GLCOPYPIXELS(3G)														  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  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 inter-
		      nal floating-point  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 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 colors to fragments by attaching the current raster position 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 frag-
		      ments 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 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 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 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 (xr
		      + i , yr + j), where (xr , yr) 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 (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 + zoomx*i, yr + zoomy*j)

									   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 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

																  GLCOPYPIXELS(3G)