glCopyPixels

NAME

C SPECIFICATION

void glCopyPixels(GLint x,
                  GLint y,
                  GLsizei width,
                  GLsizei height,
                  GLenum type)

PARAMETERS

DESCRIPTION

x and y specify the window coordinates of the lower left corner of the rectangular region to be copied. width and height specify the dimensions of the rectangular region to be copied. Both width and height must not be negative.

Several parameters control the processing of the pixel data while it is being copied. These parameters are set with three commands: glPixelTransfer, glPixelMap, and glPixelZoom. This reference page describes the effects on glCopyPixel of most, but not all, of the parameters specified by these three commands.

glCopyPixel copies values from each pixel with lower left corner at (x + i, y + j) for 0 < i < width and 0 < j < height. This pixel is said to be the i^th pixel in the j^th row. Pixels are returned in row order from the lowest to the highest row, left to right in each row.

If GL_INTERLACE_READ_I3D is enabled, every other row is read. The j^th row is read from the window coordinate (x, y + j * 2).

type specifies whether color, depth, or stencil data is to be copied. The details of the transfer for each data type are as follows:

GL_COLOR

Indices or RGBA colors are read from the buffer currently specified as the read source buffer (see glReadBuffer). If the GL is in color index mode, each index that is read from this buffer is converted to a fixed-point format with an unspecified number of bits to the right of the binary point. Each index is then shifted left by GL_INDEX_SHIFT bits, and added to GL_INDEX_OFFSET. If GL_INDEX_SHIFT is negative, the shift is to the right. In either case, zero bits fill otherwise unspecified bit locations in the result. If GL_MAP_COLOR is true, the index is replaced with the value that it references in lookup table GL_PIXEL_MAP_I_TO_I. Whether the lookup replacement of the index is done or not, the integer part of the index is then ANDed with 2^b-1, where b is the number of bits in a color index buffer.

If the GL is in RGBA mode, the red, green, blue, and alpha components of each pixel that is read are converted to an internal floating-point format with unspecified precision. The conversion maps the largest representable component value to 1.0, and component value 0 to 0.0. The resulting floating-point color values are then multiplied by GL_c_SCALE and added to GL_c_BIAS, where c is RED, GREEN, BLUE, and ALPHA for the respective color components.

If GL_MAP_COLOR is true, each color component is clamped to the range [0,1] and scaled by the size of lookup table GL_PIXEL_MAP_c_TO_c, then replaced by the value that it references in that table. c is R, G, B, or A respectively.

If GL_COLOR_TABLE_EXT is true, each color component is clamped to the range [0,1] and scaled by the size of the GL_COLOR_TABLE_EXT, then replaced by the value that it references in that table according to the format of the color table (see glColorTableEXT).

If GL_CONVOLUTION_2D_EXT or GL_SEPARABLE_2D_EXT is true, two-dimensional convolution will be performed on each color component according to the format of the convolution filter (see glConvolutionFilter2DEXT and glSeparableFilter2DEXT).

If GL_POST_CONVOLUTION_COLOR_TABLE_EXT is true, each color component is clamped to the range [0,1] and scaled by the size of the GL_POST_CONVOLUTION_COLOR_TABLE_EXT, then replaced by the value that it references in that table according to the format of the color table (see glColorTableEXT).

Each color is then transformed by the color matrix (see glMatrixMode).

If GL_POST_COLOR_MATRIX_COLOR_TABLE_EXT is true, each color component is clamped to the range [0,1] and scaled by the size of the GL_POST_COLOR_MATRIX_COLOR_TABLE_EXT, then replaced by the value that it references in that table according to the format of the color table (see glColorTableEXT).

Each color is then clamped to the color clamp values (see glPixelTransfer).

The GL then converts the resulting indices or RGBA colors to fragments by attaching the current raster position z coordinate and texture coordinates to each pixel.

