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fglColorTableSGI(3G)	       OpenGL Reference		  fglColorTableSGI(3G)

NAME
     fglColorTableSGI - define a color lookup table

FORTRAN SPECIFICATION
     SUBROUTINE fglColorTableSGI( INTEGER*4 target,
				  INTEGER*4 internalformat,
				  INTEGER*4 width,
				  INTEGER*4 format,
				  INTEGER*4 type,
				  CHARACTER*8 table )

PARAMETERS
     target	     Must be GL_TEXTURE_COLOR_TABLE_SGI, GL_COLOR_TABLE_SGI,
		     GL_POST_CONVOLUTION_COLOR_TABLE_SGI,
		     GL_POST_COLOR_MATRIX_COLOR_TABLE_SGI,
		     GL_PROXY_TEXTURE_COLOR_TABLE_SGI,
		     GL_PROXY_COLOR_TABLE_SGI,
		     GL_PROXY_POST_CONVOLUTION_COLOR_TABLE_SGI, or
		     GL_PROXY_POST_COLOR_MATRIX_COLOR_TABLE_SGI.

     internalformat  The internal format of the color table.  The allowable
		     values are GL_ALPHA, GL_ALPHA4_EXT, GL_ALPHA8_EXT,
		     GL_ALPHA12_EXT, GL_ALPHA16_EXT, GL_LUMINANCE,
		     GL_LUMINANCE4_EXT, GL_LUMINANCE8_EXT, GL_LUMINANCE12_EXT,
		     GL_LUMINANCE16_EXT, GL_LUMINANCE_ALPHA,
		     GL_LUMINANCE4_ALPHA4_EXT, GL_LUMINANCE6_ALPHA2_EXT,
		     GL_LUMINANCE8_ALPHA8_EXT, GL_LUMINANCE12_ALPHA4_EXT,
		     GL_LUMINANCE12_ALPHA12_EXT, GL_LUMINANCE16_ALPHA16_EXT,
		     GL_INTENSITY_EXT, GL_INTENSITY4_EXT, GL_INTENSITY8_EXT,
		     GL_INTENSITY12_EXT, GL_INTENSITY16_EXT, GL_RGB,
		     GL_RGB2_EXT, GL_RGB4_EXT, GL_RGB5_EXT, GL_RGB8_EXT,
		     GL_RGB10_EXT, GL_RGB12_EXT, GL_RGB16_EXT, GL_RGBA,
		     GL_RGBA2_EXT, GL_RGBA4_EXT, GL_RGB5_A1_EXT, GL_RGBA8_EXT,
		     GL_RGB10_A2_EXT, GL_RGBA12_EXT, and GL_RGBA16_EXT.

     width	     The number of entries in the color lookup table specified
		     by table.

     format	     The format of the pixel data in table.  The allowable
		     values are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA,
		     GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB, GL_RGBA, and
		     GL_ABGR_EXT.

     type	     The type of the pixel data in table.  The allowable
		     values are 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, and

									Page 1

fglColorTableSGI(3G)	       OpenGL Reference		  fglColorTableSGI(3G)

		     GL_UNSIGNED_INT_10_10_10_2_EXT.

     table	     Pointer to a one-dimensional array of pixel data that is
		     processed to build the color table.

DESCRIPTION
     fglColorTableSGI is part of the SGI_color_table extension, and is also
     used by the SGI_texture_color_table extension.

     fglColorTableSGI may be used in two ways: to test the actual size and
     color resolution of a lookup table given a particular set of parameters,
     or to load the contents of a color lookup table.  Use the targets
     GL_PROXY_* for the first case and the other targets for the second case.

     If target is GL_TEXTURE_COLOR_TABLE_SGI, GL_COLOR_TABLE_SGI,
     GL_POST_CONVOLUTION_COLOR_TABLE_SGI, or
     GL_POST_COLOR_MATRIX_COLOR_TABLE_SGI, fglColorTableSGI builds a color
     lookup table from an array of pixels.  The pixel array specified by
     width, format, type, and table is extracted from memory and processed
     just as if fglDrawPixels were called, but processing stops after the
     final expansion to RGBA is completed.

