1page.title=Optimizing Performance and Battery Life 2 3@jd:body 4 5<div id="tb-wrapper"> 6<div id="tb"> 7<h2>This lesson teaches you to</h2> 8<ol> 9 <li><a href="#Basic">Basic Optimization</a></li> 10 <li><a href="#Animations">Best Practices for Animations</a></li> 11 <li><a href="#ReduceSize">Reduce the Size of Your Bitmap Assets</a></li> 12 <li><a href="#CombineBitmaps">Combine Bitmap Assets</a></li> 13 <li><a href="#AntiAlias">Disable Anti-Aliasing when Drawing Scaled Bitmaps</a></li> 14 <li><a href="#OutDrawing">Move Expensive Operations Outside the Drawing Method</a></li> 15</ol> 16<h2>You should also read</h2> 17<ul> 18 <li><a href="{@docRoot}design/wear/watchfaces.html">Watch Faces for Android Wear</a></li> 19 <li><a href="http://android-developers.blogspot.com/2014/12/making-performant-watch-face.html"> 20Making a performant watch face</a></li> 21 <li><a href="http://android-developers.blogspot.com/2016/04/deprecation-of-bindlistener.html"> 22Deprecation of BIND_LISTENER with Android Wear APIs</a></li> 23</ul> 24</div> 25</div> 26 27<p>This lesson has tips for conserving power and improving performance. 28A watch face runs continuously, so it must use power 29efficiently. </p> 30 31<p>Services must not perform unnecessary computations. 32Watch faces with animations must run smoothly while accommodating 33notification cards and system indicators.</p> 34 35<h2 id="Basic">Basic Optimization</h2> 36 37<p>This section contains best practices for improving efficiency during 38periods when a watch face is inactive.</p> 39 40<h3>Use callbacks in WatchFaceService.Engine</h3> 41 42<p>Ensure that your watch face performs 43computations only when active; use callbacks 44in <a href="{@docRoot}reference/android/support/wearable/watchface/ 45WatchFaceService.Engine.html">{@code WatchFaceService.Engine}</a>. 46Preferably, use the following methods of that class to determine if 47the watch face is visible:</p> 48 49<ul> 50 <li>{@code onVisibilityChanged(boolean)}</li> 51 <li>{@code isVisible()}</li> 52</ul> 53 54<p>Alternatively, use the following methods of the same class 55(<a href="{@docRoot}reference/android/support/wearable/watchface/ 56WatchFaceService.Engine.html">{@code WatchFaceService.Engine}</a>):</p> 57 58<ul> 59 <li>{@code onCreate()}</li> 60 <li>{@code onDestroy()}</li> 61</ul> 62 63<h3>Use listeners registered with the DataApi interface</h3> 64 65<p>To listen for events, use live listeners that are registered 66with <a href="https://developers.google.com/android/reference/com/google/ 67android/gms/wearable/DataApi.html#addListener 68(com.google.android.gms.common.api.GoogleApiClient, com. 69google.android.gms.wearable.DataApi.DataListener)">{@code DataApi.addListener}</a>. 70For an example, see <a href="{@docRoot}training/wearables/data-layer/ 71data-items.html#ListenEvents">Syncing Data Items</a>.</p> 72 73<p>Do not use <a href="https://developers.google.com/ 74android/reference/com/google/android/gms/wearable/ 75WearableListenerService">{@code WearableListenerService}</a> to listen for 76events, because it is 77called whether or not a watch face is active. For more information, see 78<a href="http://android-developers.blogspot.com/2016/04/ 79deprecation-of-bindlistener.html">Deprecation of BIND_LISTENER 80with Android Wear APIs</a>.</p> 81 82<p>Do not register a broadcast receiver in the Android manifest file 83to get system events such as time zone changes, battery events, etc., because 84the <a href="{@docRoot}reference/android/content/BroadcastReceiver.html">{@code BroadcastReceiver}</a> 85is called whether or not a watch face is active. However, you can use the 86<a href="{@docRoot}reference/android/content/Context.html#registerReceiver(android. 87content.BroadcastReceiver, android.content.IntentFilter)">{@code registerReceiver}</a> method 88of the {@code Context} class to register a receiver.</p> 89 90<h3>Monitor power consumption</h3> 91 92<p>The <a href="https://play.google.com/store/apps/details?id=com.google.android.wearable.app&hl=en"> 93Android Wear companion app</a> enables developers and users to see how much battery 94is consumed by different processes 95on the wearable device (under <strong>Settings</strong> > <strong>Watch 96battery</strong>).</p> 97 98<p>For information about features introduced in Android 5.0 that help you improve battery life, 99see <a href="{@docRoot}about/versions/android-5.0.html#Power">Project Volta</a>.</p> 100 101<h2 id="Animations">Best Practices for Animations</h2> 102 103<p>The best practices in this section help to reduce the power consumption of animations.</p> 104 105<h3>Reduce the frame rate of animations</h3> 106 107<p>Animations are often computationally expensive and consume a significant amount of power. Most 108animations look fluid at 30 frames per second, so you should avoid running your animations 109at a higher frame rate.</p> 110 111<h3>Let the CPU sleep between animations</h3> 112 113<p>Animations and small changes to the contents of the watch face wake up the CPU. Your watch 114face should let the CPU sleep in between animations. For example, you can use short bursts of 115animation every second in interactive mode and then let the CPU sleep until the next second. 116Letting the CPU sleep often, even briefly, can significantly reduce power consumption.</p> 117 118<p>To maximize battery life, use animations sparingly. Even a blinking colon wakes up the CPU with 119every blink and hurts battery life.