gl.CopyPixels(x, y, width, height, type)
gl.CopyPixels()
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: gl.PixelTransfer(), gl.PixelMap(),
and gl.PixelZoom(). This reference page describes the effects on gl.CopyPixels()
of
most, but not all, of the parameters specified by these three commands.
gl.CopyPixels()
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
#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 (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_DEPTH
#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
#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 gl.PixelZoom() 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
.
Modes specified by gl.PixelStore() have no effect on the operation of the command gl.CopyPixels()
.
Please consult an OpenGL reference manual for more information.
#GL_COLOR
, #GL_DEPTH
, and #GL_STENCIL
are accepted#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 gl.CopyPixels()
is executed between the execution of gl.Begin() and the corresponding execution of gl.End()
#GL_CURRENT_RASTER_POSITION
gl.Get() with argument #GL_CURRENT_RASTER_POSITION_VALID