glCopyPixels — copy pixels in the frame buffer
void glCopyPixels( | GLint | x, |
GLint | y, | |
GLsizei | width, | |
GLsizei | height, | |
GLenum | type) ; |
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.
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
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
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
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
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
The rasterization described thus far assumes pixel zoom factors of 1.0.
If
glPixelZoom is used to change the
and
where
GL_ZOOM_X
and
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
);
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, glConvolutionFilter1D, glConvolutionFilter2D, glDepthFunc, glDrawBuffer, glDrawPixels, glMatrixMode, glPixelMap, glPixelTransfer, glPixelZoom, glRasterPos, glReadBuffer, glReadPixels, glSeparableFilter2D, glStencilFunc, glWindowPos
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/.