// frameworks/base/core/java/android/hardware/display/DisplayManager.java
public VirtualDisplay createVirtualDisplay(@NonNull String name,
		int width, int height, int densityDpi, @Nullable Surface surface, int flags) {
}
public VirtualDisplay createVirtualDisplay(@NonNull String name,
		int width, int height, int densityDpi, @Nullable Surface surface, int flags,
		@Nullable VirtualDisplay.Callback callback, @Nullable Handler handler) {
}
/** @hide */
public VirtualDisplay createVirtualDisplay(@Nullable MediaProjection projection,
		@NonNull String name, int width, int height, int densityDpi, @Nullable Surface surface,
		int flags, @Nullable VirtualDisplay.Callback callback, @Nullable Handler handler,
		@Nullable String uniqueId) {
}
/** @hide */
public VirtualDisplay createVirtualDisplay(@Nullable MediaProjection projection,
		@NonNull VirtualDisplayConfig virtualDisplayConfig,
		@Nullable VirtualDisplay.Callback callback, @Nullable Handler handler) {
}

// frameworks/base/media/java/android/media/projection/MediaProjection.java
    public VirtualDisplay createVirtualDisplay(@NonNull VirtualDisplayConfig virtualDisplayConfig,
            @Nullable VirtualDisplay.Callback callback, @Nullable Handler handler) {
        DisplayManager dm = mContext.getSystemService(DisplayManager.class);
        // 調(diào)用DisplayManager的接口
        return dm.createVirtualDisplay(this, virtualDisplayConfig, callback, handler);
    }

// frameworks/base/packages/SystemUI/tests/src/com/android/systemui/navigationbar/NavigationBarButtonTest.java
private Display createVirtualDisplay() {
	final String displayName = "NavVirtualDisplay";
	final DisplayInfo displayInfo = new DisplayInfo();
	mContext.getDisplay().getDisplayInfo(displayInfo);
	final DisplayManager displayManager = mContext.getSystemService(DisplayManager.class);
	// 創(chuàng)建ImageReader，通過(guò)它得到一張Surface
	mReader = ImageReader.newInstance(displayInfo.logicalWidth,
			displayInfo.logicalHeight, PixelFormat.RGBA_8888, 2);
	assertNotNull("ImageReader must not be null", mReader);
	// 創(chuàng)建虛擬屏，傳入Surface。
	mVirtualDisplay = displayManager.createVirtualDisplay(displayName, displayInfo.logicalWidth,
			displayInfo.logicalHeight, displayInfo.logicalDensityDpi, mReader.getSurface(),
			0 /*flags*/);
	assertNotNull("virtual display must not be null", mVirtualDisplay);
	waitForDisplayReady(mVirtualDisplay.getDisplay().getDisplayId());
	return mVirtualDisplay.getDisplay();
}

    public static final int VIRTUAL_DISPLAY_FLAG_PUBLIC = 1 << 0;
    public static final int VIRTUAL_DISPLAY_FLAG_PRESENTATION = 1 << 1;
    public static final int VIRTUAL_DISPLAY_FLAG_SECURE = 1 << 2;
    public static final int VIRTUAL_DISPLAY_FLAG_OWN_CONTENT_ONLY = 1 << 3;
    public static final int VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR = 1 << 4;
    public static final int VIRTUAL_DISPLAY_FLAG_CAN_SHOW_WITH_INSECURE_KEYGUARD = 1 << 5;
    public static final int VIRTUAL_DISPLAY_FLAG_SUPPORTS_TOUCH = 1 << 6;
    public static final int VIRTUAL_DISPLAY_FLAG_ROTATES_WITH_CONTENT = 1 << 7;
    public static final int VIRTUAL_DISPLAY_FLAG_DESTROY_CONTENT_ON_REMOVAL = 1 << 8;
    public static final int VIRTUAL_DISPLAY_FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS = 1 << 9;
    public static final int VIRTUAL_DISPLAY_FLAG_TRUSTED = 1 << 10;
    public static final int VIRTUAL_DISPLAY_FLAG_OWN_DISPLAY_GROUP = 1 << 11;

    public static abstract class Callback {
        /**
         * Called when the virtual display video projection has been
         * paused by the system or when the surface has been detached
         * by the application by calling setSurface(null).
