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<div class="refentry" lang="en" xml:lang="en"><a id="glConvolutionFilter2D"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>glConvolutionFilter2D — define a two-dimensional convolution filter</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">glConvolutionFilter2D</b>(</code></td><td>GLenum </td><td><var class="pdparam">target</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">internalformat</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">format</var>, </td></tr><tr><td> </td><td>GLenum </td><td><var class="pdparam">type</var>, </td></tr><tr><td> </td><td>const GLvoid * </td><td><var class="pdparam">data</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>target</code></em></span></dt><dd><p>
Must be <code class="constant">GL_CONVOLUTION_2D</code>.
</p></dd><dt><span class="term"><em class="parameter"><code>internalformat</code></em></span></dt><dd><p>
The internal format of the convolution filter kernel.
The allowable values are
<code class="constant">GL_ALPHA</code>,
<code class="constant">GL_ALPHA4</code>,
<code class="constant">GL_ALPHA8</code>,
<code class="constant">GL_ALPHA12</code>,
<code class="constant">GL_ALPHA16</code>,
<code class="constant">GL_LUMINANCE</code>,
<code class="constant">GL_LUMINANCE4</code>,
<code class="constant">GL_LUMINANCE8</code>,
<code class="constant">GL_LUMINANCE12</code>,
<code class="constant">GL_LUMINANCE16</code>,
<code class="constant">GL_LUMINANCE_ALPHA</code>,
<code class="constant">GL_LUMINANCE4_ALPHA4</code>,
<code class="constant">GL_LUMINANCE6_ALPHA2</code>,
<code class="constant">GL_LUMINANCE8_ALPHA8</code>,
<code class="constant">GL_LUMINANCE12_ALPHA4</code>,
<code class="constant">GL_LUMINANCE12_ALPHA12</code>,
<code class="constant">GL_LUMINANCE16_ALPHA16</code>,
<code class="constant">GL_INTENSITY</code>,
<code class="constant">GL_INTENSITY4</code>,
<code class="constant">GL_INTENSITY8</code>,
<code class="constant">GL_INTENSITY12</code>,
<code class="constant">GL_INTENSITY16</code>,
<code class="constant">GL_R3_G3_B2</code>,
<code class="constant">GL_RGB</code>,
<code class="constant">GL_RGB4</code>,
<code class="constant">GL_RGB5</code>,
<code class="constant">GL_RGB8</code>,
<code class="constant">GL_RGB10</code>,
<code class="constant">GL_RGB12</code>,
<code class="constant">GL_RGB16</code>,
<code class="constant">GL_RGBA</code>,
<code class="constant">GL_RGBA2</code>,
<code class="constant">GL_RGBA4</code>,
<code class="constant">GL_RGB5_A1</code>,
<code class="constant">GL_RGBA8</code>,
<code class="constant">GL_RGB10_A2</code>,
<code class="constant">GL_RGBA12</code>, or
<code class="constant">GL_RGBA16</code>.
</p></dd><dt><span class="term"><em class="parameter"><code>width</code></em></span></dt><dd><p>
The width of the pixel array referenced by <em class="parameter"><code>data</code></em>.
</p></dd><dt><span class="term"><em class="parameter"><code>height</code></em></span></dt><dd><p>
The height of the pixel array referenced by <em class="parameter"><code>data</code></em>.
</p></dd><dt><span class="term"><em class="parameter"><code>format</code></em></span></dt><dd><p>
The format of the pixel data in <em class="parameter"><code>data</code></em>.
The allowable values are
<code class="constant">GL_RED</code>,
<code class="constant">GL_GREEN</code>,
<code class="constant">GL_BLUE</code>,
<code class="constant">GL_ALPHA</code>,
<code class="constant">GL_RGB</code>,
<code class="constant">GL_BGR</code>,
<code class="constant">GL_RGBA</code>,
<code class="constant">GL_BGRA</code>,
<code class="constant">GL_LUMINANCE</code>, and
<code class="constant">GL_LUMINANCE_ALPHA</code>.
