docs/html/guide/topics/graphics/hardware-accel.jd

page.title=Hardware Acceleration
parent.title=Graphics
parent.link=index.html
@jd:body


  <div id="qv-wrapper">
    <div id="qv">
      <h2>In this document</h2>

      <ol>
        <li><a href="#controlling">Controlling Hardware Acceleration</a></li>
        <li><a href="#determining">Determining if a View is Hardware Accelerated</a></li>
        <li><a href="#model">Android Drawing Models</a>

          <ol>
            <li><a href="#software-model">Software-based drawing model</a></li>
            <li><a href="#hardware-model">Hardware accelerated drawing model</a></li>
          </ol>
        </li>

        <li>
          <a href="#unsupported">Unsupported Drawing Operations</a>
        </li>



        <li>
          <a href="#layers">View Layers</a>

          <ol>
            <li><a href="#layers-anims">View Layers and Animations</a></li>
          </ol>
        </li>

        <li><a href="#tips">Tips and Tricks</a></li>
      </ol>

      <h2>See also</h2>

      <ol>
        <li><a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL with the Framework
        APIs</a></li>

        <li><a href="{@docRoot}guide/topics/renderscript/index.html">Renderscript</a></li>
      </ol>
    </div>
  </div>

  <p>Beginning in Android 3.0 (API level 11), the Android 2D rendering pipeline supports hardware
  acceleration, meaning that all drawing operations that are performed on a {@link
  android.view.View}'s canvas use the GPU. Because of the increased resources required to enable
  hardware acceleration, your app will consume more RAM.</p>

  <p>Hardware acceleration is enabled by default if your Target API level is &gt;=14, but can also
  be explicitly enabled. If your application uses only standard views and {@link
  android.graphics.drawable.Drawable}s, turning it on globally should not cause any adverse drawing
  effects. However, because hardware acceleration is not supported for all of the 2D drawing
  operations, turning it on might affect some of your custom views or drawing calls. Problems
  usually manifest themselves as invisible elements, exceptions, or wrongly rendered pixels. To
  remedy this, Android gives you the option to enable or disable hardware acceleration at multiple
  levels. See <a href="#controlling">Controlling Hardware Acceleration</a>.</p>

  <p>If your application performs custom drawing, test your application on actual hardware devices
  with hardware acceleration turned on to find any problems. The <a
  href="#drawing-support">Unsupported drawing operations</a> section describes known issues with
  hardware acceleration and how to work around them.</p>

 <h2 id="controlling">Controlling Hardware Acceleration</h2>
  <p>You can control hardware acceleration at the following levels:</p>
  <ul>
    <li>Application</li>

    <li>Activity</li>

    <li>Window</li>

    <li>View</li>
  </ul>

  <h4>Application level</h4>
  <p>In your Android manifest file, add the following attribute to the
  <a href="{@docRoot}guide/topics/manifest/application-element.html">
    <code>&lt;application&gt;</code></a> tag to enable hardware acceleration for your entire
  application:</p>

<pre>
&lt;application android:hardwareAccelerated="true" ...&gt;
</pre>

  <h4>Activity level</h4>
  <p>If your application does not behave properly with hardware acceleration turned on globally, you
  can control it for individual activities as well. To enable or disable hardware acceleration at
  the activity level, you can use the <code>android:hardwareAccelerated</code> attribute for
  the <a href="{@docRoot}guide/topics/manifest/activity-element.html">
  <code>&lt;activity&gt;</code></a> element. The following example enables hardware acceleration for
  the entire application but disables it for one activity:</p>

<pre>
&lt;application android:hardwareAccelerated="true"&gt;
    &lt;activity ... /&gt;
    &lt;activity android:hardwareAccelerated="false" /&gt;
&lt;/application&gt;
</pre>

  <h4>Window level</h4>
  <p>If you need even more fine-grained control, you can enable hardware acceleration for a given
  window with the following code:</p>

<pre>
getWindow().setFlags(
    WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED,
    WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED);

