glColorTable

glColorTable 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 a non-zero named buffer object is bound to the GL_PIXEL_UNPACK_BUFFER target (see glBindBuffer ) while a color table is specified, data is treated as a byte offset into the buffer object's data store.

If target is GL_COLOR_TABLE , GL_POST_CONVOLUTION_COLOR_TABLE , or GL_POST_COLOR_MATRIX_COLOR_TABLE , glColorTable builds a color lookup table from an array of pixels. The pixel array specified by width , format , type , and data is extracted from memory and processed just as if glDrawPixels 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 glColorTableParameter to set these scale and bias parameters.)

Next, the R, G, B, and A values are clamped to the range $\left[0,1\right]$ . 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:

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 $\left[0,\mathit{width}-1\right]$ .

If target is GL_PROXY_* , glColorTable recomputes and stores the values of the proxy color table's state variables GL_COLOR_TABLE_FORMAT , GL_COLOR_TABLE_WIDTH , GL_COLOR_TABLE_RED_SIZE , GL_COLOR_TABLE_GREEN_SIZE , GL_COLOR_TABLE_BLUE_SIZE , GL_COLOR_TABLE_ALPHA_SIZE , GL_COLOR_TABLE_LUMINANCE_SIZE , and GL_COLOR_TABLE_INTENSITY_SIZE . 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 glColorTable 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 glGetColorTableParameter with a target of GL_PROXY_* . This allows the application to decide if a particular glColorTable command would succeed, and to 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) that are in the range $\left[0.0,1.0\right]$ . 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:

then the result of color table lookup is as follows:

When GL_COLOR_TABLE 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 is enabled. These modified colors are then sent to the color matrix operation. Finally, if GL_POST_COLOR_MATRIX_COLOR_TABLE 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.

glColorTable is present only if is returned when glGetString is called with an argument of GL_EXTENSIONS .

If target is set to GL_COLOR_TABLE , GL_POST_CONVOLUTION_COLOR_TABLE , or GL_POST_COLOR_MATRIX_COLOR_TABLE , then width must be a power of two or a GL_INVALID_VALUE error is generated.

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

GL_INVALID_ENUM is generated if internalformat 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_VALUE is generated if width is less than zero.

GL_TABLE_TOO_LARGE 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 a non-zero buffer object name is bound to the GL_PIXEL_UNPACK_BUFFER target and the buffer object's data store is currently mapped.

GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_UNPACK_BUFFER target and the data would be unpacked from the buffer object such that the memory reads required would exceed the data store size.

GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_UNPACK_BUFFER target and data is not evenly divisible into the number of bytes needed to store in memory a datum indicated by type .

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

glGetColorTableParameter

glGet with argument GL_PIXEL_UNPACK_BUFFER_BINDING

glColorSubTable , glColorTableParameter , glCopyColorTable , glCopyColorSubTable , glGetColorTable

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/ .