</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>
The type of the pixel data in <em class="parameter"><code>data</code></em>.
Symbolic constants
<code class="constant">GL_UNSIGNED_BYTE</code>,
<code class="constant">GL_BYTE</code>,
<code class="constant">GL_BITMAP</code>,
<code class="constant">GL_UNSIGNED_SHORT</code>,
<code class="constant">GL_SHORT</code>,
<code class="constant">GL_UNSIGNED_INT</code>,
<code class="constant">GL_INT</code>,
<code class="constant">GL_FLOAT</code>,
<code class="constant">GL_UNSIGNED_BYTE_3_3_2</code>,
<code class="constant">GL_UNSIGNED_BYTE_2_3_3_REV</code>,
<code class="constant">GL_UNSIGNED_SHORT_5_6_5</code>,
<code class="constant">GL_UNSIGNED_SHORT_5_6_5_REV</code>,
<code class="constant">GL_UNSIGNED_SHORT_4_4_4_4</code>,
<code class="constant">GL_UNSIGNED_SHORT_4_4_4_4_REV</code>,
<code class="constant">GL_UNSIGNED_SHORT_5_5_5_1</code>,
<code class="constant">GL_UNSIGNED_SHORT_1_5_5_5_REV</code>,
<code class="constant">GL_UNSIGNED_INT_8_8_8_8</code>,
<code class="constant">GL_UNSIGNED_INT_8_8_8_8_REV</code>,
<code class="constant">GL_UNSIGNED_INT_10_10_10_2</code>, and
<code class="constant">GL_UNSIGNED_INT_2_10_10_10_REV</code>
are accepted.
</p></dd><dt><span class="term"><em class="parameter"><code>data</code></em></span></dt><dd><p>
Pointer to a two-dimensional array of pixel data that is processed to
build the convolution filter kernel.
</p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
<code class="function">glConvolutionFilter2D</code> builds a two-dimensional convolution filter kernel from an array of
pixels.
</p><p>
The pixel array specified by <em class="parameter"><code>width</code></em>, <em class="parameter"><code>height</code></em>, <em class="parameter"><code>format</code></em>, <em class="parameter"><code>type</code></em>, and
<em class="parameter"><code>data</code></em> is extracted from memory and processed just as if
<a class="citerefentry" href="glDrawPixels"><span class="citerefentry"><span class="refentrytitle">glDrawPixels</span></span></a> were called, but processing stops after the final
expansion to RGBA is completed.
</p><p>
If a non-zero named buffer object is bound to the <code class="constant">GL_PIXEL_UNPACK_BUFFER</code> target
(see <a class="citerefentry" href="glBindBuffer"><span class="citerefentry"><span class="refentrytitle">glBindBuffer</span></span></a>) while a convolution filter is
specified, <em class="parameter"><code>data</code></em> is treated as a byte offset into the buffer object's data store.
</p><p>
The R, G, B, and A components of each pixel are next scaled by the four
2D <code class="constant">GL_CONVOLUTION_FILTER_SCALE</code> parameters and biased by the
four 2D <code class="constant">GL_CONVOLUTION_FILTER_BIAS</code> parameters.
(The scale and bias parameters are set by <a class="citerefentry" href="glConvolutionParameter"><span class="citerefentry"><span class="refentrytitle">glConvolutionParameter</span></span></a>
using the <code class="constant">GL_CONVOLUTION_2D</code> target and the names
<code class="constant">GL_CONVOLUTION_FILTER_SCALE</code> and <code class="constant">GL_CONVOLUTION_FILTER_BIAS</code>.
The parameters themselves are vectors of four values that are applied to red,
green, blue, and alpha, in that order.)
The R, G, B, and A values are not clamped to [0,1] at any time during this
process.
</p><p>
Each pixel is then converted to the internal format specified by
<em class="parameter"><code>internalformat</code></em>.
