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

     GL_INVALID_VALUE is generated if width is less than zero or greater than
     the maximum supported value.  This value may be queried with
     glGetConvolutionParameter using target GL_SEPARABLE_2D and name
     GL_MAX_CONVOLUTION_WIDTH.

     GL_INVALID_VALUE is generated if height is less than zero or greater than
     the maximum supported value.  This value may be queried with
     glGetConvolutionParameter using target GL_SEPARABLE_2D and name
     GL_MAX_CONVOLUTION_HEIGHT.

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

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

     GL_INVALID_OPERATION is generated if glSeparableFilter2D is executed
     between the execution of glBegin and the corresponding execution of
     glEnd.

     GL_INVALID_OPERATION is generated if height is one of
     GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV,
     GL_UNSIGNED_SHORT_5_6_5, or GL_UNSIGNED_SHORT_5_6_5_REV and format is not
     GL_RGB.

     GL_INVALID_OPERATION is generated if height is one of
     GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV,
     GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV,
     GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV,
     GL_UNSIGNED_INT_10_10_10_2, or GL_UNSIGNED_INT_2_10_10_10_REV and format
     is not GL_RGBA, GL_BGRA or GL_ABGR_EXT.

ASSOCIATED GETS
     glGetConvolutionParameter, glGetSeparableFilter


SEE ALSO
     glConvolutionFilter1D, glConvolutionFilter2D, glConvolutionParameter,
     glPixelTransfer