OpenGL man pages
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 (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:
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,
b
the integer part of the index is then ANDed with 2 -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 zero 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,
respectively.
The resulting indices or RGBA colors are then converted to
fragments by attaching the current raster position z
coordinate and texture coordinates to each pixel, then
assigning window coordinates (x +i,y +j), where (x ,y ) is
r r r r
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.
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 resulting depth components are then converted 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
r r r r
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.
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
b
the index is then ANDed with 2 -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 raster
r r r r
position. Only the pixel ownership test, the scissor test,
and the stencil writemask affect these writes.
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 , y ) is the current raster
r r
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 +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 GL_ZOOM_X and zoom is the value of GL_ZOOM_Y.
x 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
glDepthFunc, glDrawBuffer, glDrawPixels, glPixelMap, glPixelTransfer, glPixelZoom, glRasterPos, glReadBuffer, glReadPixels, glStencilFunc
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Last Edited:
Fri Dec 6 11:18:03 EST 1996
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