</pre>

<p class="note"><strong>Note</strong>:  You currently cannot disable hardware acceleration at
the window level.</p>

  <h4>View level</h4>

  <p>You can disable hardware acceleration for an individual view at runtime with the
following code:</p>

<pre>
myView.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
</pre>

<p class="note"><strong>Note</strong>: You currently cannot enable hardware acceleration at
the view level. View layers have other functions besides disabling hardware acceleration. See <a
href="#layers">View layers</a> for more information about their uses.</p>

  <h2 id="determining">Determining if a View is Hardware Accelerated</h2>

  <p>It is sometimes useful for an application to know whether it is currently hardware
  accelerated, especially for things such as custom views. This is particularly useful if your
  application does a lot of custom drawing and not all operations are properly supported by the new
  rendering pipeline.</p>

  <p>There are two different ways to check whether the application is hardware accelerated:</p>

  <ul>
    <li>{@link android.view.View#isHardwareAccelerated View.isHardwareAccelerated()} returns
    <code>true</code> if the {@link android.view.View} is attached to a hardware accelerated
    window.</li>

    <li>{@link android.graphics.Canvas#isHardwareAccelerated Canvas.isHardwareAccelerated()}
    returns <code>true</code> if the {@link android.graphics.Canvas} is hardware accelerated</li>
  </ul>

  <p>If you must do this check in your drawing code, use {@link
  android.graphics.Canvas#isHardwareAccelerated Canvas.isHardwareAccelerated()} instead of {@link
  android.view.View#isHardwareAccelerated View.isHardwareAccelerated()} when possible. When a view
  is attached to a hardware accelerated window, it can still be drawn using a non-hardware
  accelerated Canvas. This happens, for instance, when drawing a view into a bitmap for caching
  purposes.</p>


  <h2 id="model">Android Drawing Models</h2>

  <p>When hardware acceleration is enabled, the Android framework utilizes a new drawing model that
  utilizes <em>display lists</em> to render your application to the screen. To fully understand
  display lists and how they might affect your application, it is useful to understand how Android
  draws views without hardware acceleration as well. The following sections describe the
  software-based  and hardware-accelerated drawing models.</p>

<h3>Software-based drawing model</h3>
<p>In the software drawing model, views are drawn with the following two steps:</p>
  <ol>
    <li>Invalidate the hierarchy</li>

    <li>Draw the hierarchy</li>
  </ol>

  <p>Whenever an application needs to update a part of its UI, it invokes {@link
  android.view.View#invalidate invalidate()} (or one of its variants) on any view that has changed
  content. The invalidation messages are propagated all the way up the view hierarchy to compute
  the regions of the screen that need to be redrawn (the dirty region). The Android system then
  draws any view in the hierarchy that intersects with the dirty region. Unfortunately, there are
  two drawbacks to this drawing model:</p>
  <ul>
    <li>First, this model requires execution of a lot of code on every draw pass. For example, if
your application calls {@link android.view.View#invalidate invalidate()} on a button and that
button sits on top of another view, the Android system redraws the view even though it hasn't
changed.</li>
    <li>The second issue is that the drawing model can hide bugs in your application. Since the
  Android system redraws views when they intersect the dirty region, a view whose content you
  changed might be redrawn even though {@link android.view.View#invalidate invalidate()} was not
  called on it. When this happens, you are relying on another view being invalidated to obtain the
  proper behavior. This behavior can change every time you modify your application. Because of
  this, you should always call {@link android.view.View#invalidate invalidate()} on your custom
  views whenever you modify data or state that affects the view’s drawing code.</li>
</ul>

  <p class="note"><strong>Note</strong>: Android views automatically call {@link
  android.view.View#invalidate invalidate()} when their properties change, such as the background
  color or the text in a {@link android.widget.TextView}.</p>