If GL_PIXEL_TEX_GEN_EXT, the image RGBA color is used as the texture coordinates for the fragment and the image color is replaced according to the pixel texture generation mode (see glPixelTexGenEXT).

Window coordinates x and y are assigned to the n^th fragment according to the following equations:

x_n = x_r + i
y_n = y_r + j

where (x_r, y_r) is the current raster position, and the pixel was the i^th pixel in the j^th row. If GL_INTERLACE_EXT is enabled, the y_n window coordinates is calculated as follows:

y_n = y_r + 2 * j

These pixel fragments are then treated just like the fragments generated by rasterizing points, lines, or polygons. Texture mapping, fog, and all the fragment operations are applied before the fragments are written to the frame buffer.

GL_DEPTH

Depth values are read from the depth buffer and converted directly to an internal floating-point format with unspecified precision. The resulting floating-point depth value is then multiplied by GL_DEPTH_SCALE and added to GL_DEPTH_BIAS. The result is clamped to the range [0,1].

The GL then converts the resulting depth components to fragments by attaching the current raster position color or color index and texture coordinates to each pixel, then assigning window coordinates (x_r + i, y_r + j), where (x_r, y_r) is the current raster position, and the pixel was the i^th pixel in the j^th row. These pixel fragments are then treated just like the fragments generated by rasterizing points, lines, or polygons. Texture mapping, fog, and all the fragment operations are applied before the fragments are written to the frame buffer.

GL_STENCIL

Stencil indices are read from the stencil buffer and converted to an internal fixed-point format with an unspecified number of bits to the right of the binary point. Each fixed-point index is then shifted left by GL_INDEX_SHIFT bits, and added to GL_INDEX_OFFSET. If GL_INDEX_SHIFT is negative, the shift is to the right. In either case, zero bits fill otherwise unspecified bit locations in the result. If GL_MAP_STENCIL is true, the index is replaced with the value that it references in lookup table GL_PIXEL_MAP_S_TO_S. Whether the lookup replacement of the index is done or not, the integer part of the index is then ANDed with 2^b-1, where b is the number of bits in the stencil buffer. The resulting stencil indices are then written to the stencil buffer such that the index read from the i^th location of the j^th row is written to location (x_r + i, y_r + j), where (x_r, y_r) is the current raster position. Only the pixel ownership test, the scissor test, and the stencil writemask affect these write operations.

(x_r + zoom_xi, y_r + zoom_yj)
and
(x_r + zoom_x(i+1), y_r + zoom_y(j+1))

where zoom_x is the value of GL_ZOOM_X and zoom_y is the value of GL_ZOOM_Y.

NOTES

EXTENSIONS

GL_I3D_color_clamp

The color clamp is part of the I3D_color_clamp extension.

GL_EXT_color_matrix

The color matrix is part of the EXT_color_matrix extension.

GL_EXT_color_table

GL_COLOR_TABLE_EXT, GL_POST_CONVOLUTION_COLOR_TABLE_EXT, and GL_POST_COLOR_MATRIX_COLOR_TABLE_EXT are part of the EXT_color_table extension.

GL_EXT_convolution

GL_CONVOLUTION_2D_EXT and GL_SEPARABLE_2D_EXT are part of the EXT_convolution extension.

EXT_interlace

GL_INTERLACE_EXT is part of the EXT_interlace extension.

EXT_interlace_read

GL_INTERLACE_READ_I3D is part of the EXT_interlace_read extension.

GL_EXT_pixel_texture

GL_PIXEL_TEX_GEN_EXT is part of the EXT_pixel_texture extension.

ERRORS

GL_INVALID_VALUE is generated if either width or height is negative.

GL_INVALID_OPERATION is generated if type is GL_DEPTH and there is no depth buffer.

GL_INVALID_OPERATION is generated if type is GL_STENCIL and there is no stencil buffer.

GL_INVALID_OPERATION is generated if glCopyPixels is executed between the execution of glBegin and the corresponding execution of glEnd.

ASSOCIATED GETS

SEE ALSO