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<STRONG>NAME</STRONG>
<STRONG>glCopyPixels</STRONG> - copy pixels in the frame buffer
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glCopyPixels</STRONG>( GLint <EM>x</EM>,
GLint <EM>y</EM>,
GLsizei <EM>width</EM>,
GLsizei <EM>height</EM>,
GLenum <EM>type</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>x</EM>, <EM>y</EM> Specify the window coordinates of the lower left corner
of the rectangular region of pixels to be copied.
<EM>width</EM>, <EM>height</EM>
Specify the dimensions of the rectangular region of
pixels to be copied. Both must be nonnegative.
<EM>type</EM> Specifies whether color values, depth values, or
stencil values are to be copied. Symbolic constants
<STRONG>GL_COLOR</STRONG>, <STRONG>GL_DEPTH</STRONG>, and <STRONG>GL_STENCIL</STRONG> are accepted.
<STRONG>DESCRIPTION</STRONG>
<STRONG>glCopyPixels</STRONG> 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.
<EM>x</EM> and <EM>y</EM> specify the window coordinates of the lower left
corner of the rectangular region to be copied. <EM>width</EM> and
<EM>height</EM> specify the dimensions of the rectangular region to
be copied. Both <EM>width</EM> and <EM>height</EM> 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: <STRONG>glPixelTransfer</STRONG>, <STRONG>glPixelMap</STRONG>, and
<STRONG>glPixelZoom</STRONG>. This reference page describes the effects on
<STRONG>glCopyPixels</STRONG> of most, but not all, of the parameters
specified by these three commands.
<STRONG>glCopyPixels</STRONG> copies values from each pixel with the lower
left-hand corner at (<EM>x</EM> + i, <EM>y</EM> + j) for 0<EM><</EM>i<<EM>width</EM> and
0<EM><</EM>j<<EM>height</EM>. 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.
<EM>type</EM> specifies whether color, depth, or stencil data is to
be copied. The details of the transfer for each data type
are as follows:
<STRONG>GL_COLOR</STRONG> Indices or RGBA colors are read from the
buffer currently specified as the read source
buffer (see <STRONG>glReadBuffer</STRONG>). 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 <STRONG>GL_INDEX_SHIFT</STRONG>
bits, and added to <STRONG>GL_INDEX_OFFSET</STRONG>. If
<STRONG>GL_INDEX_SHIFT</STRONG> is negative, the shift is to
the right. In either case, zero bits fill
otherwise unspecified bit locations in the
result. If <STRONG>GL_MAP_COLOR</STRONG> is true, the index
is replaced with the value that it references
in lookup table <STRONG>GL_PIXEL_MAP_I_TO_I</STRONG>. Whether
the lookup replacement of the index is done
or not, the integer part of the index is then
ANDed with 2b-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 <STRONG>GL_c_SCALE</STRONG> and added to
<STRONG>GL_c_BIAS</STRONG>, where <EM>c</EM> is RED, GREEN, BLUE, and
ALPHA for the respective color components.
The results are clamped to the range [0,1].
If <STRONG>GL_MAP_COLOR</STRONG> is true, each color component
is scaled by the size of lookup table
<STRONG>GL_PIXEL_MAP_c_TO_c</STRONG>, then replaced by the
value that it references in that table. <EM>c</EM> is
R, G, B, or A.
The GL then converts the resulting indices or
RGBA colors to fragments by attaching the
current raster position <EM>z</EM> coordinate and
texture coordinates to each pixel, then
assigning window coordinates (x +i,y +j),
where (x ,y ) is the current ra<STRONG>s</STRONG>ter <STRONG>p</STRONG>osition,
and the <STRONG>p</STRONG>ix<STRONG>e</STRONG>l 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.
<STRONG>GL_DEPTH</STRONG> 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
<STRONG>GL_DEPTH_SCALE</STRONG> and added to <STRONG>GL_DEPTH_BIAS</STRONG>.
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 +i,y +j),
where (x ,y ) is the current ra<STRONG>s</STRONG>ter <STRONG>p</STRONG>osition,
and the <STRONG>p</STRONG>ix<STRONG>e</STRONG>l 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.
<STRONG>GL_STENCIL</STRONG> 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
<STRONG>GL_INDEX_SHIFT</STRONG> bits, and added to
<STRONG>GL_INDEX_OFFSET</STRONG>. If <STRONG>GL_INDEX_SHIFT</STRONG> is
negative, the shift is to the right. In
either case, zero bits fill otherwise
unspecified bit locations in the result. If
<STRONG>GL_MAP_STENCIL</STRONG> is true, the index is replaced
with the value that it references in lookup
table <STRONG>GL_PIXEL_MAP_S_TO_S</STRONG>. Whether the
lookup replacement of the index is done or
not, the integer part of the index is then
ANDed with 2b-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 +i,y +j), where (x ,y ) is the
current ras<STRONG>t</STRONG>er p<STRONG>o</STRONG>sition. Onlyrth<STRONG>e</STRONG> 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
<STRONG>glPixelZoom</STRONG> is used to change the x and y pixel zoom
factors, pixels are converted to fragments as follows. If
(x , y ) is the current raster position, and a given pixel
isrin <STRONG>t</STRONG>he 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 +zoom i, y +zoom j)
r x r y
and
(x +zoom (i+1), y +zoom (j+1))
r x r y
where zoom is the value of <STRONG>GL_ZOOM_X</STRONG> and zoom is the value
of <STRONG>GL_ZOOM_Y</STRONG>. y
<STRONG>EXAMPLES</STRONG>
To copy the color pixel in the lower left corner of the
window to the current raster position, use glCopyPixels(0,
0, 1, 1, <STRONG>GL_COLOR</STRONG>);
<STRONG>NOTES</STRONG>
Modes specified by <STRONG>glPixelStore</STRONG> have no effect on the
operation of <STRONG>glCopyPixels</STRONG>.
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>type</EM> is not an accepted
value.
<STRONG>GL_INVALID_VALUE</STRONG> is generated if either <EM>width</EM> or <EM>height</EM> is
negative.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <EM>type</EM> is <STRONG>GL_DEPTH</STRONG> and
there is no depth buffer.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <EM>type</EM> is <STRONG>GL_STENCIL</STRONG> and
there is no stencil buffer.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glCopyPixels</STRONG> is
executed between the execution of <STRONG>glBegin</STRONG> and the
corresponding execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_CURRENT_RASTER_POSITION</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_CURRENT_RASTER_POSITION_VALID</STRONG>
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glDepthFunc</STRONG>, <STRONG>glDrawBuffer</STRONG>, <STRONG>glDrawPixels</STRONG>, <STRONG>glPixelMap</STRONG>,
<STRONG>glPixelTransfer</STRONG>, <STRONG>glPixelZoom</STRONG>, <STRONG>glRasterPos</STRONG>, <STRONG>glReadBuffer</STRONG>,
<STRONG>glReadPixels</STRONG>, <STRONG>glStencilFunc</STRONG>
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