         * The surface will not receive any more buffers while paused.
         */
         public void onPaused() { }
        /**
         * Called when the virtual display video projection has been
         * resumed after having been paused.
         */
         public void onResumed() { }
        /**
         * Called when the virtual display video projection has been
         * stopped by the system.  It will no longer receive frames
         * and it will never be resumed.  It is still the responsibility
         * of the application to release() the virtual display.
         */
        public void onStopped() { }
    }

// /frameworks/base/core/java/android/hardware/display/DisplayManager.java
public VirtualDisplay createVirtualDisplay(@NonNull String name,
		int width, int height, int densityDpi, @Nullable Surface surface, int flags) {
	return createVirtualDisplay(name, width, height, densityDpi, surface, flags, null, null);
}
public VirtualDisplay createVirtualDisplay(@NonNull String name,
		int width, int height, int densityDpi, @Nullable Surface surface, int flags,
		@Nullable VirtualDisplay.Callback callback, @Nullable Handler handler) {
	final VirtualDisplayConfig.Builder builder = new VirtualDisplayConfig.Builder(name, width,
			height, densityDpi);
	builder.setFlags(flags);
	if (surface != null) {
		builder.setSurface(surface);
	}
	return createVirtualDisplay(null /* projection */, builder.build(), callback, handler);
}
// TODO : Remove this hidden API after remove all callers. (Refer to MultiDisplayService)
/** @hide */
public VirtualDisplay createVirtualDisplay(@Nullable MediaProjection projection,
		@NonNull String name, int width, int height, int densityDpi, @Nullable Surface surface,
		int flags, @Nullable VirtualDisplay.Callback callback, @Nullable Handler handler,
		@Nullable String uniqueId) {
	final VirtualDisplayConfig.Builder builder = new VirtualDisplayConfig.Builder(name, width,
			height, densityDpi);
	builder.setFlags(flags);
	if (uniqueId != null) {
		builder.setUniqueId(uniqueId);
	}
	if (surface != null) {
		builder.setSurface(surface);
	}
	return createVirtualDisplay(projection, builder.build(), callback, handler);
}
/** @hide */
public VirtualDisplay createVirtualDisplay(@Nullable MediaProjection projection,
		@NonNull VirtualDisplayConfig virtualDisplayConfig,
		@Nullable VirtualDisplay.Callback callback, @Nullable Handler handler) {
	// 走的這里，會(huì)調(diào)用到DisplayManagerGlobal中。
	return mGlobal.createVirtualDisplay(mContext, projection, virtualDisplayConfig, callback,
			handler);
}

// /frameworks/base/core/java/android/hardware/display/DisplayManager.java
public VirtualDisplay createVirtualDisplay(@NonNull Context context, MediaProjection projection,
		@NonNull VirtualDisplayConfig virtualDisplayConfig, VirtualDisplay.Callback callback,
		Handler handler) {
	VirtualDisplayCallback callbackWrapper = new VirtualDisplayCallback(callback, handler);
	// 從MediaProjection過(guò)來(lái)的調(diào)用，這個(gè)地方非空。
	IMediaProjection projectionToken = projection != null ? projection.getProjection() : null;
	int displayId;
	try {
		// 告知DMS創(chuàng)建虛擬屏，并返回DisplayID
		displayId = mDm.createVirtualDisplay(virtualDisplayConfig, callbackWrapper,
				projectionToken, context.getPackageName());
	} catch (RemoteException ex) {
		throw ex.rethrowFromSystemServer();
	}
	if (displayId < 0) {
		Log.e(TAG, "Could not create virtual display: " + virtualDisplayConfig.getName());
		return null;
	}
	// 通過(guò)DisplayID，取得Display對(duì)象信息（也是調(diào)用DMS得到的）
	Display display = getRealDisplay(displayId);
	if (display == null) {
		Log.wtf(TAG, "Could not obtain display info for newly created "
				+ "virtual display: " + virtualDisplayConfig.getName());
		try {
			// 創(chuàng)建失敗，需要釋放
			mDm.releaseVirtualDisplay(callbackWrapper);
		} catch (RemoteException ex) {
			throw ex.rethrowFromSystemServer();
		}
		return null;
	}
	// 創(chuàng)建VirtualDisplay
