C SPECIFICATION
void GLAPIENTRY glColorTable( GLenum target,
GLenum internalforma )
PARAMETERS
target Must be one of GL_COLOR_TABLE,
GL_POST_CONVOLUTION_COLOR_TABLE,
GL_POST_COLOR_MATRIX_COLOR_TABLE, GL_PROXY_COLOR_TABLE,
GL_PROXY_POST_CONVOLUTION_COLOR_TABLE, or
GL_PROXY_POST_COLOR_MATRIX_COLOR_TABLE.
internalforma The internal format of the color table. 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, and GL_RGBA16.
_param3 The number of entries in the color lookup table speci-
fied by _param6.
_param4 The format of the pixel data in _param6. The allowable
values are GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA,
GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB, GL_BGR,
GL_RGBA, and GL_BGRA.
_param5 The type of the pixel data in _param6. 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, GL_UNSIGNED_BYTE_2_3_3_REV,
GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV,
GL_UNSIGNED_SHORT_4_4_4_4,
GL_UNSIGNED_SHORT_4_4_4_4_REV,
GL_UNSIGNED_SHORT_5_5_5_1,
GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8,
GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2,
and GL_UNSIGNED_INT_2_10_10_10_REV.
_param6 Pointer to a one-dimensional array of pixel data that is
processed to build the color table.
DESCRIPTION
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
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 internal-
forma. 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 fol-
lows:
------------------------------------------------------------------------
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 com-
ponents of the resulting pixels are stored in the color table. They
form a one-dimensional table with indices in the range
[0, _param3 - 1].
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 suc-
ceed, 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 con-
tents 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 [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
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]
-----------------------------------------------------
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.
NOTES
glColorTable is present only if GL_ARB_imaging 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 _param3 must be a power of two
or a GL_INVALID_VALUE error is generated.
ERRORS
GL_INVALID_ENUM is generated if target is not one of the allowable val-
ues.
GL_INVALID_ENUM is generated if internalforma is not one of the allow-
able values.
GL_INVALID_VALUE is generated if _param3 is less than zero.
glGetColorTableParameter
SEE ALSO
glColorSubTable, glColorTableParameter, glCopyColorTable,
glCopyColorSubTable, glGetColorTable
GLCOLORTABLE(3G)
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