This conversion simply maps the component values of the pixel (R, G, B,
and A) to the values included in the internal format (red, green, blue,
alpha, luminance, and intensity). The mapping is as follows:
</p><p>
</p><div class="informaltable"><table><colgroup><col /><col /><col /><col /><col /><col /><col /></colgroup><thead><tr><th><span class="bold"><strong>
Internal Format
</strong></span></th><th class="center"><span class="bold"><strong>
Red
</strong></span></th><th class="center"><span class="bold"><strong>
Green
</strong></span></th><th class="center"><span class="bold"><strong>
Blue
</strong></span></th><th class="center"><span class="bold"><strong>
Alpha
</strong></span></th><th class="center"><span class="bold"><strong>
Luminance
</strong></span></th><th class="center"><span class="bold"><strong>
Intensity
</strong></span></th></tr></thead><tbody><tr><td>
<code class="constant">GL_ALPHA</code>
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
A
</td><td class="center">
</td><td class="center">
</td></tr><tr><td>
<code class="constant">GL_LUMINANCE</code>
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
R
</td><td class="center">
</td></tr><tr><td>
<code class="constant">GL_LUMINANCE_ALPHA</code>
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
A
</td><td class="center">
R
</td><td class="center">
</td></tr><tr><td>
<code class="constant">GL_INTENSITY</code>
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td><td class="center">
R
</td></tr><tr><td>
<code class="constant">GL_RGB</code>
</td><td class="center">
R
</td><td class="center">
G
</td><td class="center">
B
</td><td class="center">
</td><td class="center">
</td><td class="center">
</td></tr><tr><td>
<code class="constant">GL_RGBA</code>
</td><td class="center">
R
</td><td class="center">
G
</td><td class="center">
B
</td><td class="center">
A
</td><td class="center">
</td><td class="center">
</td></tr></tbody></table></div><p>
The red, green, blue, alpha, luminance, and/or intensity components of
the resulting pixels are stored in floating-point rather than integer
format.
They form a two-dimensional filter kernel image indexed with coordinates
<span class="emphasis"><em>i</em></span> and <span class="emphasis"><em>j</em></span> such that <span class="emphasis"><em>i</em></span> starts at zero and increases from left
to right, and <span class="emphasis"><em>j</em></span> starts at zero and increases from bottom to top.
Kernel location <span class="emphasis"><em>i,j</em></span> is derived from the <span class="emphasis"><em>N</em></span>th pixel,
where <span class="emphasis"><em>N</em></span> is <span class="emphasis"><em>i</em></span>+<span class="emphasis"><em>j</em></span>*<em class="parameter"><code>width</code></em>.
</p><p>
Note that after a convolution is performed, the resulting color
components are also scaled by their corresponding
<code class="constant">GL_POST_CONVOLUTION_c_SCALE</code> parameters and biased by their
corresponding <code class="constant">GL_POST_CONVOLUTION_c_BIAS</code> parameters (where
<span class="emphasis"><em>c</em></span> takes on the values <span class="bold"><strong>RED</strong></span>, <span class="bold"><strong>GREEN</strong></span>, <span class="bold"><strong>BLUE</strong></span>, and
<span class="bold"><strong>ALPHA</strong></span>).
These parameters are set by <a class="citerefentry" href="glPixelTransfer"><span class="citerefentry"><span class="refentrytitle">glPixelTransfer</span></span></a>.
</p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
<code class="function">glConvolutionFilter2D</code> is present only if <code class="code">ARB_imaging</code> is returned when <a class="citerefentry" href="glGetString"><span class="citerefentry"><span class="refentrytitle">glGetString</span></span></a>
is called with an argument of <code class="constant">GL_EXTENSIONS</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>target</code></em> is not
<code class="constant">GL_CONVOLUTION_2D</code>.
</p><p>
<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>internalformat</code></em> is not one of the
allowable values.
</p><p>
<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>format</code></em> is not one of the allowable
values.
</p><p>
<code class="constant">GL_INVALID_ENUM</code> is generated if <em class="parameter"><code>type</code></em> is not one of the allowable
values.