	return new VirtualDisplay(this, display, callbackWrapper,
			virtualDisplayConfig.getSurface());
}

// /frameworks/base/services/core/java/com/android/server/display/DisplayManagerService.java
@Override // Binder call
public int createVirtualDisplay(VirtualDisplayConfig virtualDisplayConfig,
		IVirtualDisplayCallback callback, IMediaProjection projection, String packageName) {
	// 檢查uid與包名，是否相符。
	final int callingUid = Binder.getCallingUid();
	if (!validatePackageName(callingUid, packageName)) {
		throw new SecurityException("packageName must match the calling uid");
	}
	if (callback == null) {
		throw new IllegalArgumentException("appToken must not be null");
	}
	if (virtualDisplayConfig == null) {
		throw new IllegalArgumentException("virtualDisplayConfig must not be null");
	}
	//  拿到client端傳過(guò)來(lái)的surface對(duì)象
	final Surface surface = virtualDisplayConfig.getSurface();
	int flags = virtualDisplayConfig.getFlags();
	if (surface != null && surface.isSingleBuffered()) {
		throw new IllegalArgumentException("Surface can't be single-buffered");
	}
	// 下面開(kāi)始針對(duì)Flag，做一些邏輯判斷。
	if ((flags & VIRTUAL_DISPLAY_FLAG_PUBLIC) != 0) {
		flags |= VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR;
		// Public displays can't be allowed to show content when locked.
		if ((flags & VIRTUAL_DISPLAY_FLAG_CAN_SHOW_WITH_INSECURE_KEYGUARD) != 0) {
			throw new IllegalArgumentException(
					"Public display must not be marked as SHOW_WHEN_LOCKED_INSECURE");
		}
	}
	if ((flags & VIRTUAL_DISPLAY_FLAG_OWN_CONTENT_ONLY) != 0) {
		flags &= ~VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR;
	}
	if ((flags & VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR) != 0) {
		flags &= ~VIRTUAL_DISPLAY_FLAG_OWN_DISPLAY_GROUP;
	}
	if (projection != null) {
		try {
			if (!getProjectionService().isValidMediaProjection(projection)) {
				throw new SecurityException("Invalid media projection");
			}
			flags = projection.applyVirtualDisplayFlags(flags);
		} catch (RemoteException e) {
			throw new SecurityException("unable to validate media projection or flags");
		}
	}
	if (callingUid != Process.SYSTEM_UID &&
			(flags & VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR) != 0) {
		if (!canProjectVideo(projection)) {
			throw new SecurityException("Requires CAPTURE_VIDEO_OUTPUT or "
					+ "CAPTURE_SECURE_VIDEO_OUTPUT permission, or an appropriate "
					+ "MediaProjection token in order to create a screen sharing virtual "
					+ "display.");
		}
	}
	if (callingUid != Process.SYSTEM_UID && (flags & VIRTUAL_DISPLAY_FLAG_SECURE) != 0) {
		if (!canProjectSecureVideo(projection)) {
			throw new SecurityException("Requires CAPTURE_SECURE_VIDEO_OUTPUT "
					+ "or an appropriate MediaProjection token to create a "
					+ "secure virtual display.");
		}
	}
	if (callingUid != Process.SYSTEM_UID && (flags & VIRTUAL_DISPLAY_FLAG_TRUSTED) != 0) {
		if (!checkCallingPermission(ADD_TRUSTED_DISPLAY, "createVirtualDisplay()")) {
			EventLog.writeEvent(0x534e4554, "162627132", callingUid,
					"Attempt to create a trusted display without holding permission!");
			throw new SecurityException("Requires ADD_TRUSTED_DISPLAY permission to "
					+ "create a trusted virtual display.");
		}
	}
	if (callingUid != Process.SYSTEM_UID
			&& (flags & VIRTUAL_DISPLAY_FLAG_OWN_DISPLAY_GROUP) != 0) {
		if (!checkCallingPermission(ADD_TRUSTED_DISPLAY, "createVirtualDisplay()")) {
			throw new SecurityException("Requires ADD_TRUSTED_DISPLAY permission to "
					+ "create a virtual display which is not in the default DisplayGroup.");
		}
	}
	if ((flags & VIRTUAL_DISPLAY_FLAG_TRUSTED) == 0) {
		flags &= ~VIRTUAL_DISPLAY_FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS;
	}
	// Sometimes users can have sensitive information in system decoration windows. An app
	// could create a virtual display with system decorations support and read the user info
	// from the surface.
