C SPECIFICATION
void GLAPIENTRY glCopyPixels( GLint x,
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 val-
ues 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 spec-
ified 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 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
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, 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 cur-
rently 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
ified precision. The conversion maps the largest repre-
sentable 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 respec-
tive color components. The results are clamped to the
range [0,1]. If GL_MAP_COLOR is true, each color compo-
nent 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 col-
ors to fragments by attaching the current raster posi-
tion 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 map-
ping, 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 con-
verted 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 (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 map-
ping, 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
If
glPixelZoom is used to change the x and y pixel zoom factors, pixels
are converted to fragments as follows. If (xr, yr) 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
(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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