GLCOLORTABLE(3G) UNIX Programmer's Manual GLCOLORTABLE(3G)
glColorTable - define a color lookup table
void glColorTable( GLenum target,
GLenum internalformat,
GLsizei width,
GLenum format,
GLenum type,
const GLvoid *table )
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.
internalformat The internal of the color table. The allow-
able 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.
width The number of entries in the color lookup
table specified by table.
format The of the pixel data in table. The allow-
able values are GL_RED, GL_GREEN, GL_BLUE,
GL_ALPHA, GL_LUMINANCE, GL_LUMINANCE_ALPHA,
GL_RGB, GL_BGR, GL_RGBA, and GL_BGRA.
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,
GL_UNSIGNED_BYTE_2_3_3_REV,
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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.
table Pointer to a one-dimensional array of pixel
data that is processed to build the color
table.
glColorTable may be used in two ways: to test the actual
size and color resolution of a lookup table given a particu-
lar 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_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 table 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 parame-
ters.)
Next, the R, G, B, and A values are clamped to the range
[0, 1]. Each pixel is then converted to the internal speci-
fied by internalformat. This conversion simply maps the com-
ponent values of the pixel (R, G, B, and A) to the values
included in the internal (red, green, blue, alpha, lumi-
nance, and intensity). The mapping is as follows:
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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_*, 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 vari-
ables 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 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 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
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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 opera-
tion are modified by the post convolution color lookup table
when GL_POST_CONVOLUTION_COLOR_TABLE is enabled. These modi-
fied 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 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 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_VALUE is generated if width is less than zero.
GL_INVALID_ENUM is generated if format is not one of the
allowable values.
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GL_INVALID_ENUM is generated if type 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, and tar-
get is not a GL_PROXY_* target.
GL_INVALID_OPERATION is generated if glColorTable is exe-
cuted between the execution of glBegin and the corresponding
execution of glEnd.
glGetColorTableParameter
glColorSubTable(3G), glColorTableParameter(3G),
glCopyColorTable(3G), glCopyColorSubTable(3G),
glGetColorTable(3G)
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