</p><p>
<code class="constant">GL_INVALID_VALUE</code> is generated if <em class="parameter"><code>width</code></em> is less than zero or greater
than the maximum supported value.
This value may be queried with <a class="citerefentry" href="glGetConvolutionParameter"><span class="citerefentry"><span class="refentrytitle">glGetConvolutionParameter</span></span></a>
using target <code class="constant">GL_CONVOLUTION_2D</code> and name
<code class="constant">GL_MAX_CONVOLUTION_WIDTH</code>.
</p><p>
<code class="constant">GL_INVALID_VALUE</code> is generated if <em class="parameter"><code>height</code></em> is less than zero or greater
than the maximum supported value.
This value may be queried with <a class="citerefentry" href="glGetConvolutionParameter"><span class="citerefentry"><span class="refentrytitle">glGetConvolutionParameter</span></span></a>
using target <code class="constant">GL_CONVOLUTION_2D</code> and name
<code class="constant">GL_MAX_CONVOLUTION_HEIGHT</code>.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>height</code></em> is one of
<code class="constant">GL_UNSIGNED_BYTE_3_3_2</code>,
<code class="constant">GL_UNSIGNED_BYTE_2_3_3_REV</code>,
<code class="constant">GL_UNSIGNED_SHORT_5_6_5</code>, or
<code class="constant">GL_UNSIGNED_SHORT_5_6_5_REV</code>
and <em class="parameter"><code>format</code></em> is not <code class="constant">GL_RGB</code>.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if <em class="parameter"><code>height</code></em> is one of
<code class="constant">GL_UNSIGNED_SHORT_4_4_4_4</code>,
<code class="constant">GL_UNSIGNED_SHORT_4_4_4_4_REV</code>,
<code class="constant">GL_UNSIGNED_SHORT_5_5_5_1</code>,
<code class="constant">GL_UNSIGNED_SHORT_1_5_5_5_REV</code>,
<code class="constant">GL_UNSIGNED_INT_8_8_8_8</code>,
<code class="constant">GL_UNSIGNED_INT_8_8_8_8_REV</code>,
<code class="constant">GL_UNSIGNED_INT_10_10_10_2</code>, or
<code class="constant">GL_UNSIGNED_INT_2_10_10_10_REV</code>
and <em class="parameter"><code>format</code></em> is neither <code class="constant">GL_RGBA</code> nor <code class="constant">GL_BGRA</code>.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if a non-zero buffer object name is bound to the
<code class="constant">GL_PIXEL_UNPACK_BUFFER</code> target and the buffer object's data store is currently mapped.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if a non-zero buffer object name is bound to the
<code class="constant">GL_PIXEL_UNPACK_BUFFER</code> target and the data would be unpacked from the buffer
object such that the memory reads required would exceed the data store size.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if a non-zero buffer object name is bound to the
<code class="constant">GL_PIXEL_UNPACK_BUFFER</code> target and <em class="parameter"><code>data</code></em> is not evenly divisible
into the number of bytes needed to store in memory a datum indicated by <em class="parameter"><code>type</code></em>.
</p><p>
<code class="constant">GL_INVALID_OPERATION</code> is generated if <code class="function">glConvolutionFilter2D</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="glGetConvolutionParameter"><span class="citerefentry"><span class="refentrytitle">glGetConvolutionParameter</span></span></a>, <a class="citerefentry" href="glGetConvolutionFilter"><span class="citerefentry"><span class="refentrytitle">glGetConvolutionFilter</span></span></a>
</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="glConvolutionFilter1D"><span class="citerefentry"><span class="refentrytitle">glConvolutionFilter1D</span></span></a>,
<a class="citerefentry" href="glSeparableFilter2D"><span class="citerefentry"><span class="refentrytitle">glSeparableFilter2D</span></span></a>,
<a class="citerefentry" href="glConvolutionParameter"><span class="citerefentry"><span class="refentrytitle">glConvolutionParameter</span></span></a>,
<a class="citerefentry" href="glPixelTransfer"><span class="citerefentry"><span class="refentrytitle">glPixelTransfer</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>