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glCopyPixels(3G)
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glCopyPixels - copy pixels in the frame buffer
void glCopyPixels(
GLint x,
GLint y,
GLsizei width,
GLsizei height,
GLenum type );
Specify the window coordinates of the lower left corner of
the rectangular region of pixels to be copied. Specify
the dimensions of the rectangular region of pixels to be
copied. Both must be nonnegative. Specifies whether color
values, depth values, or stencil values are to be copied.
Symbolic constants GL_COLOR, GL_DEPTH, and GL_STENCIL are
accepted.
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: 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 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 with
unspecified precision. The conversion maps the
largest representable component value to 1.0, and
component value 0 to 0.0. The resulting floatingpoint
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 GL_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.
Depth values are read from the depth buffer and
converted directly to an internal floating-point
with unspecified precision. The resulting floatingpoint
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. Stencil indices are read from the
stencil buffer and converted to an internal fixedpoint
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 sup
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.
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);
Modes specified by glPixelStore() have no effect on the
operation of glCopyPixels().
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.
glGet() with argument GL_CURRENT_RASTER_POSITION
glGet() with argument GL_CURRENT_RASTER_POSITION_VALID
glColorTable(3), glConvolutionFilter1D(3), glConvolutionFilter2D(3), glDepthFunc(3), glDrawBuffer(3), glDrawPixels(3), glMatrixMode(3), glPixelMap(3), glPixelTransfer(3), glPixelZoom(3), glRasterPos(3), glReadBuffer(3),
glReadPixels(3), glSeparableFilter2D(3), glStencilFunc(3)
glCopyPixels(3G)
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