glCopyConvolutionFilter2D(3G)

NAME
     glCopyConvolutionFilter2D - copy pixels into a two-dimensional
     convolution 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 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.

     x, y            The window space coordinates of the lower-left coordinate
                     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
     associated 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 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_ALPHA                                    A
      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.

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

     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
     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
     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_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
     executed between the execution of glBegin and the corresponding execution
     of glEnd.

ASSOCIATED GETS
     glGetConvolutionParameter, glGetConvolutionFilter


SEE ALSO
     glConvolutionFilter2D, glConvolutionParameter, glPixelTransfer