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    <title>clEnqueueReadImage</title>
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    <div class="refentry">
      <a id="id-1"></a>
      <div class="titlepage"></div>
      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="clEnqueueReadImage"></a>
        <h1>
            clEnqueueReadImage
        </h1>
        <p>
            Enqueue commands to read from an image or image array object to host memory.
        </p>
      </div>
      <div class="refsynopsisdiv">
        <h2></h2>
        <div class="funcsynopsis">
          <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
            <tr valign="bottom">
              <td>
                <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
                    <a class="link" href="scalarDataTypes.html" target="pagedisplay">cl_int</a>
                    <strong class="fsfunc">clEnqueueReadImage</strong>
                (</code>
                <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_command_queue</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">command_queue</var>
                    , </td>
              </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_mem</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">image</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="enums.html#cl_bool" target="pagedisplay">cl_bool</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">blocking_read</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>const
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*origin</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>const
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*region</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">row_pitch</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">size_t</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">slice_pitch</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">void</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*ptr</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="scalarDataTypes.html" target="pagedisplay">cl_uint</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">num_events_in_wait_list</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>const
                        <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_event</a>
                         <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*event_wait_list</var>
                    , </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>
                    <a xmlns="http://www.w3.org/1999/xhtml" class="link" href="abstractDataTypes.html" target="pagedisplay">cl_event</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*event</var>
                    <code>)</code></td>
            </tr>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="parameters"></a>
        <h2>Parameters</h2>
        <div class="variablelist">
          <dl class="variablelist">
            <dt>
              <span class="term"> <code class="varname"> command_queue </code> </span>
            </dt>
            <dd>
              <p>
                        Refers to the command-queue in which the read command will be
                        queued. <code class="varname">command_queue</code> and <code class="varname">image</code>
                        must be created with the same OpenCL context.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> image </code> </span>
            </dt>
            <dd>
              <p>
                        Refers to a valid image or image array object.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> blocking_read </code> </span>
            </dt>
            <dd>
              <p>
                      Indicates if the read operations are <code class="varname">blocking</code> or
                      <code class="varname">non-blocking</code>.
                    </p>
              <p>
                      If <code class="varname">blocking_read</code> is <code class="constant">CL_TRUE</code>
                      i.e. the read command is blocking, <code class="function">clEnqueueReadImage</code>
                      does not return until the buffer data has been read and copied into memory
                      pointed to by <code class="varname">ptr</code>.
                    </p>
              <p>
                      If <code class="varname">blocking_read</code> is <code class="constant">CL_FALSE</code>
                      i.e. map operation is non-blocking, <code class="function">clEnqueueReadImage</code>
                      queues a non-blocking read command and returns. The contents of the
                      buffer that <code class="varname">ptr</code> points to cannot be used until the read
                      command has completed. The <code class="varname">event</code> argument returns an
                      event object which can be used to query the execution status of the read
                      command. When the read command has completed, the contents of the buffer
                      that <code class="varname">ptr</code> points to can be used by the application.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> origin </code> </span>
            </dt>
            <dd>
              <p>
                      Defines the (<span class="emphasis"><em>x, y, z</em></span>) offset in pixels in the 1D, 2D, or
                      3D image, the (<span class="emphasis"><em>x, y</em></span>) offset and the image index in the
                      image array or the (x) offset and the image index in the 1D image array.  If
                      <code class="varname">image</code> is a 2D image object, <code class="varname">origin</code>[2]
                      must be 0. If <code class="varname">image</code> is a 1D image or 1D image buffer
                      object, <code class="varname">origin</code>[1] and <code class="varname">origin</code>[2]
                      must be 0. If <code class="varname">image</code> is a 1D image array object,
                      <code class="varname">origin</code>[2] must be 0.  If <code class="varname">image</code>
                      is a 1D image array object, <code class="varname">origin</code>[1] describes the
                      image index in the 1D image array. If <code class="varname">image</code> is a 2D
                      image array object, <code class="varname">origin</code>[2] describes the image
                      index in the 2D image array.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> region </code> </span>
