Posted by Hak Matsuda and Dirk Dougherty, Android Developer Relations team
If you develop a performance-intensive 3D game, you’re always looking for ways to give users richer graphics, higher frame rates, and better responsiveness. You also want to conserve the user’s battery and keep the device from getting too warm during play. To help you optimize in all of these areas, consider taking advantage of the hardware scaler that’s available on almost all Android devices in the market today.
Virtually all modern Android devices use a CPU/GPU chipset that includes a hardware video scaler. Android provides the higher-level integration and makes the scaler available to apps through standard Android APIs, from Java or native (C++) code. To take advantage of the hardware scaler, all you have to do is render to a fixed-size graphics buffer, rather than using the system-provided default buffers, which are sized to the device's full screen resolution.
When you render to a fixed-size buffer, the device hardware does the work of scaling your scene up (or down) to match the device's screen resolution, including making any adjustments to aspect ratio. Typically, you would create a fixed-size buffer that's smaller than the device's full screen resolution, which lets you render more efficiently — especially on today's high-resolution screens.
Using the hardware scaler is more efficient for several reasons. First, hardware scalers are extremely fast and can produce great visual results through multi-tap and other algorithms that reduce artifacts. Second, because your app is rendering to a smaller buffer, the computation load on the GPU is reduced and performance improves. Third, with less computation work to do, the GPU runs cooler and uses less battery. And finally, you can choose what size rendering buffer you want to use, and that buffer can be the same on all devices, regardless of the actual screen resolution.
In a mobile GPU, the pixel fill rate is one of the major sources of performance bottlenecks for performance game applications. With newer phones and tablets offering higher and higher screen resolutions, rendering your 2D or 3D graphics on those those devices can significantly reduce your frame rate. The GPU hits its maximum fill rate, and with so many pixels to fill, your frame rate drops.
Power consumed in the GPU at different rendering resolutions, across several popular chipsets in use on Android devices. (Data provided by Qualcomm).
To avoid these bottlenecks, you need to reduce the number of pixels that your game is drawing in each frame. There are several techniques for achieving that, such as using depth-prepass optimizations and others, but a really simple and effective way is making use of the hardware scaler.
Instead of rendering to a full-size buffer that could be as large as 2560x1600, your game can instead render to a smaller buffer — for example 1280x720 or 1920x1080 — and let the hardware scaler expand your scene without any additional cost and minimal loss in visual quality.
A performance-intensive game can tend to consume too much battery and generate too much heat. The game’s power consumption and thermal conditions are important to users, and they are important considerations to developers as well.
As shown in the diagram, the power consumed in the device GPU increases significantly as rendering resolution rises. In most cases, any heavy use of power in GPU will end up reducing battery life in the device.
In addition, as CPU/GPU rendering load increases, heat is generated that can make the device uncomfortable to hold. The heat can even trigger CPU/GPU speed adjustments designed to cool the CPU/GPU, and these in turn can throttle the processing power that’s available to your game.
For both minimizing power consumption and thermal effects, using the hardware scaler can be very useful. Because you are rendering to a smaller buffer, the GPU spends less energy rendering and generates less heat.
Android gives you easy access to the hardware scaler through standard APIs, available from your Java code or from your native (C++) code through the Android NDK.
All you need to do is use the APIs to create a fixed-size buffer and render into it. You don’t need to consider the actual size of the device screen, however in cases where you want to preserve the original aspect ratio, you can either match the aspect ratio of the buffer to that of the screen, or you can adjust your rendering into the buffer.
From your Java code, you access the scaler through SurfaceView, introduced in API level 1. Here’s how you would create a fixed-size buffer at 1280x720 resolution:
SurfaceView
surfaceView = new GLSurfaceView(this); surfaceView.getHolder().setFixedSize(1280, 720);
If you want to use the scaler from native code, you can do so through the NativeActivity class, introduced in Android 2.3 (API level 9). Here’s how you would create a fixed-size buffer at 1280x720 resolution using NativeActivity:
NativeActivity
int32_t ret = ANativeWindow_setBuffersGeometry(window, 1280, 720, 0);
By specifying a size for the buffer, the hardware scaler is enabled and you benefit in your rendering to the specified window.
If you will use a fixed-size graphics buffer, it's important to choose a size that balances visual quality across targeted devices with performance and efficiency gains.
For most performance 3D games that use the hardware scaler, the recommended size for rendering is 1080p. As illustrated in the diagram, 1080p is a sweet spot that balances a visual quality, frame rate, and power consumption. If you are satisfied with 720p, of course you can use that size for even more efficient operations.
If you’d like to take advantage of the hardware scaler in your app, take a look at the class documentation for SurfaceView or NativeActivity, depending on whether you are rendering through the Android framework or native APIs.
