glGetConvolutionFilterEXT(3G)  OpenGL Reference	 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.




									Page 1






glGetConvolutionFilterEXT(3G)  OpenGL Reference	 glGetConvolutionFilterEXT(3G)



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.

     Loading a convolution filter with some combinations of pixel transfer
     modes may be unreliable on	InfiniteReality	systems.  Straightforward
     transfers are known to work, though.  The remaining problems will be
     fixed in the next release.

     On	InfiniteReality	systems, kernel	values are clamped to the range
     [0.0,1.0] when they are retrieved.	 This will be fixed in a future
     release.







									Page 2






glGetConvolutionFilterEXT(3G)  OpenGL Reference	 glGetConvolutionFilterEXT(3G)



SEE ALSO
     glGetSeparableFilterEXT, glConvolutionParameterEXT,
     glConvolutionFilter1DEXT, glConvolutionFilter2DEXT.




















































									Page 3