            </dt>
            <dd>
              <p>
                      Defines the (<span class="emphasis"><em>width, height, depth</em></span>) in pixels of the
                      1D, 2D or 3D rectangle, the (<span class="emphasis"><em>width, height</em></span>) in pixels
                      of the 2D rectangle and the number of images of a 2D image array or the
                      (<span class="emphasis"><em>width</em></span>) in pixels of the 1D rectangle and the number
                      of images of a 1D image array. If <code class="varname">image</code> is a 2D image
                      object, <code class="varname">region</code>[2] must be 1.  If <code class="varname">image</code>
                      is a 1D image or 1D image buffer object,  <code class="varname">region</code>[1]
                      and <code class="varname">region</code>[2] must be 1. If image is a 1D image array
                      object, <code class="varname">region</code>[2] must be 1.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> row_pitch </code> </span>
            </dt>
            <dd>
              <p>
                      The length of each row in bytes. This value must be greater than or
                      equal to the element size in bytes * <code class="varname">width</code>. If
                      <code class="varname">row_pitch</code> is set to 0, the appropriate row pitch
                      is calculated based on the size of each element in bytes multiplied by
                      <code class="varname">width</code>.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> slice_pitch </code> </span>
            </dt>
            <dd>
              <p>
                      Size in bytes of the 2D slice of the 3D region of a 3D image or
                      each image of a 1D or 2D image array being read.  This must be 0 if
                      <code class="varname">image</code> is a 1D or 2D image.  This value must be greater
                      than or equal to <code class="varname">row_pitch</code> * <code class="varname">height</code>.
                      If <code class="varname">slice_pitch</code> is set to 0, the appropriate slice
                      pitch is calculated based on the <code class="varname">row_pitch</code> *
                      <code class="varname">height</code>.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname"> ptr </code> </span>
            </dt>
            <dd>
              <p>
                      The pointer to a buffer in host memory where image data is to be written to.
                    </p>
            </dd>
            <dt>
              <span class="term"> <code class="varname">
                        event_wait_list
                    ,</code>
                    <code class="varname">
                        num_events_in_wait_list
                    </code>
                </span>
            </dt>
            <dd>
              <p>
                      Specify events that need to complete before this particular
                      command can be executed.  If <code class="varname">event_wait_list</code>
                      is NULL, then this particular command does not wait on any
                      event to complete. If <code class="varname">event_wait_list</code> is
                      NULL, <code class="varname">num_events_in_wait_list</code> must be 0. If
                      <code class="varname">event_wait_list</code> is not NULL, the list of events
                      pointed to by <code class="varname">event_wait_list</code> must be valid
                      and <code class="varname">num_events_in_wait_list</code> must be greater
                      than 0. The events specified in <code class="varname">event_wait_list</code>
                      act as synchronization points.  The context associated with events in
                      <code class="varname">event_wait_list</code> and <code class="varname">command_queue</code> must
                      be the same. The memory associated with <code class="varname">event_wait_list</code>
                      can be reused or freed after the function returns.
                    </p>
            </dd>
            <dt>
              <span class="term">
                    <code class="varname">
                        event
                    </code>
                </span>
            </dt>
            <dd>
              <p>
                      Returns an event object that identifies this particular read command
                      and can be used to query or queue a wait for this particular command
                      to complete. <code class="varname">event</code> can be NULL in which case
                      it will not be possible for the application to query the status of
                      this command or queue a wait for this command to complete.  If the
                      <code class="varname">event_wait_list</code> and the <code class="varname">event</code>
                      arguments are not NULL, the <code class="varname">event</code> argument should not
                      refer to an element of the <code class="varname">event_wait_list</code> array.
                    </p>
            </dd>
          </dl>
        </div>
      </div>
      <div class="refsect1">
        <a id="notes"></a>
        <h2>Notes</h2>
        <p>
          Calling <code class="function">clEnqueueReadImage</code> to read a region of the
          <code class="varname">image</code> with the <code class="varname">ptr</code> argument value set to
          <code class="varname">host_ptr</code> + (<code class="varname">origin</code>[2] * <code class="varname">image
          slice pitch</code> + <code class="varname">origin</code>[1] * <code class="varname">image
          row pitch</code> + <code class="varname">origin</code>[0] * <code class="varname">bytes per
          pixel</code>), where <code class="varname">host_ptr</code> is a pointer to the memory
          region specified when the <code class="varname">image</code> being read is created with
          <code class="constant">CL_MEM_USE_HOST_PTR</code>, must meet the following requirements in
          order to avoid undefined behavior:
        </p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem" style="list-style-type: disc">
              All commands that use this image object have finished execution before the read
              command begins execution.
