Android P刘海屏适配及实现原理

1. Android P 刘海屏的适配

• 介绍：
  Android P 新增了刘海屏的支持，以下内容摘录至Google Android Developer官网：

  Android 9 支持最新的全面屏，其中包含为摄像头和扬声器预留空间的屏幕缺口。 通过 DisplayCutout 类可确定非功能区域的位置和形状，这些区域不应显示内容。 要确定这些屏幕缺口区域是否存在及其位置，请使用 getDisplayCutout() 函数。
  全新的窗口布局属性 layoutInDisplayCutoutMode 让您的应用可以为设备屏幕缺口周围的内容进行布局。 您可以将此属性设为下列值之一：

  LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT
  LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES
  LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER
  可以按以下方法在任何运行 Android 9 的设备或模拟器上模拟屏幕缺口：

  启用开发者选项。
  在 Developer options 屏幕中，向下滚动至 Drawing 部分并选择 Simulate a display with a cutout。
  选择屏幕缺口的大小。
  注：我们建议您通过使用运行 Android 9 的设备或模拟器测试屏幕缺口周围的内容显示。

  官方链接：https://developer.android.com/about/versions/pie/android-9.0#cutout

• 属性以及接口介绍

  • 新增的窗口属性：

    • [->WindowManager.java]

          @LayoutInDisplayCutoutMode
          public int layoutInDisplayCutoutMode = LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT;
      
          public static final int LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT = 0;
      
          /**
           * @deprecated use {@link #LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES}
           * @hide
           */
          @Deprecated
          public static final int LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS = 1;
      
          public static final int LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES = 1;
      
          public static final int LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER = 2;
      

    • 其中每个参数值的含义如下：

      LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT ： 只有当DisplayCutout完全包含在系统栏中时，才允许窗口延伸到DisplayCutout区域。 否则，窗口布局不与DisplayCutout区域重叠。 （有状态栏时，不下压；没有状态栏全屏显示时，下压）；

      LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER ： 该窗口决不允许与DisplayCutout区域重叠。 （强制下压）；

      LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES ： 该窗口始终允许延伸到屏幕短边上的DisplayCutout区域。 （不处理）；

      LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS ： 不再使用，与LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES；

  • 刘海参数

    • 获取DisplayCutout对象：

      方法一：
      private final DisplayInfo mInfo = new DisplayInfo();
      getDisplay().getDisplayInfo(mInfo);
      mInfo.displayCutout;
      
      方法二：
      final View decorView = getWindow().getDecorView();
      DisplayCutout displayCutout = decorView.getRootWindowInsets().getDisplayCutout();
      

    • 获取缺口位置和安全区域位置：

      getBoundingRects ()：返回Rects的列表，每个Rects都是显示屏上非功能区域的边界矩形。
      getSafeInsetXXX ()：返回安全区域的距离屏幕的距离（XXX表示Left，Right等）
      

    需要注意的是，其中getBoundingRects() 返回缺口位置的一个列表，表明可能存在多个缺口区域（一般只有一个），其中列表中顺序分别为：上缺口参数、左缺口参数、下右缺口参数

• 应用适配

  • 全屏窗口：

    • 若想自身内容不被遮挡，可配置窗口属性LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER进行强制下压，或不做任何配置直接使用默认值；然后获取刘海的参数应用内部适配

    WindowManager.LayoutParams lp = getWindow().getAttributes();
    lp.layoutInDisplayCutoutMode = WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER;
    

    • 若想自身内容显示在刘海区域下，可配置窗口属性LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES，系统将不做任何处理；

    WindowManager.LayoutParams lp = getWindow().getAttributes();
    lp.layoutInDisplayCutoutMode = WindowManager.LayoutParams.LAYOUT_IN_DISPLAY_CUTOUT_MODE_SHORT_EDGES;
    

