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GLCOPYPIXELS(3G)			  OpenGL Manual 			 GLCOPYPIXELS(3G)

NAME
       glCopyPixels - copy pixels in the frame buffer

C SPECIFICATION
       void glCopyPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum type);

PARAMETERS
       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.

DESCRIPTION
       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, the integer part of the index is then ANDed with 2 b - 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 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 x r + i y r + j, where x r y r 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
	   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 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 r + i y r + j, where x r y r 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
	   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 the index is then ANDed with 2 b - 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 r + i y r + j, where x r y r is the current raster position.
	   Only the 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 glPixelZoom()
       is used to change the x and y pixel zoom factors, pixels are converted to fragments as
       follows. If x r y r 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

       x r + zoom x  i y r + zoom y  j

       and

       x r + zoom x  i + 1 y r + zoom y  j + 1

       where zoom x is the value of GL_ZOOM_X and zoom y 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 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().

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(), glWindowPos()

COPYRIGHT
       Copyright (C) 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/.

AUTHORS
       opengl.org

opengl.org				    06/10/2014				 GLCOPYPIXELS(3G)
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