</p> 120 121<h2 id="ReduceSize">Reduce the Size of Your Bitmap Assets</h2> 122 123<p>Many watch faces consist of a background image and other graphic assets that are transformed 124and overlapped on top of the background image, such as clock hands and other elements of the design 125that move over time. Typically these graphic elements are rotated (and sometimes scaled) inside the 126<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 127method every time the system redraws the watch face, as described in 128<a href="{@docRoot}training/wearables/watch-faces/drawing.html#Drawing">Draw Your Watch 129Face</a>.</p> 130 131<p>The larger these graphic assets are, the more computationally expensive it is to transform them. 132Transforming large graphic assets in the 133<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 134method drastically reduces the frame rate at which the system can run your animations.</p> 135 136<div id="fig1" style="float:right;width:250px;margin-left:25px"> 137<img src="{@docRoot}training/wearables/watch-faces/images/ClockHandFull.png" alt="" 138 width="180" height="180"/> 139<img src="{@docRoot}training/wearables/watch-faces/images/ClockHandCropped.png" alt="" 140 width="15" height="65" style="margin-left:25px"/> 141<p class="img-caption"> 142<strong>Figure 1.</strong> Clock hands can be cropped to remove extra pixels.</p> 143</div> 144 145<p>To improve the performance of your watch face:</p> 146 147<ul> 148<li>Do not use graphic elements that are larger than you need.</li> 149<li>Remove extra transparent pixels around the edges.</li> 150</ul> 151 152<p>The example clock hand on the left side of <a href="#fig1">Figure 1</a> can be reduced in size 153by 97%.</p> 154 155<p>Reducing the size of your bitmap assets as described in this section not only improves 156the performance of your animations, but it also saves power.</p> 157 158<h2 id="CombineBitmaps">Combine Bitmap Assets</h2> 159 160<p>If you have bitmaps that are often drawn together, consider combining them into the same 161graphic asset. You can often combine the background image in interactive mode with the tick 162marks to avoid drawing two full-screen bitmaps every time the system redraws the watch face.</p> 163 164<h2 id="AntiAlias">Disable Anti-Aliasing when Drawing Scaled Bitmaps</h2> 165 166<p>When you draw a scaled bitmap on the {@link android.graphics.Canvas} object using the {@link 167android.graphics.Canvas#drawBitmap(android.graphics.Bitmap, float, float, android.graphics.Paint) 168Canvas.drawBitmap()} method, you can provide a {@link android.graphics.Paint} instance to configure 169several options. To improve performance, disable anti-aliasing using the {@link 170android.graphics.Paint#setAntiAlias setAntiAlias()} method, since this option does not have any 171effect on bitmaps.</p> 172 173<div id="fig2" style="float:right;width:250px;margin-left:40px;margin-top:12px"> 174<img src="{@docRoot}training/wearables/watch-faces/images/BitmapFilterDisabled.png" alt="" 175 width="70" height="70" style="margin-left:20px"/> 176<img src="{@docRoot}training/wearables/watch-faces/images/BitmapFilterEnabled.png" alt="" 177 width="70" height="70" style="margin-left:20px"/> 178<p class="img-caption"><strong>Figure 2.</strong> Example of bitmap filtering disabled (left) and 179enabled (right).</p> 180</div> 181 182<h3 id="BitmapFiltering">Use bitmap filtering</h3> 183 184<p>For bitmap assets that you draw on top of other elements, enable bitmap filtering on the same 185{@link android.graphics.Paint} instance using the {@link android.graphics.Paint#setFilterBitmap 186setFilterBitmap()} method. <a href="#fig2">Figure 2</a> shows a magnified view of a clock hand with 187and without bitmap filtering.</p> 188 189<p class="note"><strong>Note:</strong> In low-bit ambient mode, the system does not reliably 190render the colors in the image for bitmap filtering to process successfully. When ambient mode is 191active, disable bitmap filtering.</p> 192 193<h2 id="OutDrawing">Move Expensive Operations Outside the Drawing Method</h2> 194 195<p>The system calls the 196<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 197method every time it redraws your watch face, so you should only include operations that are 198strictly required to update the watch face inside this method to improve performance.<p> 199 200<p>When possible, avoid performing these operations inside the 201<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 202method:</p> 203 204<ul> 205<li>Loading images and other resources.</li> 206<li>Resizing images.</li> 207<li>Allocating objects.</li> 208<li>Performing computations whose result does not change between frames.</li> 209</ul> 210 211<p>You can usually perform these operations in the 212<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.Engine.html#onCreate(android.view.SurfaceHolder)"><code>Engine.onCreate()</code></a> 213method instead. 214You can resize images ahead of time in the {@link 215android.service.wallpaper.WallpaperService.Engine#onSurfaceChanged(android.view.SurfaceHolder, int, int, int) 216Engine.onSurfaceChanged()} method, which provides you with the size of the canvas.</p> 217 218<p>To analyze the performance of your watch face, use the Android Device Monitor. In particular, 219ensure that the execution time for your 220<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 221implementation is short and 222consistent across invocations. For more information, see 223<a href="{@docRoot}tools/debugging/ddms.html">Using DDMS</a>.</p> 224 225
