<div class="refentry" lang="en" xml:lang="en"><a id="glCopyPixels"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glCopyPixels — copy pixels in the frame buffer</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glCopyPixels</b>(</code></td><td>GLint  </td><td><var class="pdparam">x</var>, </td></tr><tr><td> </td><td>GLint  </td><td><var class="pdparam">y</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">width</var>, </td></tr><tr><td> </td><td>GLsizei  </td><td><var class="pdparam">height</var>, </td></tr><tr><td> </td><td>GLenum  </td><td><var class="pdparam">type</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>x</code></em>, </span><span class="term"><em class="parameter"><code>y</code></em></span></dt><dd><p>

Specify the window coordinates of the lower left corner

of the rectangular region of pixels to be copied.

</p></dd><dt><span class="term"><em class="parameter"><code>width</code></em>, </span><span class="term"><em class="parameter"><code>height</code></em></span></dt><dd><p>

Specify the dimensions of the rectangular region of pixels to be copied.

Both must be nonnegative.

</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>

Specifies whether color values,

depth values,

or stencil values are to be copied.

Symbolic constants

<code class="constant">GL_COLOR</code>,

<code class="constant">GL_DEPTH</code>,

and <code class="constant">GL_STENCIL</code> are accepted.

</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>

<code class="function">glCopyPixels</code> 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.

</p><p>

<em class="parameter"><code>x</code></em> and <em class="parameter"><code>y</code></em> specify the window coordinates of

the lower left corner of the rectangular region to be copied.

<em class="parameter"><code>width</code></em> and <em class="parameter"><code>height</code></em> specify the dimensions of the

rectangular region to be copied.

Both <em class="parameter"><code>width</code></em> and <em class="parameter"><code>height</code></em> must not be negative.

</p><p>

Several parameters control the processing of the pixel data

while it is being copied.

These parameters are set with three commands:

<a class="citerefentry" href="glPixelTransfer"><span class="citerefentry"><span class="refentrytitle">glPixelTransfer</span></span></a>,

<a class="citerefentry" href="glPixelMap"><span class="citerefentry"><span class="refentrytitle">glPixelMap</span></span></a>, and

<a class="citerefentry" href="glPixelZoom"><span class="citerefentry"><span class="refentrytitle">glPixelZoom</span></span></a>.

This reference page describes the effects on <code class="function">glCopyPixels</code> of most,

but not all, of the parameters specified by these three commands.

</p><p>

<code class="function">glCopyPixels</code> copies values from each pixel with the lower left-hand corner at

<math overflow="scroll">

<mfenced open="(" close=")">

<mrow>

<mi mathvariant="italic">x</mi>

<mo>+</mo>

<mi mathvariant="italic">i</mi>

</mrow>

<mrow>

<mi mathvariant="italic">y</mi>

<mo>+</mo>

<mi mathvariant="italic">j</mi>

</mrow>

</mfenced>

</math>

for

<math overflow="scroll">

<mrow>

<mn>0</mn>

<mo>&lt;=</mo>

<mi mathvariant="italic">i</mi>

<mo>&lt;</mo>

<mi mathvariant="italic">width</mi>

</mrow>

</math>

and

<math overflow="scroll">

<mrow>

<mn>0</mn>

<mo>&lt;=</mo>

<mi mathvariant="italic">j</mi>

<mo>&lt;</mo>

<mi mathvariant="italic">height</mi>

</mrow>

</math>.

This pixel is said to be the

<math overflow="scroll"><mi mathvariant="italic">i</mi></math>th

pixel in the

<math overflow="scroll"><mi mathvariant="italic">j</mi></math>th

row.

Pixels are copied in row order from the lowest to the highest row,

left to right in each row.

</p><p>

<em class="parameter"><code>type</code></em> specifies whether color, depth, or stencil data is to be copied.

The details of the transfer for each data type are as follows:

</p><div class="variablelist"><dl><dt><span class="term"><code class="constant">GL_COLOR</code></span></dt><dd><p>

Indices or RGBA colors are read from the buffer currently specified as the

read source buffer (see <a class="citerefentry" href="glReadBuffer"><span class="citerefentry"><span class="refentrytitle">glReadBuffer</span></span></a>).

