Android使用DisplayManager创建虚拟屏流程及原理解析
目录
- android VirtualDisplay创建流程及原理
- 创建VirtualDisplay
- VirtualDisplay原理
- 如何上屏
Android VirtualDisplay创建流程及原理
Android DisplayManager提供了createVirtualDisplay接口,用于创建虚拟屏。虚拟屏可用于录屏(网上很多资料说这个功能),分屏幕(比如一块很长的屏幕,通过虚拟屏分出不同的区域)等等。
创建VirtualDisplay
DisplayManager中的函数原型如下。后两个Hide的API,只有平台的应用才可以使用。
// 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 fandroidlags) { } 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) { }
补充一点,MediaProjection中也提供了 createVirtualDisplay这个接口,实际上也是通过调用DisplayManager实现的功能。
// 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); // 调用DisplayManager的接口 return dm.createVirt编程客栈ualDisplay(this, virtualDisplayConfig, callback, handler); }
创建VirtualDisplay时,需要传入Surface。**VirtualDisplay上要绘制的内容,实际是通过传入的Surface显示出来的。**比如在主屏(根据物理屏,分配逻辑Display)上创建了一个SurfaceView,通过把这个SurfaceView传给VirtualDisplay。那么VirtualDisplay的 内容,实际上是在主屏的SurfaceView上显示的。下面是一段Android原生的例子。
// 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); // 创建ImageReader,通过它得到一张Surface mReader = ImageReader.newInstance(displayInfo.logicalWidth, displayInfo.logicalHeight, PixelFormat.RGBA_8888, 2); assertNotNull("ImageReader must not be null", mReader); // 创建虚拟屏,传入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(); }
上面的例子中创建虚拟屏,返回Display(实际上是VirtualDislay)对象。有了Display对象,我们就可以将View绑定到这个虚拟的Display上了(绑定网上方法比较多可自行搜索)。关于Surface的创建,有很多种方法,比如通过SurfaceContron+Buffer这种方式也可以。
VituralDisplay创建时,需要提供flag。其值定义如下,可通过 “或”将flag组合。
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;
DisplayManager公开的接口中,有VirtualDisplay.Callback ,提供了其状态的回调。
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() { } }
VirtualDisplay原理
关于VirtualDisplay的实现原理,主要从AndroidFramework角度进行分析。
// /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) { // 走的这里,会调用到DisplayManagerGlobal中。 return mGlobal.createVirtualDisplay(mContext, projection, virtualDisplayConfig, callback, handler); }
DisplayManagerGlobal调用DMS(DisplayManagerService)服务创建虚拟屏,得到DMS返回的DisplayID后,通过DisplayID在Client端创建了VirtualDisplay对象。
// /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); // 从MediaProjection过来的调用,这个地方非空。 IMediaProjection projectionToken = projection != null ? projection.getProjection() : null; int displayId; try { // 告知DMS创建虚拟屏,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; } // 通过DisplayID,取得Display对象信息(也是调用DMS得到的) Display display = getRealDisplay(displayId); if (display == null) { Log.wtf(TAG, "Could not obtain display info for newly created " + "virtual display: " + virthttp://www.devze.comualDisplayConfig.getName()); try { // 创建失败,需要释放 mDm.releaseVirtualDisplay(callbackWrapper); } catch (RemoteException ex) { throw ex.rethrowFromSystemServer(); } return null; } // 创建VirtualDisplay return new VirtualDisplay(this, display, callbackWrapper, virtualDisplayConfig.getSurface()); }
DisplayManagerService(DMS)中创建DisplayDevice并添加到Device列表中管理
// /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) { // 检查uid与包名,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端传过来的surface对象 final Surface surface = virtualDisplayConfig.getSurface(); int flags = virtualDisplayConfig.getFlags(); if (surface != null && surface.isSingleBuffered()) { throw new IllegalArgumentException("Surface can't be single-buffered"); } // 下面开始针对Flag,做一些逻辑判断。 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 { // 调用内部实现 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; } // 为虚拟屏创建Device(告知surfaceflinger创建Display) DisplayDevice device = mVirtualDisplayAdapter.createVirtualDisplayLocked( callback, projection, callingUid, packageName, surface, flags, virtualDisplayConfig); if (device == null) { return -1; } // 发送添加Device通知,这里比较重要 mDisplayDeviceRepo.onDisplayDeviceEvent(device, DisplayAdapter.DISPLAY_DEVICE_EVENT_ADDED); // 检查Display是否创建成功 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; }
接下来DMS开始调用SurfaceFlinger的接口,创建Display。并将Display放入自身的List中管理。
// /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,是判断是否为安全的Display,这个参数会告知SurfaceFlinger boolean secure = (flags & VIRTUAL_DISPLAY_FLAG_SECURE) != 0; IBinder appToken = callback.asBinder(); // 调用SurfaceFligner创建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(); 编程客栈if (uniqueId == null) { uniqueId = baseUniqueId + uniqueIndex; } else { uniqueId = UNIQUE_ID_PREFIX + ownerPackageName + ":" + uniqueId; } // 通过SurfaceFligner返回的displayToken,创建Device对象 VirtualDisplayDevice device = new VirtualDisplayDevice(displayToken, appToken, ownerUid, ownerPackageName, surface, flags, new Callback(callback, mHandler), uniqueId, uniqueIndex, virtualDisplayConfig); // 放到虚拟屏的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); // 这段代码,会调用到下面的函数中。 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; // 需要是将Device(就是上面创建的虚拟屏幕Device)放入到DMS的管理list mDisplayDevices.add(device); // 通知Device添加,会调用到LogicalDisplayMappe的handleDisplayDeviceAddedLocked中。 sendEventLocked(device, DISPLAY_DEVICjsE_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(); }
虚拟屏幕的创建,Client端通过Surface告知的DisplayID,创建VirtualDisplay对象。通过DisplayID,与DMS打交道。DMS服务端,通过SurfaceFlinger创建虚拟屏,拿到SurfaceFligner的DisplayToken,然后通过它创建VirtualDisplayDevice + LogicalDisplay来管理虚拟屏幕。
如何上屏
创建虚拟屏幕的时候,会传入了一张Surface(比如绑定主屏的一张Buffer)。虚拟屏通过这张Surface拿到Surface对应的Buffer,将上屏内容绘制到这个Buffer上,然后提交到画面流水线上(SurfaceFlinger)。通过SurfaceFlinger将这个这个Buffer最终由SurfaceFlinger描画并显示到Surface所在那张Display上(根据VirtualDisplay位置去显示。)
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