  <h3>Hardware accelerated drawing model</h3>
  <p>The Android system still uses {@link android.view.View#invalidate invalidate()} and {@link
  android.view.View#draw draw()} to request screen updates and to render views, but handles the
  actual drawing differently. Instead of executing the drawing commands immediately, the Android
  system records them inside display lists, which contain the output of the view hierarchy’s
  drawing code. Another optimization is that the Android system only needs to record and update
  display lists for views marked dirty by an {@link android.view.View#invalidate invalidate()}
  call. Views that have not been invalidated can be redrawn simply by re-issuing the previously
  recorded display list. The new drawing model contains three stages:</p>

  <ol>
    <li>Invalidate the hierarchy</li>

    <li>Record and update display lists</li>

    <li>Draw the display lists</li>
  </ol>

  <p>With this model, you cannot rely on a view intersecting the dirty region to have its {@link
  android.view.View#draw draw()} method executed. To ensure that the Android system records a
  view’s display list, you must call {@link android.view.View#invalidate invalidate()}. Forgetting
  to do so causes a view to look the same even after it has been changed.</p>

  <p>Using display lists also benefits animation performance because setting specific properties,
  such as alpha or rotation, does not require invalidating the targeted view (it is done
  automatically). This optimization also applies to views with display lists (any view when your
  application is hardware accelerated.) For example, assume there is a {@link
  android.widget.LinearLayout} that contains a {@link android.widget.ListView} above a {@link
  android.widget.Button}. The display list for the {@link android.widget.LinearLayout} looks like
  this:</p>

  <ul>
    <li>DrawDisplayList(ListView)</li>

    <li>DrawDisplayList(Button)</li>
  </ul>

  <p>Assume now that you want to change the {@link android.widget.ListView}'s opacity. After
  invoking <code>setAlpha(0.5f)</code> on the {@link android.widget.ListView}, the display list now
  contains this:</p>

  <ul>
    <li>SaveLayerAlpha(0.5)</li>

    <li>DrawDisplayList(ListView)</li>

    <li>Restore</li>

    <li>DrawDisplayList(Button)</li>
  </ul>

  <p>The complex drawing code of {@link android.widget.ListView} was not executed. Instead, the
  system only updated the display list of the much simpler {@link android.widget.LinearLayout}. In
  an application without hardware acceleration enabled, the drawing code of both the list and its
  parent are executed again.</p>

  <h2 id="unsupported">Unsupported Drawing Operations</h2>

  <p>When hardware accelerated, the 2D rendering pipeline supports the most commonly used {@link
  android.graphics.Canvas} drawing operations as well as many less-used operations. All of the
  drawing operations that are used to render applications that ship with Android, default widgets
  and layouts, and common advanced visual effects such as reflections and tiled textures are
  supported.</p>

  <p>The following table describes the support level of various operations across API levels:</p>

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        <td class="g_neg">&#10007;</td>
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  <h3 id="scaling">Canvas Scaling</h3>

  <p>The hardware accelerated 2D rendering pipeline was built first to support unscaled drawing,
  with some drawing operations degrading quality significantly at higher scale values. These
  operations are implemented as textures drawn at scale 1.0, transformed by the GPU.  In API level
  &lt;17, using these operations will result in scaling artifacts increasing with scale.</p>

  The following table shows when implementation was changed to correctly handle large scales:

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    </tr>
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    <tr>
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        <td class="g_neg">&#10007;</td>
        <td class="w_neg">&#10007;</td>
        <td class="g_neg">&#10007;</td>
    </tr>
    <tr>
        <td class="s10">Shadow layer</td>
        <td class="g_neg">&#10007;</td>
        <td class="w_neg">&#10007;</td>
        <td class="g_neg">&#10007;</td>
    </tr>
    </tbody>
  </table>

  <p class="note"><strong>Note</strong>: 'Simple' shapes are <code>drawRect()</code>,
  <code>drawCircle()</code>, <code>drawOval()</code>, <code>drawRoundRect()</code>, and
  <code>drawArc()</code> (with useCenter=false) commands issued with a Paint that doesn't have a
  PathEffect, and doesn't contain non-default joins (via <code>setStrokeJoin()</code> /
  <code>setStrokeMiter()</code>). Other instances of those draw commands fall under 'Complex,' in
  the above chart.</p>

  <p>If your application is affected by any of these missing features or limitations, you can turn
  off hardware acceleration for just the affected portion of your application by calling {@link
  android.view.View#setLayerType setLayerType(View.LAYER_TYPE_SOFTWARE, null)}. This way, you can
  still take advantage of hardware acceleration everywhere else. See <a
  href="#controlling">Controlling Hardware Acceleration</a> for more information on how to enable
  and disable hardware acceleration at different levels in your application.