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 <code class="constant">GL_INDEX_SHIFT</code> bits,

and added to <code class="constant">GL_INDEX_OFFSET</code>.

If <code class="constant">GL_INDEX_SHIFT</code> is negative,

the shift is to the right.

In either case, zero bits fill otherwise unspecified bit locations in the

result.

If <code class="constant">GL_MAP_COLOR</code> is true,

the index is replaced with the value that it references in lookup table

<code class="constant">GL_PIXEL_MAP_I_TO_I</code>.

Whether the lookup replacement of the index is done or not,

the integer part of the index is then ANDed with

<math overflow="scroll">

<mrow>

<msup><mn>2</mn>

<mi mathvariant="italic">b</mi>

</msup>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>,

where

<math overflow="scroll"><mi mathvariant="italic">b</mi></math>

is the number of bits in a color index buffer.

</p><p>

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 <code class="constant">GL_c_SCALE</code> and added to <code class="constant">GL_c_BIAS</code>,

where <span class="emphasis"><em>c</em></span> is RED, GREEN, BLUE, and ALPHA

for the respective color components.

The results are clamped to the range [0,1].

If <code class="constant">GL_MAP_COLOR</code> is true,

each color component is scaled by the size of lookup table

<code class="constant">GL_PIXEL_MAP_c_TO_c</code>,

then replaced by the value that it references in that table.

<span class="emphasis"><em>c</em></span> is R, G, B, or A.

</p><p>

If the <code class="code">ARB_imaging</code> extension is supported, the color values may

be

additionally processed by color-table lookups, color-matrix

transformations, and convolution filters.

</p><p>

The GL then converts the resulting indices or RGBA colors to fragments

by attaching the current raster position <span class="emphasis"><em>z</em></span> coordinate and

texture coordinates to each pixel,

then assigning window coordinates

<math overflow="scroll">

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mi mathvariant="italic">i</mi>

</mrow>

<mrow>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mi mathvariant="italic">j</mi>

</mrow>

</mfenced>

</math>,

where

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

</mfenced>

</math>

is the current raster position,

and the pixel was the

<math overflow="scroll"><mi mathvariant="italic">i</mi></math>th

pixel in the

<math overflow="scroll"><mi mathvariant="italic">j</mi></math>th

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.

</p></dd><dt><span class="term"><code class="constant">GL_DEPTH</code></span></dt><dd><p>

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 <code class="constant">GL_DEPTH_SCALE</code> and added to <code class="constant">GL_DEPTH_BIAS</code>.

The result is clamped to the range [0,1].

</p><p>

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

<math overflow="scroll">

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mi mathvariant="italic">i</mi>

</mrow>

<mrow>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mi mathvariant="italic">j</mi>

</mrow>

</mfenced>

</math>,

where

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

</mfenced>

</math>

is the current raster position,

and the pixel was the

<math overflow="scroll"><mi mathvariant="italic">i</mi></math>th

pixel in the

<math overflow="scroll"><mi mathvariant="italic">j</mi></math>th

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.

</p></dd><dt><span class="term"><code class="constant">GL_STENCIL</code></span></dt><dd><p>

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 <code class="constant">GL_INDEX_SHIFT</code> bits,

and added to <code class="constant">GL_INDEX_OFFSET</code>.

If <code class="constant">GL_INDEX_SHIFT</code> is negative,

the shift is to the right.

In either case, zero bits fill otherwise unspecified bit locations in the

result.

If <code class="constant">GL_MAP_STENCIL</code> is true,

the index is replaced with the value that it references in lookup table

<code class="constant">GL_PIXEL_MAP_S_TO_S</code>.

