glColorTableEXT

  • Article

The glColorTableEXT function specifies the format and size of a palette for targeted paletted textures.

void glColorTableEXT(
  GLenum target,  GLenum internalFormat,  GLsizei width,  GLenum format,  GLenum type,  const GLvoid *data);

Parameters

  • target
    The target texture that is to have its palette changed. Must be TEXTURE_1D, TEXTURE_2D, PROXY_TEXTURE_1D, or PROXY_TEXTURE_2D.

  • internalFormat
    The internal format and resolution of the palette. This parameter can assume one of the following symbolic values:

    Constant Base Format R Bits G Bits B Bits A Bits
    GL_R3_G3_B2 GL_RGB 3 3 2
    GL_RGB4 GL_RGB 4 4 4
    GL_RGB5 GL_RGB 5 5 5
    GL_RGB8 GL_RGB 8 8 8
    GL_RGB10 GL_RGB 10 10 10
    GL_RGB12 GL_RGB 12 12 12
    GL_RGB16 GL_RGB 16 16 16
    GL_RGBA2 GL_RGBA 2 2 2 2
    GL_RGBA4 GL_RGBA 4 4 4 4
    GL_RGB5_A1 GL_RGBA 5 5 5 1
    GL_RGBA8 GL_RGBA 8 8 8 8
    GL_RGB10_A2 GL_RGBA 10 10 10 2
    GL_RGB12 GL_RGBA 12 12 12 12
    GL_RGBA16 GL_RGBA 16 16 16 16

  • width
    The size of the palette. Must be 2*n* ≥ 1 for some integer n.

  • format
    The format of the pixel data. The following symbolic constants are accepted:

    Constants Description
    GL_RGBA Each pixel is a group of four components in this order: red, green, blue, alpha. The RGBA format is determined in this way:
    1. The glColorTableEXT function converts floating-point values directly to an internal format with unspecified precision. Signed integer values are mapped linearly to the internal format such that the most positive representable integer value maps to 1.0, and the most negative representable integer value maps to 1.0. Unsigned integer data is mapped similarly: the largest integer value maps to 1.0, and zero maps to 0.0.
    2. The glColorTableEXT function multiplies the resulting color values by GL_c_SCALE and adds them to GL_c_BIAS, where c is RED, GREEN, BLUE, and ALPHA for the respective color components. The results are clamped to the range [0,1].
    3. If GL_MAP_COLOR is TRUE, glColorTableEXT scales each color component by the size of lookup table GL_PIXEL_MAP_c_TO_c, then replaces the component by the value that it references in that table; c is R, G, B, or A, respectively.

    4. The glColorTableEXT function converts the resulting RGBA colors to fragments by attaching the current raster position z-coordinate and texture coordinates to each pixel, then assigning x and y window coordinates to the nth fragment such that

      xn = xr + n mod width

      yn = yr + n/width

      where (xr, yr) is the current raster position.

    5. These pixel fragments are then treated just like the fragments generated by rasterizing points, lines, or polygons. The glColorTableEXT function applies texture mapping, fog, and all the fragment operations before writing the fragments to the framebuffer.
    GL_RED Each pixel is a single red component.

    The glColorTableEXT function converts this component to the internal format in the same way that the red component of an RGBA pixel is, then converts it to an RGBA pixel with green and blue set to 0.0, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel.
    GL_GREEN Each pixel is a single green component.

    The glColorTableEXT function converts this component to the internal format in the same way that the green component of an RGBA pixel is, and then converts it to an RGBA pixel with red and blue set to 0.0, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel.
    GL_BLUE Each pixel is a single blue component.

    The glColorTableEXT function converts this component to the internal format in the same way that the blue component of an RGBA pixel is, and then converts it to an RGBA pixel with red and green set to 0.0, and alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel.
    GL_ALPHA Each pixel is a single alpha component.

    The glColorTableEXT function converts this component to the internal format in the same way that the alpha component of an RGBA pixel is, and then converts it to an RGBA pixel with red, green, and blue set to 0.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel.
    GL_RGB Each pixel is a group of three components in this order: red, green, blue.

    The glColorTableEXT function converts each component to the internal format in the same way that the red, green, and blue components of an RGBA pixel are. The color triple is converted to an RGBA pixel with alpha set to 1.0. After this conversion, the pixel is treated just as if it had been read as an RGBA pixel.
    GL_BGR_EXT Each pixel is a group of three components in this order: blue, green, red.

