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    <title>sampler_t</title>
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      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="sampler_t"></a>
        <h1> sampler_t</h1>
        <p>
            A type used to control how elements of a 2D or 3D image object are read by <code xmlns="http://www.w3.org/1999/xhtml" class="function">read_image{f|i|ui}</code>.
        </p>
      </div>
      <div class="refsect2">
        <a id="synopsis"></a>
        <h3>
        </h3>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
const sampler_t &lt;sampler name&gt; = &lt;value&gt;
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
The image read functions take a sampler argument. The sampler can be passed as an argument
to the kernel using <a class="citerefentry" href="clSetKernelArg.html"><span class="citerefentry"><span class="refentrytitle">clSetKernelArg</span></span></a>, or it can be a constant variable of type <span class="type">sampler_t</span> declared in the program source.
        </p>
        <p>
Sampler variables in a program are declared to be of type <span class="type">sampler_t</span>.
The <span class="type">sampler_t</span> type is a 32-bit unsigned int constant and is interpreted as a bit-field that specifies the following properties:
        </p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem">
              <p>
            Addressing Mode
       </p>
            </li>
            <li class="listitem">
              <p>
            Filter Mode
       </p>
            </li>
            <li class="listitem">
              <p>
           Normalized Coordinates
       </p>
            </li>
          </ul>
        </div>
        <p>
These properties control how elements of an image object are read by
<a class="citerefentry" href="imageFunctions.html"><span class="citerefentry"><span class="refentrytitle">read_image{f|i|ui}</span></span></a>.
        </p>
        <p>
Samplers can also be declared as global constants in the program source using the syntax shown at the top of this page.
        </p>
        <p>
The sampler fields are described in the table below:
        </p>
        <p>
        </p>
        <div class="informaltable">
          <table border="1">
            <colgroup>
              <col align="left" class="col1" />
              <col align="left" class="col2" />
            </colgroup>
            <thead>
              <tr>
                <th align="left">Sampler State</th>
                <th align="left">Description</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td align="left">
<p>
<code class="constant">&lt;normalized coords&gt;</code>
</p>
                        </td>
                <td align="left">
<p>
Specifies whether the <code class="varname">x</code>, <code class="varname">y</code> and <code class="varname">z</code> coordinates are passed in as normalized or unnormalized values. This must be a literal value and can be one of the following predefined enums:
</p>

<p>
</p><div class="literallayout"><p>CLK_NORMALIZED_COORDS_TRUE or<br />
CLK_NORMALIZED_COORDS_FALSE.</p></div><p>
</p>

<p>
The samplers used with an image in multiple calls to <code class="function">read_image{f|i|ui}</code> declared in a kernel must use the same value for <code class="constant">&lt;normalized coords&gt;</code>.
</p>
                        </td>
              </tr>
              <tr>
                <td align="left">
<p>
<code class="constant">&lt;address mode&gt;</code>
</p>
                        </td>
                <td align="left">
<p>
Specifies the image addressing-mode i.e. how out-of-range
image coordinates are handled. This must be a literal value
and can be one of the following predefined enums:
</p>

<p>
CLK_ADDRESS_MIRRORED_REPEAT - Flip the image
coordinate at every integer junction. This address
mode can only be used with normalized coordinates. If
normalized coordinates are not used, this addressing
mode may generate image coordinates that are
undefined.
</p>

<p>
CLK_ADDRESS_REPEAT - out-of-range image coordinates
are wrapped to the valid range. This <code class="constant">address mode</code> can
only be used with normalized coordinates. If normalized
coordinates are not used, this addressing mode may generate
image coordinates that are undefined.
</p>

<p>
CLK_ADDRESS_CLAMP_TO_EDGE - out-of-range image
coordinates are clamped to the extent.
</p>

<p>
CLK_ADDRESS_CLAMP - out-of-range image coordinates
will return a border color. 
</p>