  • 非全屏窗口（状态栏显示）：不用适配

2. 实现的原理

• 相关类

  • 设置：
    EmulateDisplayCutoutPreferenceController.java
    OverlayManagerWrapper.java
  • Framework:
    OverlayManagerService.java
    OverlayManagerServiceImpl.java
    DisplayManagerService.java
    LocalDisplayAdapter.java
    DisplayAdapter.java
    DisplayCutout.java
    PhoneWindowManager.java
    WindowManager.java
  • Overlay的资源应用：
    DisplayCuoutEmulationTallOverlay;
    DisplayCuoutEmulationWideOverlay;
    DisplayCuoutEmulationCornerOverlay;
    DisplayCuoutEmulationDoubleOverlay;
    DisplayCuoutEmulationNarrowOverlay;
  • SystemUI：
    ScreenDecorations.java

• 显示刘海缺口窗口

  • 设置–开发者选项–模拟“刘海屏”

    • 选择不同的刘海屏选项后会回调EmulateDisplayCutoutPreferenceController.setEmulationOverlay(); 然后执行mOverlayManager中的方法

      [->EmulateDisplayCutoutPreferenceController.java]

       private boolean setEmulationOverlay(String packageName) {
          ....
          final boolean result;
          if (TextUtils.isEmpty(packageName)) {
              result = mOverlayManager.setEnabled(currentPackageName, false, USER_SYSTEM);
          } else {
              result = mOverlayManager.setEnabledExclusiveInCategory(packageName, USER_SYSTEM);
          }
          .....
      }
      

    • 最终会执行OverlayManagerServiceImpl.setEnabledExclusive()，通过enalbe和diable 不同资源的Overlay应用，实现动态资源替换（Overlay）:
      [->OverlayManagerServiceImpl.java]

      boolean setEnabledExclusive(@NonNull final String packageName, boolean withinCategory,
              final int userId) {
              ....
              // Disable the overlay.
                  modified |= mSettings.setEnabled(disabledOverlayPackageName, userId, false);
                  modified |= updateState(targetPackageName, disabledOverlayPackageName, userId, 0);
              ....
              // Enable the selected overlay.
              modified |= mSettings.setEnabled(packageName, userId, true);
              modified |= updateState(targetPackageName, packageName, userId, 0);    
              .....
              if (modified) {
                  mListener.onOverlaysChanged(targetPackageName, userId);
              }
              return true;
              ......
      }
      

    • 通过mListener.onOverlaysChanged()通知Overlay资源变换，触发DisplayManagerService.LocalService.onOverlayChanged()的回调，然后更新DisplayCutout的mBounds和mSafeInsets 数据；

  • 更新DisplayCutout数据

    • 如上所述，DisplayManagerService.LocalService.onOverlayChanged()的回调 会触发LocalDisplayAdapter.LocalDisplayDevice.requestDisplayModesLocked()的执行，然后updateDeviceInfoLocked()–>sendDisplayDeviceEventLocked()：

      [->LocalDisplayAdapter.java]

      ....
      @Override
          public void requestDisplayModesLocked(int colorMode, int modeId) {
              if (requestModeLocked(modeId) ||
                      requestColorModeLocked(colorMode)) {
                  updateDeviceInfoLocked();
              }
          }
      ....    
      
      sendDisplayDeviceEventLocked(this, DISPLAY_DEVICE_EVENT_CHANGED); 
      
      .....
      
      /**
       * Sends a display device event to the display adapter listener asynchronously.
       */
      protected final void sendDisplayDeviceEventLocked(
              final DisplayDevice device, final int event) {
          mHandler.post(new Runnable() {
              @Override
              public void run() {
                  mListener.onDisplayDeviceEvent(device, event);
              }
          });
      }
      

    • 其中sendDisplayDeviceEventLocked(), 又会回调DisplayManagerService.DisplayAdapterListener.onDisplayDeviceEvent, 其中handleDisplayDeviceChanged(device)–>device.getDisplayDeviceInfoLocked():

      [->DisplayManagerService.java]

          private final class DisplayAdapterListener implements DisplayAdapter.Listener {
              @Override
              public void onDisplayDeviceEvent(DisplayDevice device, int event) {
                  switch (event) {
                      case DisplayAdapter.DISPLAY_DEVICE_EVENT_ADDED:
                          handleDisplayDeviceAdded(device);
                          break;
      
                      case DisplayAdapter.DISPLAY_DEVICE_EVENT_CHANGED:
                          handleDisplayDeviceChanged(device);
                          break;
      
                      case DisplayAdapter.DISPLAY_DEVICE_EVENT_REMOVED:
                          handleDisplayDeviceRemoved(device);
                          break;
                  }
              }
      