     The four scale parameters and the four bias parameters that are defined
     for the table are then used to scale and bias the R, G, B, and A
     components of each pixel.	(Use fglColorTableParameterSGI to set these
     scale and bias parameters.)

     Next, the R, G, B, and A values are clamped to the range [0,1].  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_EXT							R
      GL_RGB		    R	   G	  B
      GL_RGBA		    R	   G	  B	  A

     Finally, the red, green, blue, alpha, luminance, and/or intensity
     components of the resulting pixels are stored in the color table.	They
     form a one-dimensional table with indices in the range [0, width - 1].

     If target is GL_PROXY_*, fglColorTableSGI recomputes and stores the
     values of the proxy color table's state variables
     GL_COLOR_TABLE_FORMAT_SGI, GL_COLOR_TABLE_WIDTH_SGI,
     GL_COLOR_TABLE_RED_SIZE_SGI, GL_COLOR_TABLE_GREEN_SIZE_SGI,
     GL_COLOR_TABLE_BLUE_SIZE_SGI, GL_COLOR_TABLE_ALPHA_SIZE_SGI,

									Page 2

fglColorTableSGI(3G)	       OpenGL Reference		  fglColorTableSGI(3G)

     GL_COLOR_TABLE_LUMINANCE_SIZE_SGI, and GL_COLOR_TABLE_INTENSITY_SIZE_SGI.
     There is no effect on the image or state of any actual color table.  If
     the specified color table is too large to be supported, then all the
     proxy state variables listed above are set to zero.  Otherwise, the color
     table could be supported by fglColorTableSGI using the corresponding
     non-proxy target, and the proxy state variables are set as if that target
     were being defined.

     The proxy state variables can be retrieved by calling
     fglGetColorTableParameterSGI with a target of GL_PROXY_*.	This allows
     the application to decide if a particular fglColorTableSGI command would
     succeed, and determine what the resulting color table attributes would
     be.

     If a color table is enabled, and its width is non-zero, then its contents
     are used to replace a subset of the components of each RGBA pixel group,
     based on the internal format of the table.

     Each pixel group has color components (R, G, B, A) which are in the range
     [0.0, 1.0].  The color components are rescaled to the size of the color
     lookup table to form an index.  Then a subset of the components based on
     the internal format of the table are replaced by the table entry selected
     by that index.  If the color components and contents of the table are
     represented as follows:

		 Representation		      Meaning
		 _________________________________________________
		       r	  Table index computed from R
		       g	  Table index computed from G
		       b	  Table index computed from B
		       a	  Table index computed from A
		      L[i]	  Luminance value at table index i
		      I[i]	  Intensity value at table index i
		      R[i]	  Red value at table index i
		      G[i]	  Green value at table index i
		      B[i]	  Blue value at table index i
		      A[i]	  Alpha value at table index i

     Then the result of color table lookup is as follows:

				       Resulting Texture Components
	       Table Internal Format   R       G       B       A
	       _____________________________________________________
	       GL_ALPHA		       R       G       B       A[a]
	       GL_LUMINANCE	       L[r]    L[g]    L[b]    At
	       GL_LUMINANCE_ALPHA      L[r]    L[g]    L[b]    A[a]
	       GL_INTENSITY	       I[r]    I[g]    I[b]    I[a]
	       GL_RGB		       R[r]    G[g]    B[b]    A
	       GL_RGBA		       R[r]    G[g]    B[b]    A[a]

									Page 3

fglColorTableSGI(3G)	       OpenGL Reference		  fglColorTableSGI(3G)

     When GL_TEXTURE_COLOR_TABLE_SGI is enabled, the filtered colors resulting
     from texturing are mapped by the texture color lookup table. The result
     of the table lookup is passed to the texture environment function to be
     applied to pixel fragments.

     The texture color table can be used to expand the range of colors
     represented by small texels, to select a small ``window'' from a texture
     image with larger dynamic range, to provide simple lighting for volume
     rendering, to implement a restricted kind of color-index texture, or to
     linearize the results of color-space conversions performed by
     multidimensional texturing.

