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GLCOPYCONVOLUTIONFILTER2D(3G)			 GLCOPYCONVOLUTIONFILTER2D(3G)

NAME
       glCopyConvolutionFilter2D - copy pixels into a two-dimensional convolu‐
       tion filter

C SPECIFICATION
       void glCopyConvolutionFilter2D( GLenum target,
				       GLenum internalformat,
				       GLint x,
				       GLint y,
				       GLsizei width,
				       GLsizei height )

PARAMETERS
       target	       Must be GL_CONVOLUTION_2D.

       internalformat  The internal  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.

       x, y	       The window space coordinates of the lower-left  coordi‐
		       nate of the pixel array to copy.

       width	       The width of the pixel array to copy.

       height	       The height of the pixel array to copy.

DESCRIPTION
       glCopyConvolutionFilter2D  defines a two-dimensional convolution filter
       kernel with pixels from the current GL_READ_BUFFER  (rather  than  from
       main memory, as is the case for glConvolutionFilter2D).

       The  screen-aligned  pixel  rectangle with lower-left corner at (x, y),
       width width and height height is used to define the convolution filter.
       If any pixels within this region are outside the window that is associ‐
       ated with the GL context, the values  obtained  for  those  pixels  are
       undefined.

       The  pixels  in	the rectangle are processed exactly as if glReadPixels
       had been called with format set to RGBA, but  the  process  stops  just
       before  final  conversion.  The R, G, B, and A components of each pixel
       are next scaled by the four 2D  GL_CONVOLUTION_FILTER_SCALE  parameters
       and  biased by the four 2D GL_CONVOLUTION_FILTER_BIAS parameters.  (The
       scale and bias parameters are set by glConvolutionParameter  using  the
       GL_CONVOLUTION_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  specified by internalfor‐
       mat.  This conversion simply maps the component values of the pixel (R,
       G, B, and A) to the values included in the internal  (red, green, blue,
       alpha, luminance, and intensity).  The mapping is as follows:

	Internal Format	    Channel mapping
	GL_ALPHA	    A=Alpha
	GL_LUMINANCE	    R=Luminance
	GL_LUMINANCE_ALPHA  A=Alpha, R=Luminance
	GL_INTENSITY	    R=Intensity
	GL_RGB		    R=Red, G=Green, B=Blue
	GL_RGBA		    R=Red, G=Green, B=Blue, A=Alpha

       The red, green, blue, alpha, luminance, and/or intensity components  of
       the resulting pixels are stored in floating-point rather than integer

       Pixel  ordering	is  such that lower x screen coordinates correspond to
       lower i filter image coordinates, and lower y screen coordinates corre‐
       spond to lower j filter image coordinates.

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

NOTES
       glCopyConvolutionFilter2D is present only if GL_ARB_imaging is returned
       when glGetString is called with an argument of GL_EXTENSIONS.

ERRORS
       GL_INVALID_ENUM is generated if target is not GL_CONVOLUTION_2D.

       GL_INVALID_ENUM is generated if internalformat is not one of the allow‐
       able 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_CONVOLUTION_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_CONVOLUTION_2D  and  name
       GL_MAX_CONVOLUTION_HEIGHT.

       GL_INVALID_OPERATION is generated if glCopyConvolutionFilter2D is  exe‐
       cuted  between the execution of glBegin and the corresponding execution
       of glEnd.

ASSOCIATED GETS
       glGetConvolutionParameter, glGetConvolutionFilter

SEE ALSO
       glConvolutionFilter2D, glConvolutionParameter, glPixelTransfer

						 GLCOPYCONVOLUTIONFILTER2D(3G)
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