[This post is by Romain Guy, who likes things on your screen to move fast. —Tim Bray]
One of the biggest changes we made to Android for Honeycomb is the addition of a new rendering pipeline so that applications can benefit from hardware accelerated 2D graphics. Hardware accelerated graphics is nothing new to the Android platform, it has always been used for windows composition or OpenGL games for instance, but with this new rendering pipeline applications can benefit from an extra boost in performance. On a Motorola Xoom device, all the standard applications like Browser and Calendar use hardware-accelerated 2D graphics.
In this article, I will show you how to enable the hardware accelerated 2D graphics pipeline in your application and give you a few tips on how to use it properly.
To enable the hardware accelerated 2D graphics, open your AndroidManifest.xml file and add the following attribute to the <application /> tag:
AndroidManifest.xml
<application />
android:hardwareAccelerated="true"
If your application uses only standard widgets and drawables, this should be all you need to do. Once hardware acceleration is enabled, all drawing operations performed on a View's Canvas are performed using the GPU.
If you have custom drawing code you might need to do a bit more, which is in part why hardware acceleration is not enabled by default. And it's why you might want to read the rest of this article, to understand some of the important details of acceleration.
Because of the characteristics of the new rendering pipeline, you might run into issues with your application. Problems usually manifest themselves as invisible elements, exceptions or different-looking pixels. To help you, Android gives you 4 different ways to control hardware acceleration. You can enable or disable it on the following elements:
To enable or disable hardware acceleration at the application or activity level, use the XML attribute mentioned earlier. The following snippet enables hardware acceleration for the entire application but disables it for one activity:
<application android:hardwareAccelerated="true"> <activity ... /> <activity android:hardwareAccelerated="false" /> </application>
If you need more fine-grained control, you can enable hardware acceleration for a given window at runtime:
getWindow().setFlags( WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED, WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED);
Note that you currently cannot disable hardware acceleration at the window level. Finally, hardware acceleration can be disabled on individual views:
view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
Layer types have many other usages that will be described later.
It is sometimes useful for an application, or more likely a custom view, to know whether it currently is hardware accelerated. 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.
There are two different ways to check whether the application is hardware accelerated:
View.isHardwareAccelerated()
Canvas.isHardwareAccelerated()
If you must do this check in your drawing code, it is highly recommended to use Canvas.isHardwareAccelerated() instead of View.isHardwareAccelerated(). Indeed, even when a View is attached to a hardware accelerated window, it can be drawn using a non-hardware accelerated Canvas. This happens for instance when drawing a View into a bitmap for caching purpose.
The current hardware accelerated 2D pipeline supports the most commonly used Canvas operations, and then some. We implemented all the operations needed to render the built-in applications, all the default widgets and layouts, and common advanced visual effects (reflections, tiled textures, etc.) There are however a few operations that are currently not supported, but might be in a future version of Android:
clipPath
clipRegion
drawPicture
drawPoints
drawPosText
drawTextOnPath
drawVertices
setLinearText
setMaskFilter
setRasterizer
In addition, some operations behave differently when hardware acceleration enabled:
clipRect
XOR
Difference
ReverseDifference
drawBitmapMesh
drawLines
setDrawFilter
setDither
setFilterBitmap
setShadowLayer
ComposeShader
BitmapShader
LinearGradientShader
If drawing code in one of your views is affected by any of the missing features or limitations, you don't have to miss out on the advantages of hardware acceleration for your overall application. Instead, consider rendering the problematic view into a bitmap or setting its layer type to LAYER_TYPE_SOFTWARE. In both cases, you will switch back to the software rendering pipeline.
LAYER_TYPE_SOFTWARE
Switching to hardware accelerated 2D graphics is a great way to get smoother animations and faster rendering in your application but it is by no means a magic bullet. Your application should be designed and implemented to be GPU friendly. It is easier than you might think if you follow these recommendations:
View.setAlpha()
AlphaAnimation
ObjectAnimator
LAYER_TYPE_HARDWARE
Since Android 1.0, Views have had the ability to render into off-screen buffers, either by using a View's drawing cache, or by using Canvas.saveLayer(). Off-screen buffers, or layers, have several interesting usages. They can be used to get better performance when animating complex Views or to apply composition effects. For instance, fade effects are implemented by using Canvas.saveLayer() to temporarily render a View into a layer and then compositing it back on screen with an opacity factor.
Canvas.saveLayer()
Because layers are so useful, Android 3.0 gives you more control on how and when to use them. To to so, we have introduced a new API called View.setLayerType(int type, Paint p). This API takes two parameters: the type of layer you want to use and an optional Paint that describes how the layer should be composited. The paint parameter may be used to apply color filters, special blending modes or opacity to a layer. A View can use one of 3 layer types:
View.setLayerType(int type, Paint p)
LAYER_TYPE_NONE
The type of layer you will use depends on your goal:
invalidate()
ColorMatrixColorFilter
Hardware-accelerated 2D graphics help deliver a faster and smoother user experience, especially when it comes to animations. Running an animation at 60 frames per second is not always possible when animating complex views that issue a lot of drawing operations. 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.
