am 0fe6febf: am b03ce7eb: Merge "docs: add fs to rs" into jb-mr1-dev

    <ol>

      <li><a href="#overview">Renderscript System Overview</a></li>

      <li><a href="#filterscript">Filterscript</a></li>

      <li>

        <a href="#creating-renderscript">Creating a Computation Renderscript</a>

        <ol>

          <li><a href="#creating-rs-file">Creating the Renderscript file</a></li>

          <li><a href="#calling">Calling the Renderscript code</a></li>

        </ol>

      </li>

<p>For a more detailed explanation of how all of these layers work together, see

  <a href="{@docRoot}guide/topics/renderscript/advanced.html">Advanced Renderscript</a>.<p>

<h2 id="filterscript">Filterscript</h2>

<p>Introduced in Android 4.2 (API Level 17), Filterscript defines a subset of Renderscript

that focuses on image processing operations, such as those

that you would typically write with an OpenGL ES fragment shader. You still write your scripts

using the standard Renderscript runtime APIs, but within stricter

constraints that ensure wider compatibility and improved optimization across

CPUs, GPUs, and DSPs. At compile time, the precompiler evaluates Filterscript files and

applies a more stringent set of warnings and errors than

it does for standard Renderscript files. The following list describes the major constraints

of Filterscript when compared to Renderscript:</p>

<ul>

<li>Inputs and return values of root functions cannot contain pointers. The default root function

signature contains pointers, so you must use the <code>__attribute__((kernel))</code> attribute to declare a custom

root function when using Filterscript.</li>

<li>Built-in types cannot exceed 32-bits.</li>

<li>Filterscript must always use relaxed floating point precision by using the

<code>rs_fp_relaxed</code> pragma.</li>

<li>Filterscript files must end with an <code>.fs</code> extension, instead of an <code>.rs</code> extension.</li>

</ul>

<h2 id="creating-renderscript">Creating a Renderscript</h2>

<p>Renderscripts scale to the amount of

<p>Renderscript scales to the amount of

processing cores available on the device. This is enabled through a function named

<code>rsForEach()</code> (or the <code>forEach_root()</code> method at the Android framework level).

that automatically partitions work across available processing cores on the device. 

For now, Renderscript can only take advantage of CPU

cores, but in the future, they can potentially run on other types of processors such as GPUs and

DSPs.</p>

that automatically partitions work across available processing cores on the device.</p>

<p>Implementing a Renderscript involves creating a <code>.rs</code> file that contains

your Renderscript code and calling it at the Android framework level with the

  <li>A pragma declaration (<code>#pragma version(1)</code>) that declares the version of

  Renderscript that you are using (1 is the only value for now).</li>

  <li><p>A <code>root()</code> function that is the main worker function. The root function is

  called by the <code>rsForEach</code> function, which allows the Renderscript code to be called and

  executed on multiple cores if they are available. The <code>root()</code> function must return

  <li><p>A root function (or kernel) that is the main entry point to your Renderscript.

  The default <code>root()</code> function must return

  <code>void</code> and accept the following arguments:</p>

    <ul>

      <li>The size of the user-defined data.</li>

    </ul>

  <p>Starting in Android 4.1 (API Level 16), you can choose to define your own root function arguments

  without adhering to the default root function signature described previously. In addition,

  you can declare multiple root functions in the same Renderscript. To do this, use the <code>__attribute__((kernel))</code>

  attribute to define a custom root function. For example, here's a root function

  that returns a <code>uchar4</code> and accepts two <code>uint32_t</code> types: </p>

  <pre>

  uchar4 __attribute__((kernel)) root(uint32_t x, uint32_t y) {

    ...

