1991-2006 Silicon Graphics, Inc.
glCopyColorTable 3G
glCopyColorTable copy pixels into a color table

## C Specification

void `glCopyColorTable` GLenum target GLenum internalformat GLint x GLint y GLsizei width

## Parameters

target

  The color table target. Must be `GL_COLOR_TABLE`, `GL_POST_CONVOLUTION_COLOR_TABLE`, or `GL_POST_COLOR_MATRIX_COLOR_TABLE`.

internalformat

  The internal storage format of the texture image. Must be one of the following symbolic constants: `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

  The x coordinate of the lower-left corner of the pixel rectangle to be transferred to the color table.

y

  The y coordinate of the lower-left corner of the pixel rectangle to be transferred to the color table.

width

  The width of the pixel rectangle.

## Description

`glCopyColorTable` loads a color table with pixels from the current `GL_READ_BUFFER` (rather than from main memory, as is the case for glColorTable).

The screen-aligned pixel rectangle with lower-left corner at (x,\ y) having width width and height 1 is loaded into the color table. 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 just as if glReadPixels were called, with internalformat set to RGBA, but processing stops after the final conversion to RGBA.

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. The scale and bias parameters are set by calling glColorTableParameter.

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` |  |  |  |  |  | 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 .

## Notes

`glCopyColorTable` is available only if `ARB_imaging` is returned from calling glGetString with an argument of `GL_EXTENSIONS`.

## Errors

`GL_INVALID_ENUM` is generated when target is not one of the allowable values.

`GL_INVALID_VALUE` is generated if width is less than zero.

`GL_INVALID_VALUE` is generated if internalformat is not one of the allowable values.

`GL_TABLE_TOO_LARGE` is generated if the requested color table is too large to be supported by the implementation.

`GL_INVALID_OPERATION` is generated if `glCopyColorTable` is executed between the execution of glBegin and the corresponding execution of glEnd.

## Associated Gets

glGetColorTable, glGetColorTableParameter

## See Also

glColorTable, glColorTableParameter, glReadPixels

## Copyright

Copyright 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.