              ......
          }
      
          ......
          private void handleDisplayDeviceChanged(DisplayDevice device) {
              synchronized (mSyncRoot) {
                  DisplayDeviceInfo info = device.getDisplayDeviceInfoLocked();
                  if (!mDisplayDevices.contains(device)) {
                      Slog.w(TAG, "Attempted to change non-existent display device: " + info);
                      return;
                  }
      
                  int diff = device.mDebugLastLoggedDeviceInfo.diff(info);
                  if (diff == DisplayDeviceInfo.DIFF_STATE) {
                      Slog.i(TAG, "Display device changed state: \"" + info.name
                              + "\", " + Display.stateToString(info.state));
                  } else if (diff != 0) {
                      Slog.i(TAG, "Display device changed: " + info);
                  }
                  if ((diff & DisplayDeviceInfo.DIFF_COLOR_MODE) != 0) {
                      try {
                          mPersistentDataStore.setColorMode(device, info.colorMode);
                      } finally {
                          mPersistentDataStore.saveIfNeeded();
                      }
                  }
                  device.mDebugLastLoggedDeviceInfo = info;
      
                  device.applyPendingDisplayDeviceInfoChangesLocked();
                  if (updateLogicalDisplaysLocked()) {
                      scheduleTraversalLocked(false);
                  }
              }
          }
      
      

    • 最终又回到LocalDisplayAdapter.getDisplayDeviceInfoLocked(),
      DisplayCutout.fromResources(res, mInfo.width, mInfo.height)方法会被调用；

      public DisplayDeviceInfo getDisplayDeviceInfoLocked() {
          ....
          mInfo.displayCutout = DisplayCutout.fromResources(res, mInfo.width,
                      mInfo.height);
          .....            
      }
      
      

  • 确定刘海的缺口形状和大小

    • 刘海缺口的形状通过path来确定，而path数据则有上面各个overlay app中存储,R.string.config_mainBuiltInDisplayCutout

      [-> DisplayCutout.java]

      /**
       * Creates the bounding path according to @android:string/config_mainBuiltInDisplayCutout.
       *
       * @hide
       */
      public static DisplayCutout fromResources(Resources res, int displayWidth, int displayHeight) {
          return fromSpec(res.getString(R.string.config_mainBuiltInDisplayCutout),
                  displayWidth, displayHeight, DENSITY_DEVICE_STABLE / (float) DENSITY_DEFAULT);
      }
      
      private static Pair pathAndDisplayCutoutFromSpec(String spec,
              int displayWidth, int displayHeight, float density) {
         
          .....
          
          final Pair result = new Pair<>(p, fromBounds(p));
         
          ......
          return result;
      }
      ....
      /**
       * Creates an instance from a bounding {@link Path}.
       *
       * @hide
       */
      public static DisplayCutout fromBounds(Path path) {
          RectF clipRect = new RectF();
          path.computeBounds(clipRect, false /* unused */);
          Region clipRegion = Region.obtain();
          clipRegion.set((int) clipRect.left, (int) clipRect.top,
                  (int) clipRect.right, (int) clipRect.bottom);
      
          Region bounds = new Region();
          bounds.setPath(path, clipRegion);
          clipRegion.recycle();
          return new DisplayCutout(ZERO_RECT, bounds, false /* copyArguments */);
      }
      

  • 显示刘海缺口

    • 显示刘海缺口在SystemUI中的ScreenDecorations，通过注册监听Display的变化来触发更新, 最终显示到屏幕上；

      [->ScreenDecorations.java]

      @Override
      protected void onAttachedToWindow() {
          super.onAttachedToWindow();
          mContext.getSystemService(DisplayManager.class).registerDisplayListener(this,
                  getHandler());
          update();
      }
      
      @Override
      protected void onDetachedFromWindow() {
          super.onDetachedFromWindow();
          mContext.getSystemService(DisplayManager.class).unregisterDisplayListener(this);
      }
      
