glGetConvolutionFilterEXT(3G)

NAME
     glGetConvolutionFilterEXT - get current 1D or 2D convolution filter
     kernel


C SPECIFICATION
     void glGetConvolutionFilterEXT( GLenum target,
                                     GLenum format,
                                     GLenum type,
                                     GLvoid *image )


PARAMETERS
     target  The filter to be retrieved.  Must be one of GL_CONVOLUTION_1D_EXT
             or GL_CONVOLUTION_2D_EXT.

     format  Format of the output image.  Must be one of GL_RED, GL_GREEN,
             GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_ABGR_EXT, GL_LUMINANCE, or
             GL_LUMINANCE_ALPHA.

     type    Data type of components in the output image.  Must be one of
             GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT,
             GL_UNSIGNED_INT, GL_INT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2_EXT,
             GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
             GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT.

     image   Pointer to storage for the output image.

DESCRIPTION
     glGetConvolutionFilterEXT returns the current 1D or 2D convolution filter
     kernel as an image.  The one- or two-dimensional image is placed in image
     according to the specifications in format and type.  No pixel transfer
     operations are performed on this image, but the relevant pixel storage
     modes are applied.

     Color components that are present in format but not included in the
     internal format of the filter are returned as zero.  The assignments of
     internal color components to the components of format are as follows:

                     Internal Component   Resulting Component
                     ________________________________________
                     red                  red
                     green                green
                     blue                 blue
                     alpha                alpha
                     luminance            red
                     intensity            red

NOTES
     The current separable 2D filter must be retrieved with
     glGetSeparableFilterEXT rather than glGetConvolutionFilterEXT.
ERRORS
     GL_INVALID_ENUM is generated if target is not one of the allowable
     values.

     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 glGetConvolutionFilterEXT is
     executed between the execution of glBegin and the corresponding execution
     of glEnd.

     If type is set to GL_UNSIGNED_BYTE_3_3_2_EXT,
     GL_UNSIGNED_SHORT_4_4_4_4_EXT, GL_UNSIGNED_SHORT_5_5_5_1_EXT,
     GL_UNSIGNED_INT_8_8_8_8_EXT, or GL_UNSIGNED_INT_10_10_10_2_EXT and the
     EXT_packed_pixels extension is not supported then a GL_INVALID_ENUM error
     is generated.

ASSOCIATED GETS
     glGetConvolutionParameterEXT


MACHINE DEPENDENCIES
     On RealityEngine, RealityEngine2, and VTX systems convolution may not be
     used in the following circumstances:

          1.  When rendering to pixmaps.

          2.  When fragment processing (texturing, depth buffering, alpha
              testing, multisampling, fog) is enabled.

          3.  When histogramming or minmax is enabled.

          4.  When either of the pixel zoom factors has a value other than 1.0
              or -1.0.

     In these cases, glDrawPixels and glCopyPixels report a
     GL_INVALID_OPERATION error and do not transfer any pixels.


SEE ALSO
     glGetSeparableFilterEXT, glConvolutionParameterEXT,
     glConvolutionFilter1DEXT, glConvolutionFilter2DEXT.