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="#ReduceSize">Reduce the Size of Your Bitmap Assets</a></li> 10 <li><a href="#CombineBitmaps">Combine Bitmap Assets</a></li> 11 <li><a href="#AntiAlias">Disable Anti-Aliasing when Drawing Scaled Bitmaps</a></li> 12 <li><a href="#OutDrawing">Move Expensive Operations Outside the Drawing Method</a></li> 13 <li><a href="#SavePower">Follow Best Practices to Save Power</a></li> 14</ol> 15<h2>You should also read</h2> 16<ul> 17 <li><a href="{@docRoot}design/wear/watchfaces.html">Watch Faces for Android Wear</a></li> 18</ul> 19</div> 20</div> 21 22<p>In addition to accommodating notification cards and system indicators, you need to ensure that 23the animations in your watch face run smoothly and that your service does not perform unnecessary 24computations. Watch faces in Android Wear run continuously on the device, so it is critical 25that your watch face uses power efficiently.</p> 26 27<p>This lesson provides some tips to speed up your animations and to measure and conserve 28power on the device.</p> 29 30 31 32<h2 id="ReduceSize">Reduce the Size of Your Bitmap Assets</h2> 33 34<p>Many watch faces consist of a background image and other graphic assets that are transformed 35and overlapped on top of the background image, such as clock hands and other elements of the design 36that move over time. Typically these graphic elements are rotated (and sometimes scaled) inside the 37<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 38method every time the system redraws the watch face, as described in 39<a href="{@docRoot}training/wearables/watch-faces/drawing.html#Drawing">Draw Your Watch 40Face</a>.</p> 41 42<p>The larger these graphic assets are, the more computationally expensive it is to transform them. 43Transforming large graphic assets in the 44<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 45method drastically reduces the frame rate at which the system can run your animations.</p> 46 47<div id="fig1" style="float:right;width:250px;margin-left:25px"> 48<img src="{@docRoot}training/wearables/watch-faces/images/ClockHandFull.png" alt="" 49 width="180" height="180"/> 50<img src="{@docRoot}training/wearables/watch-faces/images/ClockHandCropped.png" alt="" 51 width="15" height="65" style="margin-left:25px"/> 52<p class="img-caption"> 53<strong>Figure 1.</strong> Clock hands can be cropped to remove extra pixels.</p> 54</div> 55 56<p>To improve the performance of your watch face:</p> 57 58<ul> 59<li>Do not use graphic elements that are larger than you need.</li> 60<li>Remove extra transparent pixels around the edges.</li> 61</ul> 62 63<p>The example clock hand on the left side of <a href="#fig1">Figure 1</a> can be reduced in size 64by 97%.</p> 65 66<p>Reducing the size of your bitmap assets as described in this section not only improves 67the performance of your animations, but it also saves power.</p> 68 69 70 71<h2 id="CombineBitmaps">Combine Bitmap Assets</h2> 72 73<p>If you have bitmaps that are often drawn together, consider combining them into the same 74graphic asset. You can often combine the background image in interactive mode with the tick 75marks to avoid drawing two full-screen bitmaps every time the system redraws the watch face.</p> 76 77 78 79<h2 id="AntiAlias">Disable Anti-Aliasing when Drawing Scaled Bitmaps</h2> 80 81<p>When you draw a scaled bitmap on the {@link android.graphics.Canvas} object using the {@link 82android.graphics.Canvas#drawBitmap(android.graphics.Bitmap, float, float, android.graphics.Paint) 83Canvas.drawBitmap()} method, you can provide a {@link android.graphics.Paint} instance to configure 84several options. To improve performance, disable anti-aliasing using the {@link 85android.graphics.Paint#setAntiAlias setAntiAlias()} method, since this option does not have any 86effect on bitmaps.</p> 87 88<div id="fig2" style="float:right;width:250px;margin-left:40px;margin-top:12px"> 89<img src="{@docRoot}training/wearables/watch-faces/images/BitmapFilterDisabled.png" alt="" 90 width="70" height="70" style="margin-left:20px"/> 91<img src="{@docRoot}training/wearables/watch-faces/images/BitmapFilterEnabled.png" alt="" 92 width="70" height="70" style="margin-left:20px"/> 93<p class="img-caption"><strong>Figure 2.