glCopyPixels man page on Oracle

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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 © 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			  04/29/2014		      GLCOPYPIXELS(3G)
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