GPU硬件加速相关

从android3.0开始，2D渲染开始支持硬件加速，即在view的Canvas上的绘图操作可以用GPU来加速。

硬件加速会使app消耗更多的内存。

如果配置文件中，Target API level >=14 硬件加速是默认开启的。

如果应用只是使用了标准的 view 和 drawable ，那么对app开启全局的硬件加速不会有什么问题。但由于硬件加速并非支持所有的2d绘图操作，所以对使用了自定义的view和drawable，可能会产生不利的影响。比如view不见了，异常，或者渲染不正确等。要在实际的设备上测试。

可在这几个级别控制是否支持硬件加速：

Application

Activity

Window

View

1. 在Applciation级别控制硬件加速：

<application android:hardwareAccelerated="true" ...>

2. Activity级别对单个的Activity控制是否启用硬件加速：

下面的例子在整个应用中启用了硬加速但对某个activity禁止了硬加速：

<application android:hardwareAccelerated="true">
    <activity ... />
    <activity android:hardwareAccelerated="false" />
</application>

3. Window级别(Added in API level 11) (现在对window级别只能开启不能禁用硬件加速)

 getWindow().setFlags(
    WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED,
    WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED);

4. View级别可以在View级别禁用硬件加速。(注：当前不能在View级别启用硬加速．)

myView.setLayerType(View.LAYER_TYPE_SOFTWARE, null); (Added in API level 11)

或者使用android:layerType="software"来关闭硬件加速：

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:paddingLeft="2dp"
    android:layerType="software"
    android:paddingRight="2dp" >

1)LAYER_TYPE_NONE: The view is rendered normally and is not backed by an off-screen buffer. This is the default behavior.

2)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 LAYER_TYPE_SOFTWARE.

3)LAYER_TYPE_SOFTWARE: The view is rendered in software into a bitmap. The type of layer you use depends on your goal: Performance: 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 invalidate(). Some animations, such as alpha animations, can then be applied directly onto the layer, which is very efficient for the GPU to do.

Visual effects: Use a hardware or software layer type and a Paint to apply special visual treatments to a view. For instance, you can draw a view in black and white using a ColorMatrixColorFilter.

Compatibility: 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.

如何判断一个View是否启用了硬件加速

View.isHardwareAccelerated() returns true if the View is attached to a hardware accelerated window. Canvas.isHardwareAccelerated() returns true if the Canvas is hardware accelerated

如果必须在你的绘制代码中做这个判断，应使用Canvas.isHardwareAccelerated() 而不是View.isHardwareAccelerated()．因为当一个view附加到一个硬加速的window上，它仍可以使用非硬件速的Canvas进行绘制操作．比如当为了高速缓存而把一个view画到一个bitmap中．

硬件加速可以提高View的动画效率，避免在动画的过程中，不停的重绘自己。 View只有在手动调用invalidate()，或者调用了改变属性的方法，而这个方法又导致了invalidate()的调用时，才会重绘。

http://developer.android.com/guide/topics/graphics/hardware-accel.html#

http://blog.csdn.net/lovehankuo/article/details/9714927

http://blog.csdn.net/internetman/article/details/7098363

并非所有的2D绘图操作都支持硬件加速：