      .....
      @Override
      public void onDisplayChanged(int displayId) {
          if (displayId == getDisplay().getDisplayId()) {
              update();
          }
      }
      .....
      
      private void update() {
          requestLayout();
          getDisplay().getDisplayInfo(mInfo);
          mBounds.setEmpty();
          mBoundingRect.setEmpty();
          mBoundingPath.reset();
          int newVisible;
          if (shouldDrawCutout(getContext()) && hasCutout()) {
              mBounds.set(mInfo.displayCutout.getBounds());
              localBounds(mBoundingRect);
              updateBoundingPath();
              invalidate();
              newVisible = VISIBLE;
          } else {
              newVisible = GONE;
          }
          if (newVisible != getVisibility()) {
              setVisibility(newVisible);
              mVisibilityChangedListener.run();
          }
      }
      .....
      

• 刘海下压

  • PhoneWindowManager 利用DisplayCutout数据，根据窗口的类型和属性等条件来判断是否下压窗口

    [->PhoneWindowManager.java]

    /** {@inheritDoc} */
    @Override
    public void layoutWindowLw(WindowState win, WindowState attached, DisplayFrames displayFrames) {
        ....
        
        // Ensure that windows with a DEFAULT or NEVER display cutout mode are laid out in
        // the cutout safe zone.
        if (cutoutMode != LAYOUT_IN_DISPLAY_CUTOUT_MODE_ALWAYS) {
            final Rect displayCutoutSafeExceptMaybeBars = mTmpDisplayCutoutSafeExceptMaybeBarsRect;
            displayCutoutSafeExceptMaybeBars.set(displayFrames.mDisplayCutoutSafe);
            if (layoutInScreen && layoutInsetDecor && !requestedFullscreen
                    && cutoutMode == LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT) {
                // At the top we have the status bar, so apps that are
                // LAYOUT_IN_SCREEN | LAYOUT_INSET_DECOR but not FULLSCREEN
                // already expect that there's an inset there and we don't need to exclude
                // the window from that area.
                displayCutoutSafeExceptMaybeBars.top = Integer.MIN_VALUE;
            }
            if (layoutInScreen && layoutInsetDecor && !requestedHideNavigation
                    && cutoutMode == LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT) {
                // Same for the navigation bar.
                switch (mNavigationBarPosition) {
                    case NAV_BAR_BOTTOM:
                        displayCutoutSafeExceptMaybeBars.bottom = Integer.MAX_VALUE;
                        break;
                    case NAV_BAR_RIGHT:
                        displayCutoutSafeExceptMaybeBars.right = Integer.MAX_VALUE;
                        break;
                    case NAV_BAR_LEFT:
                        displayCutoutSafeExceptMaybeBars.left = Integer.MIN_VALUE;
                        break;
                }
            }
            if (type == TYPE_INPUT_METHOD && mNavigationBarPosition == NAV_BAR_BOTTOM) {
                // The IME can always extend under the bottom cutout if the navbar is there.
                displayCutoutSafeExceptMaybeBars.bottom = Integer.MAX_VALUE;
            }
            // Windows that are attached to a parent and laid out in said parent already avoid
            // the cutout according to that parent and don't need to be further constrained.
            // Floating IN_SCREEN windows get what they ask for and lay out in the full screen.
            // They will later be cropped or shifted using the displayFrame in WindowState,
            // which prevents overlap with the DisplayCutout.
            if (!attachedInParent && !floatingInScreenWindow) {
                mTmpRect.set(pf);
                pf.intersectUnchecked(displayCutoutSafeExceptMaybeBars);
                parentFrameWasClippedByDisplayCutout |= !mTmpRect.equals(pf);
            }
            // Make sure that NO_LIMITS windows clipped to the display don't extend under the
            // cutout.
            df.intersectUnchecked(displayCutoutSafeExceptMaybeBars);
        }
        
        ......
    }
    

3. 小结

由开发者选项的模拟刘海作为切入口，分析Android P刘海屏的实现原理，其中涉及到3个进程内容，分别是Settings进程、SystemUI进程以及最重要的System_server进程，三个进程各司其职