	// We should only allow adding flag VIRTUAL_DISPLAY_FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS
	// to trusted virtual displays.
	final int trustedDisplayWithSysDecorFlag =
			(VIRTUAL_DISPLAY_FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS
					| VIRTUAL_DISPLAY_FLAG_TRUSTED);
	if ((flags & trustedDisplayWithSysDecorFlag)
			== VIRTUAL_DISPLAY_FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS
			&& !checkCallingPermission(INTERNAL_SYSTEM_WINDOW, "createVirtualDisplay()")) {
			throw new SecurityException("Requires INTERNAL_SYSTEM_WINDOW permission");
	}
	final long token = Binder.clearCallingIdentity();
	try {
		// 調(diào)用內(nèi)部實(shí)現(xiàn)
		return createVirtualDisplayInternal(callback, projection, callingUid, packageName,
				surface, flags, virtualDisplayConfig);
	} finally {
		Binder.restoreCallingIdentity(token);
	}
}
// /frameworks/base/services/core/java/com/android/server/display/DisplayManagerService.java
private int createVirtualDisplayInternal(IVirtualDisplayCallback callback,
		IMediaProjection projection, int callingUid, String packageName, Surface surface,
		int flags, VirtualDisplayConfig virtualDisplayConfig) {
	synchronized (mSyncRoot) {
		if (mVirtualDisplayAdapter == null) {
			Slog.w(TAG, "Rejecting request to create private virtual display "
					+ "because the virtual display adapter is not available.");
			return -1;
		}
		// 為虛擬屏創(chuàng)建Device（告知surfaceflinger創(chuàng)建Display）
		DisplayDevice device = mVirtualDisplayAdapter.createVirtualDisplayLocked(
				callback, projection, callingUid, packageName, surface, flags,
				virtualDisplayConfig);
		if (device == null) {
			return -1;
		}
		// 發(fā)送添加Device通知，這里比較重要
		mDisplayDeviceRepo.onDisplayDeviceEvent(device,
				DisplayAdapter.DISPLAY_DEVICE_EVENT_ADDED);
		// 檢查Display是否創(chuàng)建成功
		final LogicalDisplay display = mLogicalDisplayMapper.getDisplayLocked(device);
		if (display != null) {
			return display.getDisplayIdLocked();
		}
		// Something weird happened and the logical display was not created.
