glColorTable(3G) OpenGL Reference 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 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.
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_BGR,
GL_RGBA, GL_BGRA, 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, 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.
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glColorTable(3G) OpenGL Reference glColorTable(3G)
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 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_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 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 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_*, 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
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glColorTable(3G) OpenGL Reference glColorTable(3G)
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
[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]
_____________________________________________________
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
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glColorTable(3G) OpenGL Reference glColorTable(3G)
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 GL_ARB_imaging is returned when
glGetString is called with an argument of GL_EXTENSIONS.
GL_ABGR_EXT is valid only if the EXT_abgr extension is supported.
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.
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 target is not a GL_PROXY_*
target.
GL_INVALID_OPERATION is generated if glColorTable is executed between the
execution of glBegin and the corresponding execution of glEnd.
glGetColorTableParameter
glColorSubTable, glColorTableParameter, glCopyColorTable,
glCopyColorSubTable, glGetColorTable
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