    GL_BGR_EXT provides a format that matches the memory layout of Windows device-independent bitmaps (DIBs). Thus your applications can use the same data with Win32 function calls and OpenGL pixel function calls.
    GL_BGRA_EXT Each pixel is a group of four components in this order: blue, green, red, alpha.

    GL_BGRA_EXT provides a format that matches the memory layout of Windows device-independent bitmaps (DIBs). Thus your applications can use the same data with Win32 function calls and OpenGL pixel function calls.

  • type
    The data type for data. The following symbolic constants are accepted: GL_UNSIGNED_BYTE, GL_BYTE, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, and GL_FLOAT.

    The following table summarizes the meaning of the valid constants for the type parameter.

    Constant Meaning
    GL_UNSIGNED_BYTE Unsigned 8-bit integer
    GL_BYTE Signed 8-bit integer
    GL_UNSIGNED_SHORT Unsigned 16-bit integer
    GL_SHORT Signed 16-bit integer
    GL_UNSIGNED_INT Unsigned 32-bit integer
    GL_INT 32-bit integer
    GL_FLOAT Single-precision floating-point value

  • data
    A pointer to the paletted texture data. The data is treated as single pixels of a 1-D texture palette entry for a palette entry.

Remarks

Paletted textures are defined with a palette of colors and a set of image data that is composed of indexes to color entries of a palette (a color table).

The glColorTableEXT function specifies the texture palette of a targeted texture. It takes the data from memory and converts the data as if each palette entry is a single pixel of a 1-D texture. The glColorTableEXT function unpacks and converts the data and translates it into an internal format that matches the given format as closely as possible.

If a palette's width is greater than the range of the color indexes in the texture data, some of the palette entries are unused. If a palette's width is less than the range of the color indexes in the texture data, the most significant bits of the texture data are ignored and only the appropriate number of bits in the index are used when accessing the palette. When you specify a proxy target using PROXY_TEXTURE_1D or PROXY_TEXTURE_2D, the palette of the proxy texture is resized and its parameters are set but no data is transferred or accessed.

When the target parameter is GL_PROXY_TEXTURE_1D or GL_PROXY_TEXTURE_2D, and the implementation does not support the values specified for either format or width, glColorTableEXT can fail to create the requested color table. In this case, the color table is empty and all parameters retrieved will be zero. You can determine whether OpenGL supports a particular color table format and size by calling glColorTableEXT with a proxy target, and then calling glGetColorTableParameterivEXT or glGetColorTableParameterfvEXT to determine whether the width parameter matches that set by glColorTableEXT. If the retrieved width is zero, the color table request by glColorTable failed. If the retrieved width is not zero, you can call glColorTable with the real target with TEXTURE_1D or TEXTURE_2D to set the color table.

Note  The glColorTableEXT function is an extension function that is not part of the standard OpenGL library but is part of the GL_EXT_paletted_texture extension. To check whether your implementation of OpenGL supports glColorTableEXT, call glGetString(GL_EXTENSIONS). If it returns GL_EXT_paletted_texture, glColorTableEXT is supported. To obtain the function address of an extension function, call wglGetProcAddress.

To retrieve the actual color table data specified by the glColorTableEXT function, call glGetColorTableEXT. To retrieve the parameters, such as width and format, of the color table specified by the glColorTableEXT function, call the glGetColorTableParameterivEXT or glGetColorTableParameterfvEXT function.

Error Codes

The following are the errors generated and their conditions.

Error code Condition
GL_INVALID_VALUE width was an invalid integer.
GL_INVALID_ENUM target, internalFormat, format, or type was not an accepted value.
GL_INVALID_OPERATION glColorTableEXT was called between glBegin and glEnd pairs.

Requirements

**  Windows NT/2000:** Requires Windows NT 4.0 or later.
**  Windows 95/98:** Requires Windows 95 or later. Available as a redistributable for Windows 95.
**  Header:** Declared in Gl.h.
**  Library:** Use Opengl32.lib.

See Also

glBegin, glColorSubTableEXT, glEnd, glGetColorTableEXT, glGetColorTableParameterfvEXT, glGetColorTableParameterivEXT, wglGetProcAddress