		Slog.w(TAG, "Rejecting request to create virtual display "
				+ "because the logical display was not created.");
		mVirtualDisplayAdapter.releaseVirtualDisplayLocked(callback.asBinder());
		mDisplayDeviceRepo.onDisplayDeviceEvent(device,
				DisplayAdapter.DISPLAY_DEVICE_EVENT_REMOVED);
	}
	return -1;
}

// /frameworks/base/services/core/java/com/android/server/display/VirtualDisplayAdapter.java
public DisplayDevice createVirtualDisplayLocked(IVirtualDisplayCallback callback,
		IMediaProjection projection, int ownerUid, String ownerPackageName, Surface surface,
		int flags, VirtualDisplayConfig virtualDisplayConfig) {
	String name = virtualDisplayConfig.getName();
	// VIRTUAL_DISPLAY_FLAG_SECURE 的用途，是判斷是否為安全的Display，這個(gè)參數(shù)會(huì)告知SurfaceFlinger
	boolean secure = (flags & VIRTUAL_DISPLAY_FLAG_SECURE) != 0;
	IBinder appToken = callback.asBinder();
	// 調(diào)用SurfaceFligner創(chuàng)建Display（Display的type是virtual）
	IBinder displayToken = mSurfaceControlDisplayFactory.createDisplay(name, secure);
	final String baseUniqueId =
			UNIQUE_ID_PREFIX + ownerPackageName + "," + ownerUid + "," + name + ",";
	final int uniqueIndex = getNextUniqueIndex(baseUniqueId);
	String uniqueId = virtualDisplayConfig.getUniqueId();
	if (uniqueId == null) {
		uniqueId = baseUniqueId + uniqueIndex;
	} else {
		uniqueId = UNIQUE_ID_PREFIX + ownerPackageName + ":" + uniqueId;
	}
	// 通過(guò)SurfaceFligner返回的displayToken，創(chuàng)建Device對(duì)象
	VirtualDisplayDevice device = new VirtualDisplayDevice(displayToken, appToken,
			ownerUid, ownerPackageName, surface, flags, new Callback(callback, mHandler),
			uniqueId, uniqueIndex, virtualDisplayConfig);
	//  放到虛擬屏的List中管理。
	mVirtualDisplayDevices.put(appToken, device);
	try {
		if (projection != null) {
			projection.registerCallback(new MediaProjectionCallback(appToken));
		}
		appToken.linkToDeath(device, 0);
	} catch (RemoteException ex) {
		mVirtualDisplayDevices.remove(appToken);
		device.destroyLocked(false);
		return null;
	}
	// Return the display device without actually sending the event indicating
	// that it was added.  The caller will handle it.
	return device;
}
// /frameworks/base/services/core/java/com/android/server/display/DisplayDeviceRepository.java
//  mDisplayDeviceRepo.onDisplayDeviceEvent(device,
//				DisplayAdapter.DISPLAY_DEVICE_EVENT_ADDED); 
// 這段代碼，會(huì)調(diào)用到下面的函數(shù)中。
private void handleDisplayDeviceAdded(DisplayDevice device) {
	synchronized (mSyncRoot) {
		DisplayDeviceInfo info = device.getDisplayDeviceInfoLocked();
		if (mDisplayDevices.contains(device)) {
			Slog.w(TAG, "Attempted to add already added display device: " + info);
			return;
		}
		Slog.i(TAG, "Display device added: " + info);
		device.mDebugLastLoggedDeviceInfo = info;
		// 需要是將Device（就是上面創(chuàng)建的虛擬屏幕Device）放入到DMS的管理list
		mDisplayDevices.add(device);
		// 通知Device添加，會(huì)調(diào)用到LogicalDisplayMappe的handleDisplayDeviceAddedLocked中。
		sendEventLocked(device, DISPLAY_DEVICE_EVENT_ADDED);
	}
}
// /frameworks/base/services/core/java/com/android/server/display/LogicalDisplayMapper.java
private void handleDisplayDeviceAddedLocked(DisplayDevice device) {
	DisplayDeviceInfo deviceInfo = device.getDisplayDeviceInfoLocked();
	// Internal Displays need to have additional initialization.
	// This initializes a default dynamic display layout for INTERNAL
	// devices, which is used as a fallback in case no static layout definitions
	// exist or cannot be loaded.
	if (deviceInfo.type == Display.TYPE_INTERNAL) {
		initializeInternalDisplayDeviceLocked(device);
	}
	// Create a logical display for the new display device
	LogicalDisplay display = createNewLogicalDisplayLocked(
			device, Layout.assignDisplayIdLocked(false /*isDefault*/));
	// 刷新布局和display配置
	applyLayoutLocked();
	updateLogicalDisplaysLocked();
}