|
Table of Contents
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 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 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, 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,
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 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
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
(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 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 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 |
| 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.
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.
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(3G)
, glColorTableParameter(3G)
,
glCopyColorTable(3G)
, glCopyColorSubTable(3G)
, glGetColorTable(3G)
Table of Contents
|
