Android系统截屏的实现分析
先来看看别个总结的流程(自己本来想画个，发现找到个就不造车了)
（该图引自http://blog.csdn.net/hk_256/article/details/7306590）
源码部分
喔 对鸟，这个是5.1的代码，kk的没有研究过，想必也差不多
interceptKeyBeforeQueueing()拦截按键信息
interceptScreenshotChord()：handler调用截屏
private void interceptScreenshotChord() {
if (mScreenshotChordEnabled
&& mScreenshotChordVolumeDownKeyTriggered && mScreenshotChordPowerKeyTriggered
&& !mScreenshotChordVolumeUpKeyTriggered) {
final long now = SystemClock.uptimeMillis();
if (now <= mScreenshotChordVolumeDownKeyTime + SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS
&& now <= mScreenshotChordPowerKeyTime
+ SCREENSHOT_CHORD_DEBOUNCE_DELAY_MILLIS) {
mScreenshotChordVolumeDownKeyConsumed = true;
cancelPendingPowerKeyAction();
mHandler.postDelayed(mScreenshotRunnable, getScreenshotChordLongPressDelay());
}
}
}
private final Runnable mScreenshotRunnable = new Runnable() {
@Override
public void run() {
takeScreenshot();
}
};private void takeScreenshot() {
synchronized (mScreenshotLock) {
if (mScreenshotConnection != null) {
return;
}
ComponentName cn = new ComponentName("com.android.systemui",
"com.android.systemui.screenshot.TakeScreenshotService");//实际上是通过启动systemui的TakeScreenshotServiceservice来实现
Intent intent = new Intent();
intent.setComponent(cn);
ServiceConnection conn = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
synchronized (mScreenshotLock) {
if (mScreenshotConnection != this) {
return;
}
Messenger messenger = new Messenger(service);
Message msg = Message.obtain(null, 1);
final ServiceConnection myConn = this;
Handler h = new Handler(mHandler.getLooper()) {
@Override
public void handleMessage(Message msg) {
synchronized (mScreenshotLock) {
if (mScreenshotConnection == myConn) {
mContext.unbindService(mScreenshotConnection);
mScreenshotConnection = null;
mHandler.removeCallbacks(mScreenshotTimeout);
}
}
}
};
msg.replyTo = new Messenger(h);
msg.arg1 = msg.arg2 = 0;
if (mStatusBar != null && mStatusBar.isVisibleLw())
msg.arg1 = 1;
if (mNavigationBar != null && mNavigationBar.isVisibleLw())
msg.arg2 = 1;
try {
messenger.send(msg);
} catch (RemoteException e) {
}
}
}
@Override
public void onServiceDisconnected(ComponentName name) {}
};
if (mContext.bindServiceAsUser(
intent, conn, Context.BIND_AUTO_CREATE, UserHandle.CURRENT)) {
mScreenshotConnection = conn;
mHandler.postDelayed(mScreenshotTimeout, 10000);
}
}
}public class TakeScreenshotService extends Service {
private static final String TAG = "TakeScreenshotService";
private static GlobalScreenshot mScreenshot;
private Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
final Messenger callback = msg.replyTo;
if (mScreenshot == null) {
mScreenshot = new GlobalScreenshot(TakeScreenshotService.this);
}
mScreenshot.takeScreenshot(new Runnable() {
@Override public void run() {
Message reply = Message.obtain(null, 1);
try {
callback.send(reply);
} catch (RemoteException e) {
}
}
}, msg.arg1 > 0, msg.arg2 > 0);//这个方法执行截屏，以及window的ui效果等
}
}
};
@Override
public IBinder onBind(Intent intent) {
return new Messenger(mHandler).getBinder();
}
}
在SurfaceControl类中，在这儿调用底层nativeScreenshot方法截屏
/**
* Like {@link SurfaceControl#screenshot(int, int, int, int, boolean)} but
* with builtInDisplayId in the screenshot.
*
* @param width The desired width of the returned bitmap; the raw
* screen will be scaled down to this size.
* @param height The desired height of the returned bitmap; the raw
* screen will be scaled down to this size.
* @param builtInDisplayId The Built-in physical display id.
* @return Returns a Bitmap containing the screen contents, or null
* if an error occurs. Make sure to call Bitmap.recycle() as soon as
* possible, once its content is not needed anymore.
*
* @hide
*/
public static Bitmap screenshot(int width, int height, int builtInDisplayId) {
IBinder displayToken = SurfaceControl.getBuiltInDisplay(builtInDisplayId);
Log.d(TAG, "screenshot, builtInDisplayId = " + builtInDisplayId);
return nativeScreenshot(displayToken, new Rect(), width, height, 0, 0, true,
false, Surface.ROTATION_0);
}
static void nativeScreenshot(JNIEnv* env, jclass clazz, jobject displayTokenObj,
jobject surfaceObj, jobject sourceCropObj, jint width, jint height,
jint minLayer, jint maxLayer, bool allLayers, bool useIdentityTransform) {
sp displayToken = ibinderForJavaObject(env, displayTokenObj);
if (displayToken != NULL) {
sp consumer = android_view_Surface_getSurface(env, surfaceObj);
if (consumer != NULL) {
int left = env->GetIntField(sourceCropObj, gRectClassInfo.left);
int top = env->GetIntField(sourceCropObj, gRectClassInfo.top);
int right = env->GetIntField(sourceCropObj, gRectClassInfo.right);
int bottom = env->GetIntField(sourceCropObj, gRectClassInfo.bottom);
Rect sourceCrop(left, top, right, bottom);
if (allLayers) {
minLayer = 0;
maxLayer = -1;
}
ScreenshotClient::capture(displayToken,
consumer->getIGraphicBufferProducer(), sourceCrop,
width, height, uint32_t(minLayer), uint32_t(maxLayer),
useIdentityTransform);
}
}
} 再往下
status_t ScreenshotClient::capture(
const sp& display,
const sp& producer,
Rect sourceCrop, uint32_t reqWidth, uint32_t reqHeight,
uint32_t minLayerZ, uint32_t maxLayerZ, bool useIdentityTransform) {
sp s(ComposerService::getComposerService());
if (s == NULL) return NO_INIT;
return s->captureScreen(display, producer, sourceCrop,
reqWidth, reqHeight, minLayerZ, maxLayerZ, useIdentityTransform);
} 再找找
virtual status_t captureScreen(const sp& display,
const sp& producer,
Rect sourceCrop, uint32_t reqWidth, uint32_t reqHeight,
uint32_t minLayerZ, uint32_t maxLayerZ,
bool useIdentityTransform,
ISurfaceComposer::Rotation rotation)
{
Parcel data, reply;
data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor());
data.writeStrongBinder(display);
data.writeStrongBinder(producer->asBinder());
data.write(sourceCrop);
data.writeInt32(reqWidth);
data.writeInt32(reqHeight);
data.writeInt32(minLayerZ);
data.writeInt32(maxLayerZ);
data.writeInt32(static_cast(useIdentityTransform));
data.writeInt32(static_cast(rotation));
remote()->transact(BnSurfaceComposer::CAPTURE_SCREEN, data, &reply);
return reply.readInt32();
} 搬个源码做个笔记
再往下就是涉及底层buffer之类的处理了=。=