  <h2 id="layers">View Layers</h2>

  <p>In all versions of Android, views have had the ability to render into off-screen buffers,
either by using a view's drawing cache, or by using {@link android.graphics.Canvas#saveLayer
  Canvas.saveLayer()}. Off-screen buffers, or layers, have several uses. You can use them to get
  better performance when animating complex views or to apply composition effects. For instance,
  you can implement fade effects using <code>Canvas.saveLayer()</code> to temporarily render a view
  into a layer and then composite it back on screen with an opacity factor.</p>

  <p>Beginning in Android 3.0 (API level 11), you have more control on how and when to use layers
  with the {@link android.view.View#setLayerType View.setLayerType()} method. This API takes two
  parameters: the type of layer you want to use and an optional {@link android.graphics.Paint}
  object that describes how the layer should be composited. You can use the {@link
  android.graphics.Paint} parameter to apply color filters, special blending modes, or opacity to a
  layer. A view can use one of three layer types:</p>

  <ul>
    <li>{@link android.view.View#LAYER_TYPE_NONE}: The view is rendered normally and is not backed
    by an off-screen buffer. This is the default behavior.</li>

    <li>{@link android.view.View#LAYER_TYPE_HARDWARE}: The view is rendered in hardware into a
    hardware texture if the application is hardware accelerated. If the application is not hardware
    accelerated, this layer type behaves the same as {@link
    android.view.View#LAYER_TYPE_SOFTWARE}.</li>

    <li>{@link android.view.View#LAYER_TYPE_SOFTWARE}: The view is rendered in software into a
    bitmap.</li>
  </ul>

  <p>The type of layer you use depends on your goal:</p>

  <ul>
    <li><strong>Performance</strong>: Use a hardware layer type to render a view into a hardware
    texture. Once a view is rendered into a layer, its drawing code does not have to be executed
    until the view calls {@link android.view.View#invalidate invalidate()}. Some animations, such as
    alpha animations, can then be applied directly onto the layer, which is very efficient
    for the GPU to do.</li>

    <li><strong>Visual effects</strong>: Use a hardware or software layer type and a {@link
    android.graphics.Paint} to apply special visual treatments to a view. For instance, you can
    draw a view in black and white using a {@link
    android.graphics.ColorMatrixColorFilter}.</li>

    <li><strong>Compatibility</strong>: Use a software layer type to force a view to be rendered in
    software. If a view that is hardware accelerated (for instance, if your whole
    application is hardware acclerated), is having rendering problems, this is an easy way to work
around limitations of the hardware rendering
    pipeline.</li>
  </ul>

  <h3 id="layers-anims">View layers and animations</h3>

  <p>Hardware layers can deliver faster and smoother animations when your application
is hardware accelerated. Running an animation at 60 frames per second is not always possible when
animating complex views that issue a lot of drawing operations. This can be alleviated by
using hardware layers to render the view to a hardware texture. The hardware texture can
then be used to animate the view, eliminating the need for the view to constantly redraw itself
when it is being animated. The view is not redrawn unless you change the view's
properties, which calls {@link android.view.View#invalidate invalidate()}, or if you call {@link
android.view.View#invalidate invalidate()} manually. If you are running an animation in
your application and do not obtain the smooth results you want, consider enabling hardware layers on
your animated views.</p>

  <p>When a view is backed by a hardware layer, some of its properties are handled by the way the
  layer is composited on screen. Setting these properties will be efficient because they do not
  require the view to be invalidated and redrawn. The following list of properties affect the way
  the layer is composited. Calling the setter for any of these properties results in optimal
  invalidation and no redrawing of the targeted view:</p>