</strong> Example of bitmap filtering disabled (left) and 94enabled (right).</p> 95</div> 96 97<h3 id="BitmapFiltering">Use bitmap filtering</h3> 98 99<p>For bitmap assets that you draw on top of other elements, enable bitmap filtering on the same 100{@link android.graphics.Paint} instance using the {@link android.graphics.Paint#setFilterBitmap 101setFilterBitmap()} method. <a href="#fig2">Figure 2</a> shows a magnified view of a clock hand with 102and without bitmap filtering.</p> 103 104<p class="note"><strong>Note:</strong> In low-bit ambient mode, the system does not reliably 105render the colors in the image for bitmap filtering to process successfully. When ambient mode is 106active, disable bitmap filtering.</p> 107 108<h2 id="OutDrawing">Move Expensive Operations Outside the Drawing Method</h2> 109 110<p>The system calls the 111<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 112method every time it redraws your watch face, so you should only include operations that are 113strictly required to update the watch face inside this method to improve performance.<p> 114 115<p>When possible, avoid performing these operations inside the 116<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 117method:</p> 118 119<ul> 120<li>Loading images and other resources.</li> 121<li>Resizing images.</li> 122<li>Allocating objects.</li> 123<li>Performing computations whose result does not change between frames.</li> 124</ul> 125 126<p>You can usually perform these operations in the 127<a href="{@docRoot}reference/android/support/wearable/watchface/WatchFaceService.Engine.html#onCreate(android.view.SurfaceHolder)"><code>Engine.onCreate()</code></a> 128method instead. 129You can resize images ahead of time in the {@link 130android.service.wallpaper.WallpaperService.Engine#onSurfaceChanged(android.view.SurfaceHolder, int, int, int) 131Engine.onSurfaceChanged()} method, which provides you with the size of the canvas.</p> 132 133<p>To analyze the performance of your watch face, use the Android Device Monitor. In particular, 134ensure that the execution time for your 135<a href="{@docRoot}reference/android/support/wearable/watchface/CanvasWatchFaceService.Engine.html#onDraw(android.graphics.Canvas, android.graphics.Rect)"><code>Engine.onDraw()</code></a> 136implementation is short and 137consistent across invocations. For more information, see 138<a href="{@docRoot}tools/debugging/ddms.html">Using DDMS</a>.</p> 139 140 141 142<h2 id="SavePower">Follow Best Practices to Save Power</h2> 143 144<p>In addition to the techniques described in the previous sections, follow the best 145practices in this section to reduce the power consumption of your watch face.</p> 146 147<h3>Reduce the frame rate of animations</h3> 148 149<p>Animations are often computationally expensive and consume a significant amount of power. Most 150animations look fluid at 30 frames per second, so you should avoid running your animations 151at a higher frame rate.</p> 152 153<h3>Let the CPU sleep</h3> 154 155<p>Animations and small changes to the contents of the watch face wake up the CPU. Your watch 156face should let the CPU sleep in between animations. For example, you can use short bursts of 157animation every second in interactive mode and then let the CPU sleep until the next second. 158Letting the CPU sleep often, even briefly, can significantly reduce power consumption.</p> 159 160<p>To maximize battery life, use animations sparingly. Even a blinking colon wakes up the CPU with 161every blink and hurts battery life.</p> 162 163<h3>Monitor power consumption</h3> 164 165<p>The <a href="https://play.google.com/store/apps/details?id=com.google.android.wearable.app&hl=en"> 166Android Wear companion app</a> lets developers and users see how much battery different processes 167on the wearable device are consuming under <strong>Settings</strong> > <strong>Watch 168battery</strong>.</p> 169 170<p>For more information about new features in Android 5.0 that help you improve battery life, 171see <a href="{@docRoot}about/versions/android-5.0.html#Power">Project Volta</a>.</p> 172
