volume down + power key ScreenShot 流程

chipset: MSM8x25Q

codebase: Android 4.1

interceptKeyBeforeQueueing ->	PhoneWindowManager.java
	interceptScreenshotChord ->
		postDelayed ->
			takeScreenshot -> 
				handleMessage -> TakeScreenshotService.java
					screenshot ->  GlobalScreenshot.java
						screenshot -> Surface.java
							Surface_screenshotAll -> android_view_surface.cpp
								doScreenshot ->
									update ->
										update -> SurfaceComposerClient.cpp
											captureScreen -> SurfaceFlinger.cpp
												handler -> 
													captureScreenImplLocked 	//将重新绘制得到的显示数据保存到base中

如果发现屏幕反向180°之后，可以做如下修改,  system property 可以定义在system.prop中。

    void takeScreenshot(Runnable finisher, boolean statusBarVisible, boolean navBarVisible) {
~~snip

        // We need to orient the screenshot correctly (and the Surface api seems to take screenshots
        // only in the natural orientation of the device :!)
        mDisplay.getRealMetrics(mDisplayMetrics);
        float[] dims = {mDisplayMetrics.widthPixels, mDisplayMetrics.heightPixels};
		
/*Kris.Fei, 20130208, WMS dose not know we rotate the layer in SF. {*/
        float degrees;
        if (SystemProperties.getInt("debug.sf.hwrotation",0) == 180) {
            degrees = getDegreesForRotation(Surface.ROTATION_180);
            Slog.e("Rotation", "Screenshot with 180 degree rotation.");
        } else {
            degrees = getDegreesForRotation(mDisplay.getRotation());
        }
/*Kris.Fei, 20130208, WMS dose not know we rotate the layer in SF. }*/
		
        boolean requiresRotation = (degrees > 0);
~~snip
}