  <ul>
    <li><code>alpha</code>: Changes the layer's opacity</li>

    <li><code>x</code>, <code>y</code>, <code>translationX</code>, <code>translationY</code>:
Changes the layer's position</li>

    <li><code>scaleX</code>, <code>scaleY</code>: Changes the layer's size</li>

    <li><code>rotation</code>, <code>rotationX</code>, <code>rotationY</code>: Changes the
    layer's orientation in 3D space</li>

    <li><code>pivotX</code>, <code>pivotY</code>: Changes the layer's transformations origin</li>
  </ul>

  <p>These properties are the names used when animating a view with an {@link
  android.animation.ObjectAnimator}. If you want to access these properties, call the appropriate
  setter or getter. For instance, to modify the alpha property, call {@link
  android.view.View#setAlpha setAlpha()}. The following code snippet shows the most efficient way
  to rotate a viewiew in 3D around the Y-axis:</p>
  <pre>
view.setLayerType(View.LAYER_TYPE_HARDWARE, null);
ObjectAnimator.ofFloat(view, "rotationY", 180).start();
</pre>

  <p>Because hardware layers consume video memory, it is highly recommended that you enable them
only for the duration of the animation and then disable them after the animation is done. You
can accomplish this using animation listeners:</p>
  <pre>
View.setLayerType(View.LAYER_TYPE_HARDWARE, null);
ObjectAnimator animator = ObjectAnimator.ofFloat(view, "rotationY", 180);
animator.addListener(new AnimatorListenerAdapter() {
    &#064;Override
    public void onAnimationEnd(Animator animation) {
        view.setLayerType(View.LAYER_TYPE_NONE, null);
    }
});
animator.start();
</pre>

  <p>For more information on property animation, see <a href=
  "{@docRoot}guide/topics/graphics/prop-animation.html">Property Animation</a>.</p>

 <h2 id="tips">Tips and Tricks</h2>

  <p>Switching to hardware accelerated 2D graphics can instantly increase performance, but you
  should still design your application to use the GPU effectively by following these
  recommendations:</p>

  <dl>
    <dt><strong>Reduce the number of views in your application</strong></dt>

    <dd>The more views the system has to draw, the slower it will be. This applies to the software
    rendering pipeline as well. Reducing views is one of the easiest ways to optimize your UI.</dd>

    <dt><strong>Avoid overdraw</strong></dt>

    <dd>Do not draw too many layers on top of each other. Remove any views that are completely
    obscured by other opaque views on top of it. If you need to draw several layers blended on top
    of each other, consider merging them into a single layer. A good rule of thumb with current
    hardware is to not draw more than 2.5 times the number of pixels on screen per frame
    (transparent pixels in a bitmap count!).</dd>

    <dt><strong>Don't create render objects in draw methods</strong></dt>

    <dd>A common mistake is to create a new {@link android.graphics.Paint} or a new {@link
android.graphics.Path} every time a rendering method is invoked. This forces the garbage
collector to run more often and also bypasses caches and optimizations in the hardware
pipeline.</dd>

    <dt><strong>Don't modify shapes too often</strong></dt>

    <dd>Complex shapes, paths, and circles for instance, are rendered using texture masks. Every
    time you create or modify a path, the hardware pipeline creates a new mask, which can be
    expensive.</dd>

    <dt><strong>Don't modify bitmaps too often</strong></dt>

    <dd>Every time you change the content of a bitmap, it is uploaded again as a GPU texture the
    next time you draw it.</dd>

    <dt><strong>Use alpha with care</strong></dt>

    <dd>When you make a view translucent using {@link android.view.View#setAlpha setAlpha()},
    {@link android.view.animation.AlphaAnimation}, or {@link android.animation.ObjectAnimator}, it
    is rendered in an off-screen buffer which doubles the required fill-rate. When applying alpha
    on very large views, consider setting the view's layer type to
    <code>LAYER_TYPE_HARDWARE</code>.</dd>
  </dl>