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. Here is the list of properties that will affect the way the layer is composited; calling the setter for any of these properties will result in optimal invalidation and no redraw of the targeted View:
alpha
x
y
translationX
translationY
scaleX
scaleY
rotation
rotationX
rotationY
pivotX
pivotY
These properties are the names used when animating a View with an ObjectAnimator. If you want to set/get these properties, call the appropriate setter or getter. For instance, to modify the alpha property, call setAlpha(). The following code snippet shows the most efficient way to rotate a View in 3D around the Y axis:
setAlpha()
view.setLayerType(View.LAYER_TYPE_HARDWARE, null); ObjectAnimator.ofFloat(view, "rotationY", 180).start();
Since hardware layers consume video memory, it is highly recommended you enable them only for the duration of the animation. This can be achieved with animation listeners:
view.setLayerType(View.LAYER_TYPE_HARDWARE, null); ObjectAnimator animator = ObjectAnimator.ofFloat( view, "rotationY", 180); animator.addListener(new AnimatorListenerAdapter() { @Override public void onAnimationEnd(Animator animation) { view.setLayerType(View.LAYER_TYPE_NONE, null); } }); animator.start();
Along with hardware-accelerated 2D graphics, Android 3.0 introduces another major change in the UI toolkit’s drawing model: display lists, which are only enabled when hardware acceleration is turned on. To fully understand display lists and how they may affect your application it is important to also understand how Views are drawn.
Whenever an application needs to update a part of its UI, it invokes invalidate() (or one of its variants) on any View whose content has changed. The invalidation messages are propagated all the way up the view hierarchy to compute the dirty region; the region of the screen that needs to be redrawn. The system then draws any View in the hierarchy that intersects with the dirty region. The drawing model is therefore made of two stages:
There are unfortunately two drawbacks to this approach. First, this drawing model requires execution of a lot of code on every draw pass. Imagine for instance your application calls invalidate() on a button and that button sits on top of a more complex View like a MapView. When it comes time to draw, the drawing code of the MapView will be executed even though the MapView itself has not changed.
MapView
The second issue with that approach is that it can hide bugs in your application. Since views are redrawn anytime they intersect with the dirty region, a View whose content you changed might be redrawn even though invalidate() was not called on it. When this happens, you are relying on another View getting invalidated to obtain the proper behavior. Needless to say, this behavior can change every time you modify your application ever so slightly. Remember this rule: always call invalidate() on a View whenever you modify data or state that affects this View’s drawing code. This applies only to custom code since setting standard properties, like the background color or the text in a TextView, will cause invalidate() to be called properly internally.
TextView
Android 3.0 still relies on invalidate() to request screen updates and draw() to render views. The difference is in how the drawing code is handled internally. Rather than executing the drawing commands immediately, the UI toolkit now records them inside display lists. This means that display lists do not contain any logic, but rather the output of the view hierarchy’s drawing code. Another interesting optimization is that the system only needs to record/update display lists for views marked dirty by an invalidate() call; views that have not been invalidated can be redrawn simply by re-issuing the previously recorded display list. The new drawing model now contains 3 stages:
draw()
With this model, you cannot rely on a View intersecting the dirty region to have its draw() method executed anymore: to ensure that a View’s display list will be recorded, you must call invalidate(). This kind of bug becomes very obvious with hardware acceleration turned on and is easy to fix: you would see the previous content of a View after changing it.
Using display lists also benefits animation performance. In the previous section, we saw that setting specific properties (alpha, rotation, etc.) does not require invalidating the targeted View. This optimization also applies to views with display lists (any View when your application is hardware accelerated.) Let’s imagine you want to change the opacity of a ListView embedded inside a LinearLayout, above a Button. Here is what the (simplified) display list of the LinearLayout looks like before changing the list’s opacity:
ListView
LinearLayout
Button
DrawDisplayList(ListView) DrawDisplayList(Button)
After invoking listView.setAlpha(0.5f) the display list now contains this:
listView.setAlpha(0.5f)
SaveLayerAlpha(0.5) DrawDisplayList(ListView) Restore DrawDisplayList(Button)
The complex drawing code of ListView was not executed. Instead the system only updated the display list of the much simpler LinearLayout. In previous versions of Android, or in an application without hardware acceleration enabled, the drawing code of both the list and its parent would have to be executed again.
Enabling hardware accelerated 2D graphics in your application is easy, particularly if you rely solely on standard views and drawables. Just keep in mind the few limitations and potential issues described in this document and make sure to thoroughly test your application!
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