GLint GLint )
PARAMETERS
x, GLint Specify the window coordinates of the lower left corner of the
rectangular region of pixels to be copied.
_param3, _param4
Specify the dimensions of the rectangular region of pixels to
be copied. Both must be nonnegative.
_param5 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 speci‐
fied 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 ex‐
posed, are hardware dependent and undefined.
x and GLint specify the window coordinates of the lower left corner of
the rectangular region to be copied. _param3 and _param4 specify the
dimensions of the rectangular region to be copied. Both _param3 and
_param4 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 de‐
scribes the effects on glCopyPixels of most, but not all, of the parame‐
ters specified by these three commands.
glCopyPixels copies values from each pixel with the lower left-hand cor‐
ner at (x + i, GLint + j) for 0 ≤ i < _param3 and 0 ≤ j < _param4. 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.
_param5 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
GL_MAP_COLOR is true, each color component is scaled by
the size of lookup table GL_PIXEL_MAP_c_TO_c, then re‐
placed 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 (xr+i,yr+j), where (xr,yr)
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 frag‐
ments 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 un‐
specified 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 (xr+i,yr+j), where
(xr,yr) 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 raster‐
izing 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 con‐
verted to an internal fixed-point format with an unspeci‐
fied 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 re‐
placement of the index is done or not, the integer part
of the index is then ANDed with 2b−1, where b is the num‐
ber of bits in the stencil buffer. The resulting stencil
indices are then written to the stencil buffer such that
(xr+zoomxi, yr+zoomyj)
and
(xr+zoomx(i+1), yr+zoomy(j+1))
where zoomx is the value of GL_ZOOM_X and zoomy 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 _param5 is not an accepted value.
GL_INVALID_VALUE is generated if either _param3 or _param4 is negative.
GL_INVALID_OPERATION is generated if _param5 is GL_DEPTH and there is no
depth buffer.
GL_INVALID_OPERATION is generated if _param5 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
GLCOPYPIXELS(3G)
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