Whether the lookup replacement of the index is done or not,

the integer part of the index is then ANDed with

<math overflow="scroll">

<mrow>

<msup><mn>2</mn>

<mi mathvariant="italic">b</mi>

</msup>

<mo>-</mo>

<mn>1</mn>

</mrow>

</math>,

where

<math overflow="scroll"><mi mathvariant="italic">b</mi></math>

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

<math overflow="scroll"><mi mathvariant="italic">i</mi></math>th

location of the

<math overflow="scroll"><mi mathvariant="italic">j</mi></math>th

row

is written to location

<math overflow="scroll">

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mi mathvariant="italic">i</mi>

</mrow>

<mrow>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mi mathvariant="italic">j</mi>

</mrow>

</mfenced>

</math>,

where

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

</mfenced>

</math>

is the current raster position.

Only the pixel ownership test,

the scissor test,

and the stencil writemask affect these write operations.

</p></dd></dl></div><p>

The rasterization described thus far assumes pixel zoom factors of 1.0.

If

<a class="citerefentry" href="glPixelZoom"><span class="citerefentry"><span class="refentrytitle">glPixelZoom</span></span></a> is used to change the

<math overflow="scroll"><mi mathvariant="italic">x</mi></math>

and

<math overflow="scroll"><mi mathvariant="italic">y</mi></math>

pixel zoom factors,

pixels are converted to fragments as follows.

If

<math overflow="scroll">

<mfenced open="(" close=")">

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

</mfenced>

</math>

is the current raster position,

and a given pixel is in the

<math overflow="scroll"><mi mathvariant="italic">i</mi></math>th

location in the

<math overflow="scroll"><mi mathvariant="italic">j</mi></math>th

row of the source

pixel rectangle,

then fragments are generated for pixels whose centers are in the rectangle

with corners at

</p><p>

<math overflow="scroll">

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mfenced open="" close="">

<msub><mi mathvariant="italic">zoom</mi>

<mi mathvariant="italic">x</mi>

</msub>

</mfenced>

<mo>⁢</mo>

<mi mathvariant="italic">i</mi>

</mrow>

<mrow>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mfenced open="" close="">

<msub><mi mathvariant="italic">zoom</mi>

<mi mathvariant="italic">y</mi>

</msub>

</mfenced>

<mo>⁢</mo>

<mi mathvariant="italic">j</mi>

</mrow>

</mfenced>

</math>

</p><p>

and

</p><p>

<math overflow="scroll">

<mfenced open="(" close=")">

<mrow>

<msub><mi mathvariant="italic">x</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mrow>

<mfenced open="" close="">

<msub><mi mathvariant="italic">zoom</mi>

<mi mathvariant="italic">x</mi>

</msub>

</mfenced>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<mi mathvariant="italic">i</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</mfenced>

</mrow>

</mrow>

<mrow>

<msub><mi mathvariant="italic">y</mi>

<mi mathvariant="italic">r</mi>

</msub>

<mo>+</mo>

<mrow>

<mfenced open="" close="">

<msub><mi mathvariant="italic">zoom</mi>

<mi mathvariant="italic">y</mi>

</msub>

</mfenced>

<mo>⁡</mo>

<mfenced open="(" close=")">

<mrow>

<mi mathvariant="italic">j</mi>

<mo>+</mo>

<mn>1</mn>

</mrow>

</mfenced>

</mrow>

</mrow>

</mfenced>

</math>

</p><p>

where

<math overflow="scroll">

<msub><mi mathvariant="italic">zoom</mi>

<mi mathvariant="italic">x</mi>

</msub>

</math>

is the value of <code class="constant">GL_ZOOM_X</code> and

<math overflow="scroll">

<msub><mi mathvariant="italic">zoom</mi>

<mi mathvariant="italic">y</mi>

</msub>

</math>

is the value of <code class="constant">GL_ZOOM_Y</code>.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="examples"></a><h2>Examples</h2><p>

To copy the color pixel in the lower left corner of the window to the current raster position,

use

</p><p>

</p><pre class="programlisting">

glCopyPixels(0, 0, 1, 1, <code class="constant">GL_COLOR</code>);

</pre><p>

</p><p>

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>

Modes specified by <a class="citerefentry" href="glPixelStore"><span class="citerefentry"><span class="refentrytitle">glPixelStore</span></span></a> have no effect on the operation

of <code class="function">glCopyPixels</code>.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="errors"></a><h2>Errors</h2><p>

<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>type</code></em> is not an accepted value.

