fglGetConvolutionFilterEXT(3G)

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


FORTRAN SPECIFICATION
     SUBROUTINE fglGetConvolutionFilterEXT( INTEGER*4 target,
                                            INTEGER*4 format,
                                            INTEGER*4 type,
                                            CHARACTER*8 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
     fglGetConvolutionFilterEXT 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
     fglGetSeparableFilterEXT rather than fglGetConvolutionFilterEXT.
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 fglGetConvolutionFilterEXT is
     executed between the execution of fglBegin and the corresponding
     execution of fglEnd.

     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
     fglGetConvolutionParameterEXT


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, fglDrawPixels and fglCopyPixels report a
     GL_INVALID_OPERATION error and do not transfer any pixels.


SEE ALSO
     fglGetSeparableFilterEXT, fglConvolutionParameterEXT,
     fglConvolutionFilter1DEXT, fglConvolutionFilter2DEXT.