glGetColorTableEXT function

Artikkel
08/19/2021

The glGetColorTableEXT function gets the color table data of the current targeted texture palette.

Syntax

void WINAPI glGetColorTableEXT(
         GLenum target,
         GLenum format,
         GLenum type,
   const GLvoid *data
);

Parameters

target

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

format

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

Value	Meaning
GL_RGBA	Each pixel is a group of four components in the following order: red, green, blue, alpha. The RGBA format is determined in this way: The glGetColorTableEXT 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. The glGetColorTableEXT 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]. If GL_MAP_COLOR is TRUE, glGetColorTableEXT 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. The glGetColorTableEXT 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 x? = x_r + n mod width y? = y_r + n/width where (x_r , y_r ) is the current raster position. These pixel fragments are then treated just like the fragments generated by rasterizing points, lines, or polygons. The glGetColorTableEXT 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 glGetColorTableEXT 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 glGetColorTableEXT 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 glGetColorTableEXT 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 glGetColorTableEXT 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 glGetColorTableEXT 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 Microsoft Windows device-independent bitmaps (DIBs). Thus, your applications can use the same data with Windows 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 Windows function calls and OpenGL pixel function calls.

type

The data type for data. The following are the accepted symbolic constants and their meanings.

Value	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

Points to the location where returned color table information is to be stored. Each color table entry is stored as if it was a single pixel of a 1-D texture. Because all textures have a default palette, glGetColorTableEXT always returns palette information even if the texture data is not in a paletted format.

Return value

This function does not return a value.

Error codes

The following error codes can be retrieved by the glGetError function.

Name	Meaning
GL_INVALID_ENUM	target, format, or type was not an accepted value.
GL_INVALID_OPERATION	The function was called between a call to glBegin and the corresponding call to glEnd.

Remarks

The glGetColorTableEXT function gets the actual color table data specified by glColorTableEXT and glColorSubTableEXT.

The glGetColorTableEXT 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 glGetColorTableEXT, call glGetString(GL_EXTENSIONS). If it returns GL_EXT_paletted_texture, glGetColorTableEXT is supported. To obtain the function address of an extension function, call wglGetProcAddress.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Gl.h

Del via