<p>
CLK_ADDRESS_NONE - for this address mode the
programmer guarantees that the image coordinates used to
sample elements of the image refer to a location inside the
image; otherwise the results are undefined.
</p>
                        </td>
              </tr>
              <tr>
                <td align="left">
<p>
<code class="constant">&lt;filter mode&gt;</code>
</p>
                        </td>
                <td align="left">
<p>
Specifies the filtering mode to use. This must be a literal value
and can be one of the following predefined enums:
CLK_FILTER_NEAREST or CLK_FILTER_LINEAR.
</p>


<p>
Refer to section on Image Addressing and Filtering in the <a href="http://www.khronos.org/registry/cl/specs/opencl-1.1.pdf#page=252" target="OpenCL Spec">OpenCL specification</a> for a description of these filtering modes.
</p>
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
    </p>
        <p>
Samplers cannot be declared as arrays, pointers, or be used as the type for local variables inside a function or as the return value of a function defined in a program. Samplers cannot be passed as arguments to functions called by a <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a> function.
A sampler argument to a <a class="citerefentry" href="functionQualifiers.html"><span class="citerefentry"><span class="refentrytitle">__kernel</span></span></a>
function cannot be modified.
</p>
      </div>
      <div class="refsect1">
        <a id="notes"></a>
        <h2>Notes</h2>
        <p>
            The maximum number of samplers that can be declared in a kernel can be queried using the
            <code class="constant">CL_DEVICE_MAX_SAMPLERS</code> token in the table of OpenCL Device Queries for
            <a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>.
        </p>
        <p>
            If <code class="code">&lt;addressing mode&gt;</code> in sampler is CLK_ADDRESS_CLAMP, then out-of-range image
            coordinates return the border color. The border color selected depends on the image channel
            order and can be one of the following values:
        </p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem" style="list-style-type: disc">
                If the image channel order is CL_A, CL_INTENSITY, CL_Rx, CL_RA, CL_RGx,CL_RGBx, CL_ARGB, 
                CL_BGRA, or CL_RGBA, the border color is (0.0f, 0.0f,0.0f, 0.0f).
            </li>
            <li class="listitem" style="list-style-type: disc">
                If the image channel order is CL_R, CL_RG, CL_RGB, or CL_LUMINANCE, the border
                color is (0.0f, 0.0f, 0.0f, 1.0f)
            </li>
          </ul>
        </div>
        <p>
            A kernel that uses a sampler with the CL_ADDRESS_CLAMP addressing mode with multiple 
            images may result in additional samplers being used internally by an implementation. If
            the same sampler is used with multiple images called via 
            <a class="citerefentry" href="read_imagef2d.html"><span class="citerefentry"><span class="refentrytitle">read_imagef</span></span></a> or 
            <a class="citerefentry" href="read_imagei2d.html"><span class="citerefentry"><span class="refentrytitle">read_image{i|ui}</span></span></a> 
            then it is possible that an implementation may need to allocate an additional sampler to handle 
            the different border color values that may be needed depending on the image formats being used. 
            These implementation allocated samplers will count against the maximum sampler values supported 
            by the device and given by CL_DEVICE_MAX_SAMPLERS. Enqueuing a kernel that requires more samplers 
            than the implementation can support will result in a CL_OUT_OF_RESOURCES error being returned.
        </p>
      </div>
      <div class="refsect2">
        <a id="example1"></a>
        <h3>
            Example
        </h3>
        <div class="informaltable">
          <table border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
const sampler_t samplerA = CLK_NORMALIZED_COORDS_TRUE |
                           CLK_ADDRESS_REPEAT         |
                           CLK_FILTER_NEAREST;
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
        <p>
samplerA specifies a sampler that uses normalized coordinates, the repeat addressing mode and
a nearest filter.
</p>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />
                                                 
            <a href="http://www.khronos.org/registry/cl/specs/opencl-1.1.pdf#page=160" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="otherDataTypes.html"><span class="citerefentry"><span class="refentrytitle">Other Data Types</span></span></a>,
<a class="citerefentry" href="imageFunctions.html"><span class="citerefentry"><span class="refentrytitle">Image Read and Write Functions</span></span></a>,
            <a class="citerefentry" href="classDiagram.html"><span class="citerefentry"><span class="refentrytitle">Cardinality Diagram</span></span></a>

        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2010 The Khronos Group Inc.
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