</p><p>

<code class="constant">GL_INVALID_VALUE</code> is generated if either <em class="parameter"><code>width</code></em> or <em class="parameter"><code>height</code></em> is negative.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>type</code></em> is <code class="constant">GL_DEPTH</code>

and there is no depth buffer.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>type</code></em> is <code class="constant">GL_STENCIL</code>

and there is no stencil buffer.

</p><p>

<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glCopyPixels</code>

is executed between the execution of <a class="citerefentry" href="glBegin"><span class="citerefentry"><span class="refentrytitle">glBegin</span></span></a>

and the corresponding execution of <a class="citerefentry" href="glEnd"><span class="citerefentry"><span class="refentrytitle">glEnd</span></span></a>.

</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="associatedgets"></a><h2>Associated Gets</h2><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_CURRENT_RASTER_POSITION</code>

</p><p>

<a class="citerefentry" href="glGet"><span class="citerefentry"><span class="refentrytitle">glGet</span></span></a> with argument <code class="constant">GL_CURRENT_RASTER_POSITION_VALID</code>

</p></div>

{$pipelinestall}{$examples}

<div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>

<a class="citerefentry" href="glColorTable"><span class="citerefentry"><span class="refentrytitle">glColorTable</span></span></a>,

<a class="citerefentry" href="glConvolutionFilter1D"><span class="citerefentry"><span class="refentrytitle">glConvolutionFilter1D</span></span></a>,

<a class="citerefentry" href="glConvolutionFilter2D"><span class="citerefentry"><span class="refentrytitle">glConvolutionFilter2D</span></span></a>,

<a class="citerefentry" href="glDepthFunc"><span class="citerefentry"><span class="refentrytitle">glDepthFunc</span></span></a>,

<a class="citerefentry" href="glDrawBuffer"><span class="citerefentry"><span class="refentrytitle">glDrawBuffer</span></span></a>,

<a class="citerefentry" href="glDrawPixels"><span class="citerefentry"><span class="refentrytitle">glDrawPixels</span></span></a>,

<a class="citerefentry" href="glMatrixMode"><span class="citerefentry"><span class="refentrytitle">glMatrixMode</span></span></a>,

<a class="citerefentry" href="glPixelMap"><span class="citerefentry"><span class="refentrytitle">glPixelMap</span></span></a>,

<a class="citerefentry" href="glPixelTransfer"><span class="citerefentry"><span class="refentrytitle">glPixelTransfer</span></span></a>,

<a class="citerefentry" href="glPixelZoom"><span class="citerefentry"><span class="refentrytitle">glPixelZoom</span></span></a>,

<a class="citerefentry" href="glRasterPos"><span class="citerefentry"><span class="refentrytitle">glRasterPos</span></span></a>,

<a class="citerefentry" href="glReadBuffer"><span class="citerefentry"><span class="refentrytitle">glReadBuffer</span></span></a>,

<a class="citerefentry" href="glReadPixels"><span class="citerefentry"><span class="refentrytitle">glReadPixels</span></span></a>,

<a class="citerefentry" href="glSeparableFilter2D"><span class="citerefentry"><span class="refentrytitle">glSeparableFilter2D</span></span></a>,

<a class="citerefentry" href="glStencilFunc"><span class="citerefentry"><span class="refentrytitle">glStencilFunc</span></span></a>,

<a class="citerefentry" href="glWindowPos"><span class="citerefentry"><span class="refentrytitle">glWindowPos</span></span></a>

</p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>

Copyright © 1991-2006

Silicon Graphics, Inc. This document is licensed under the SGI

Free Software B License. For details, see

<a class="ulink" href="https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/" target="_top">https://web.archive.org/web/20171022161616/http://oss.sgi.com/projects/FreeB/</a>.

</p></div></div></div>