     When GL_COLOR_TABLE_SGI is enabled, the colors resulting from the pixel
     map operation (if it is enabled) are mapped by the color lookup table
     before being passed to the convolution operation. The colors resulting
     from the convolution operation are modified by the post convolution color
     lookup table when GL_POST_CONVOLUTION_COLOR_TABLE_SGI is enabled. These
     modified colors are then sent to the color matrix operation. Finally, if
     GL_POST_COLOR_MATRIX_COLOR_TABLE_SGI is enabled, the colors resulting
     from the color matrix operation are mapped by the post color matrix color
     lookup table before being used by the histogram operation.

NOTES
     If target is set to GL_TEXTURE_COLOR_TABLE_SGI, GL_COLOR_TABLE_SGI,
     GL_POST_CONVOLUTION_COLOR_TABLE_SGI or
     GL_POST_COLOR_MATRIX_COLOR_TABLE_SGI then width must be a power of two or
     a GL_INVALID_VALUE error is generated.  All machines support table widths
     up to and including 256; some machines also support larger tables.

     If target is set to GL_TEXTURE_COLOR_TABLE_SGI and the
     SGI_texture_color_table extension is not supported then an
     GL_INVALID_ENUM error is generated.

     If target is set to GL_COLOR_TABLE_SGI,
     GL_POST_CONVOLUTION_COLOR_TABLE_SGI, or
     GL_POST_COLOR_MATRIX_COLOR_TABLE_SGI and the SGI_color_table extension is
     not supported then an GL_INVALID_ENUM error is generated.

     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.

     See fglIntro for more information on using extensions.

ERRORS
     GL_INVALID_ENUM is generated if target is not one of the allowable
     values.

									Page 4

fglColorTableSGI(3G)	       OpenGL Reference		  fglColorTableSGI(3G)

     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.

     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_TABLE_TOO_LARGE_EXT is generated if the requested color table is too
     large to be supported by the implementation, and target is not a
     GL_PROXY_* target.

     GL_INVALID_OPERATION is generated if fglColorTableSGI is executed between
     the execution of fglBegin and the corresponding execution of fglEnd.

ASSOCIATED GETS
     fglGetColorTableParameterSGI

MACHINE DEPENDENCIES
     On RealityEngine, RealityEngine2, and VTX systems, SGI_color_table is
     supported with these restrictions:

	  1.  Only the texture color table is supported.  The target color
	      table must be GL_TEXTURE_COLOR_TABLE_SGI or
	      GL_PROXY_TEXTURE_COLOR_TABLE_SGI.

	  2. The maximum image width is 256 pixels.

	  3. Only image types GL_UNSIGNED_BYTE and GL_UNSIGNED_SHORT are
	     supported.

	  4. The GL_UNPACK_SWAP_BYTES pixel storage mode is not supported.
	     Calling fglColorTableSGI when GL_UNPACK_SWAP_BYTES is GL_TRUE
	     results in a GL_INVALID_OPERATION error.

	  5. The packed pixel types 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, and GL_UNSIGNED_INT_10_10_10_2_EXT
	     are not supported.

     The SGI_texture_color_table extension is supported on RealityEngine,
     RealityEngine2, and VTX systems and on InfiniteReality systems.

     The SGI_texture_color_table extension is supported on High Impact and
     Maximum Impact.  However, on Indigo2 systems certain combinations of
     texture internal format and texture color table internal format do not
     work:

									Page 5

fglColorTableSGI(3G)	       OpenGL Reference		  fglColorTableSGI(3G)

			  Texture	  Texture Color Table
		     ________________________________________
		     GL_LUMINANCE	  GL_RGB
		     GL_LUMINANCE_ALPHA	  GL_RGB
		     all formats	  GL_RGBA
		     all formats	  GL_INTENSITY

     High Impact and Maximum Impact on Octane systems support all texture
     color table formats except GL_RGBA, or GL_INTENSITY with texture format
     GL_RGBA.

     On High Impact and Maximum Impact systems, the texture color table will
     give incorrect results if GL_FOG_FUNC_SGIS is enabled.

SEE ALSO
     fglColorTableParameterSGI, fglCopyColorTableSGI, fglGetColorTableSGI.

									Page 6

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