            </li>
            <li class="listitem" style="list-style-type: disc">
              The <code class="varname">row_pitch</code> and <code class="varname">slice_pitch</code> argument
              values in <code class="function">clEnqueueReadImage</code> must be set to the image row
              pitch and slice pitch.
            </li>
            <li class="listitem" style="list-style-type: disc">
               The image object is not mapped.
            </li>
            <li class="listitem" style="list-style-type: disc">
              The image object is not used by any command-queue until the read command has
              finished execution.
            </li>
          </ul>
        </div>
      </div>
      <div class="refsect1">
        <a id="errors"></a>
        <h2>Errors</h2>
        <p>
          <code class="function">clEnqueueReadImage</code> returns <span class="errorname">CL_SUCCESS</span> if
          the function is executed successfully. Otherwise, it returns one of the following errors.
        </p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_COMMAND_QUEUE</span> if <code class="varname">command_queue</code>
              is not a valid command-queue.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_CONTEXT</span> if the context associated with
              <code class="varname">command_queue</code> and <code class="varname">image</code> are not the same
              or if the context associated with <code class="varname">command_queue</code> and events in
              <code class="varname">event_wait_list</code> are not the same.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_MEM_OBJECT</span> if <code class="varname">image</code> is not
              a valid image object.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_VALUE</span> if the region being read specified by
              <code class="varname">origin</code> and <code class="varname">region</code> is out of bounds or if
              <code class="varname">ptr</code> is a NULL value.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_VALUE</span> if values in <code class="varname">origin</code>
              and <code class="varname">region</code> do not follow rules described in the argument
              description for <code class="varname">origin</code> and <code class="varname">region</code>.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_EVENT_WAIT_LIST</span>
              if <code class="varname">event_wait_list</code> is NULL and
              <code class="varname">num_events_in_wait_list</code> &gt; 0,
              or <code class="varname">event_wait_list</code> is not NULL and
              <code class="varname">num_events_in_wait_list</code> is 0, or if event objects in
              <code class="varname">event_wait_list</code> are not valid events.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_IMAGE_SIZE</span> if image dimensions (image width,
              height, specified or compute row and/or slice pitch) for <code class="varname">image</code>
              are not supported by device associated with <code class="varname">queue</code>.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_IMAGE_FORMAT</span> if image format (image channel
              order and data type) for <code class="varname">image</code> are not supported by device
              associated with <code class="varname">queue</code>.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_MEM_OBJECT_ALLOCATION_FAILURE</span> if there is a failure to
              allocate memory for data store associated with <code class="varname">image</code>.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_OPERATION</span> if the device associated
              with <code class="varname">command_queue</code> does not support images
              (i.e. <code class="constant">CL_DEVICE_IMAGE_SUPPORT</code> specified in
              the table of allowed values for <code class="varname">param_name</code> for
              <a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>
              is <code class="constant">CL_FALSE</code>).
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_INVALID_OPERATION</span> if
              <code class="function">clEnqueueReadImage</code> is called on <code class="varname">image</code>
              which has been created with <code class="constant">CL_MEM_HOST_WRITE_ONLY</code> or
              <code class="constant">CL_MEM_HOST_NO_ACCESS</code></li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST</span> if the read
              and write operations are blocking and the execution status of any of the events
              in <code class="varname">event_wait_list</code> is a negative integer value.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_OUT_OF_RESOURCES</span> if there is a failure to allocate
              resources required by the OpenCL implementation on the device.
            </li>
            <li class="listitem" style="list-style-type: disc"><span class="errorname">CL_OUT_OF_HOST_MEMORY</span> if there is a failure to allocate
              resources required by the OpenCL implementation on the host.
            </li>
          </ul>
        </div>
      </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-1.2.pdf#page=98" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="clEnqueueWriteImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueWriteImage</span></span></a>,
            <a class="citerefentry" href="clEnqueueCopyImage.html"><span class="citerefentry"><span class="refentrytitle">clEnqueueCopyImage</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 © 2007-2011 The Khronos Group Inc.
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copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
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