glCopyPixels man page on RedHat
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GLCOPYPIXELS(3G) OpenGL Manual GLCOPYPIXELS(3G)
NAME
glCopyPixels - copy pixels in the frame buffer
C SPECIFICATION
void glCopyPixels(GLint x, GLint y, GLsizei width, GLsizei height,
GLenum type);
PARAMETERS
x, y
Specify the window coordinates of the lower left corner of the
rectangular region of pixels to be copied.
width, height
Specify the dimensions of the rectangular region of pixels to be
copied. Both must be nonnegative.
type
Specifies whether color values, depth values, or stencil values are
to be copied. Symbolic constants GL_COLOR, GL_DEPTH, and GL_STENCIL
are accepted.
DESCRIPTION
glCopyPixels copies a screen-aligned rectangle of pixels from the
specified frame buffer location to a region relative to the current
raster position. Its operation is well defined only if the entire pixel
source region is within the exposed portion of the window. Results of
copies from outside the window, or from regions of the window that are
not exposed, are hardware dependent and undefined.
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 glCopyPixels of most, but not all, of the
parameters specified by these three commands.
glCopyPixels copies values from each pixel with the lower left-hand
corner at x + i y + j for 0 <= i < width and 0 <= j < height. This
pixel is said to be the ith pixel in the jth row. Pixels are copied in
row order from the lowest to the highest row, left to right in each
row.
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.
The results are clamped to the range [0,1]. If GL_MAP_COLOR is
true, each color component is 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.
If the ARB_imaging extension is supported, the color values may be
additionally processed by color-table lookups, color-matrix
transformations, and convolution filters.
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, 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 ith pixel in the jth 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_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 ith pixel in the jth 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 ith location of the jth 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.
The rasterization described thus far assumes pixel zoom factors of 1.0.
If glPixelZoom() is used to change the x and y pixel zoom factors,
pixels are converted to fragments as follows. If x r y r is the current
raster position, and a given pixel is in the ith location in the jth
row of the source pixel rectangle, then fragments are generated for
pixels whose centers are in the rectangle with corners at
x r + zoom x i y r + zoom y j
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.
EXAMPLES
To copy the color pixel in the lower left corner of the window to the
current raster position, use
glCopyPixels(0, 0, 1, 1, GL_COLOR);
NOTES
Modes specified by glPixelStore() have no effect on the operation of
glCopyPixels.
ERRORS
GL_INVALID_ENUM is generated if type is not an accepted value.
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
glGet() with argument GL_CURRENT_RASTER_POSITION
glGet() with argument GL_CURRENT_RASTER_POSITION_VALID
SEE ALSO
glColorTable(), glConvolutionFilter1D(), glConvolutionFilter2D(),
glDepthFunc(), glDrawBuffer(), glDrawPixels(), glMatrixMode(),
glPixelMap(), glPixelTransfer(), glPixelZoom(), glRasterPos(),
glReadBuffer(), glReadPixels(), glSeparableFilter2D(), glStencilFunc(),
glWindowPos()
COPYRIGHT
Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
under the SGI Free Software B License. For details, see
http://oss.sgi.com/projects/FreeB/.
AUTHORS
opengl.org
opengl.org 03/16/2013 GLCOPYPIXELS(3G)
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