  }

  </pre>

  </li>

  <li>An optional <code>init()</code> function. This allows you to do any initialization 

  before the <code>root()</code> function runs, such as initializing variables. This

  before the root function runs, such as initializing variables. This

  function runs once and is called automatically when the Renderscript starts, before anything

  else in your Renderscript.</li>

}

</pre>

<h4>Setting floating point precision</h4>

<p>You can define the floating point precision required by your compute algorithms. This is useful if you

 require less precision than the IEEE 754-2008 standard (used by default). You can define

the floating-point precision level of your script with the following pragmas:</p>

<ul>

  <li><code>#pragma rs_fp_full</code> (default if nothing is specified): For apps that

    require floating point precision as outlined by the IEEE 754-2008 standard.

</li>

  <li><code>#pragma rs_fp_relaxed</code> - For apps that don’t require

    strict IEEE 754-2008 compliance and can tolerate less precision. This mode enables

    flush-to-zero for denorms and round-towards-zero.

</li>

  <li><code>#pragma rs_fp_imprecise</code> - For apps that don’t have stringent precision requirements. This mode enables

    everything in <code>rs_fp_relaxed</code> along with the following:

<ul>

  <li>Operations resulting in -0.0 can return +0.0 instead.</li>

  <li>Operations on INF and NAN are undefined.</li>

</ul>

</li>

</ul>

<h4>Script intrinsics</h4>

<p>Renderscript adds support for a set of script intrinsics, which are pre-implemented

filtering primitives that reduce the amount of

code that you need to write. They also are implemented to ensure that your app gets the

maximum performance gain possible.</p>

<p>

Intrinsics are available for the following:

<ul>

  <li>{@link android.renderscript.ScriptIntrinsicBlend Blends}</li>

  <li>{@link android.renderscript.ScriptIntrinsicBlur Blur}</li>

  <li>{@link android.renderscript.ScriptIntrinsicColorMatrix Color matrix}</li>

  <li>{@link android.renderscript.ScriptIntrinsicConvolve3x3 3x3 convolve}</li>

  <li>{@link android.renderscript.ScriptIntrinsicConvolve5x5 5x5 convolve}</li>

  <li>{@link android.renderscript.ScriptIntrinsicLUT Per-channel lookup table}</li>

  <li>{@link android.renderscript.ScriptIntrinsicYuvToRGB Converting an Android YUV buffer to RGB}</li>

</ul>

<h3 id="calling">Calling the Renderscript code</h3>

<p>You can call the Renderscript from your Android framework code by

is optional, but useful if your Renderscript requires additional information other than

the necessary memory allocations.</p>

<h3>Setting floating point precision</h3>

<p>You can define the floating point precision required by your compute algorithms. This is useful if you

 require less precision than the IEEE 754-2008 standard (used by default). You can define

the floating-point precision level of your script with the following pragmas:</p>

<ul>

  <li><code>#pragma rs_fp_full</code> (default if nothing is specified): For apps that

    require floating point precision as outlined by the IEEE 754-2008 standard.

</li>

  <li><code>#pragma rs_fp_relaxed</code> - For apps that don’t require

    strict IEEE 754-2008 compliance and can tolerate less precision. This mode enables

    flush-to-zero for denorms and round-towards-zero.

</li>

  <li><code>#pragma rs_fp_imprecise</code> - For apps that don’t have stringent precision requirements. This mode enables

    everything in <code>rs_fp_relaxed</code> along with the following:

<ul>

  <li>Operations resulting in -0.0 can return +0.0 instead.</li>

  <li>Operations on INF and NAN are undefined.</li>

</ul>

</li>

</ul>

 No newline at end of file

<h4>Script groups</h4>

<p>You can group Renderscript scripts together and execute them all with a single call as though

they were part of a single script. This allows Renderscript to optimize execution of the scripts

in ways that it could not do if the scripts were executed individually.</p>

<p>To build a script groupm, use the {@link android.renderscript.ScriptGroup.Builder} class to create a {@link android.renderscript.ScriptGroup}

defining the operations. At execution time, Renderscript optimizes the run order and the connections between these

operations for best performance.

<p class="note"><strong>Important:</strong> The script group must be a direct acyclic graph for this feature to work.</p>