Implement PlatformViewsController. (#5722)

Each platform view created (by a plugin supplied factory) is attached to
a virtual display.
The virtual displays are controlled by VirtualDisplayController objects.
The PlatformViewsController maintains a mapping from a platform view's
id to its VirtualDisplayController, which allows it to operate on the
virtual display for a given platform view ID when asked so over the
method channel.

This is using API level 20 APIs, on lower API levels all platform views
method channel calls are noops.
We can make this work on API 19 with some refactoring to the
TextureRegistry (allow the engine Java code to recycle a texture entry
id).

This CL also adds a platform view id parameter to the
PlatformViewFactory#create() method. This allows plugins to route
platform channel messages to specific instances of a platform view.

TBD in future CLs:
  * Forward touch events to the platform views.
  * Support accessibility for platform views.

flutter/flutter#19030

shell/platform/android/BUILD.gn

@@ -129,6 +129,8 @@ java_library("flutter_shell_java") {
     "io/flutter/plugin/platform/PlatformViewRegistry.java",
     "io/flutter/plugin/platform/PlatformViewRegistryImpl.java",
     "io/flutter/plugin/platform/PlatformViewsController.java",
+    "io/flutter/plugin/platform/SingleViewPresentation.java",
+    "io/flutter/plugin/platform/VirtualDisplayController.java",
     "io/flutter/util/PathUtils.java",
     "io/flutter/util/Preconditions.java",
     "io/flutter/view/AccessibilityBridge.java",

shell/platform/android/io/flutter/plugin/platform/PlatformView.java

@@ -14,4 +14,14 @@ public interface PlatformView {
      * Returns the Android view to be embedded in the Flutter hierarchy.
      */
     View getView();
+
+    /**
+     * Dispose this platform view.
+     *
+     * <p>The {@link PlatformView} object is unusable after this method is called.
+     *
+     * <p>Plugins implementing {@link PlatformView} must clear all references to the View object and the PlatformView
+     * after this method is called. Failing to do so will result in a memory leak.
+     */
+    void dispose();
 }

shell/platform/android/io/flutter/plugin/platform/PlatformViewFactory.java

@@ -7,5 +7,11 @@ package io.flutter.plugin.platform;
 import android.content.Context;
 
 public interface PlatformViewFactory {
-    PlatformView create(Context context);
+    /**
+     * Creates a new Android view to be embedded in the Flutter hierarchy.
+     *
+     * @param context the context to be used when creating the view, this is different than FlutterView's context.
+     * @param viewId unique identifier for the created instance, this value is known on the Dart side.
+     */
+    PlatformView create(Context context, int viewId);
 }

shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java

@@ -4,11 +4,15 @@
 
 package io.flutter.plugin.platform;
 
+import android.annotation.TargetApi;
+import android.content.Context;
+import android.os.Build;
 import android.util.Log;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.StandardMethodCodec;
 import io.flutter.view.FlutterView;
+import io.flutter.view.TextureRegistry;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -20,14 +24,22 @@ import java.util.Map;
  * A platform views controller can be attached to at most one Flutter view.
  */
 public class PlatformViewsController implements MethodChannel.MethodCallHandler {
+    private static final String TAG = "PlatformViewsController";
+
     private static final String CHANNEL_NAME = "flutter/platform_views";
 
+    // API level 20 is required for VirtualDisplay#setSurface which we use when resizing a platform view.
+    private static final int MINIMAL_SDK = Build.VERSION_CODES.KITKAT_WATCH;
+
     private final PlatformViewRegistryImpl mRegistry;
 
     private FlutterView mFlutterView;
 
+    private final HashMap<Integer, VirtualDisplayController> vdControllers;
+
     public PlatformViewsController() {
         mRegistry = new PlatformViewRegistryImpl();
+        vdControllers = new HashMap<>();
     }
 
     public void attachFlutterView(FlutterView view) {
@@ -51,48 +63,129 @@ public class PlatformViewsController implements MethodChannel.MethodCallHandler
     }
 
     public void onFlutterViewDestroyed() {
-        // TODO(amirh): tear down all vd resources.
+        for (VirtualDisplayController controller : vdControllers.values()) {
+            controller.dispose();
+        }
+        vdControllers.clear();
     }
 
     @Override
-    public void onMethodCall(MethodCall call, MethodChannel.Result result) {
+    public void onMethodCall(final MethodCall call, final MethodChannel.Result result) {
+        if (Build.VERSION.SDK_INT < MINIMAL_SDK) {
+            Log.e(TAG, "Trying to use platform views with API " + Build.VERSION.SDK_INT
+                    + ", required API level is: " + MINIMAL_SDK);
+            return;
+        }
         switch (call.method) {
             case "create":
-                createPlatformView(call);
-                break;
+                createPlatformView(call, result);
+                return;
             case "dispose":
-                disposePlatformView(call);
-                break;
+                disposePlatformView(call, result);
+                return;
             case "resize":
-                resizePlatformView(call);
-                break;
+                resizePlatformView(call, result);
+                return;
         }
-        result.success(null);
+        result.notImplemented();
     }
 
-    private void createPlatformView(MethodCall call) {
+    @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1)
+    private void createPlatformView(MethodCall call, MethodChannel.Result result) {
         Map<String, Object> args = call.arguments();
         int id = (int) args.get("id");
         String viewType = (String) args.get("viewType");
-        double width = (double) args.get("width");
-        double height = (double) args.get("height");
+        double logicalWidth = (double) args.get("width");
+        double logicalHeight = (double) args.get("height");
+
+        if (vdControllers.containsKey(id)) {
+            result.error(
+                    "error",
+                    "Trying to create an already created platform view, view id: " + id,
+                    null
+            );
+            return;
+        }
+
+        PlatformViewFactory viewFactory = mRegistry.getFactory(viewType);
+        if (viewFactory == null) {
+            result.error(
+                    "error",
+                    "Trying to create a platform view of unregistered type: " + viewType,
+                    null
+            );
+            return;
+        }
+
+        TextureRegistry.SurfaceTextureEntry textureEntry = mFlutterView.createSurfaceTexture();
+        VirtualDisplayController vdController = VirtualDisplayController.create(
+                mFlutterView.getContext(),
+                viewFactory,
+                textureEntry.surfaceTexture(),
+                toPhysicalPixels(logicalWidth),
+                toPhysicalPixels(logicalHeight),
+                id
+        );
 
-        // TODO(amirh): implement this.
+        if (vdController == null) {
+            result.error(
+                    "error",
+                    "Failed creating virtual display for a " + viewType + " with id: " + id,
+                    null
+            );
+            return;
+        }
+
+        vdControllers.put(id, vdController);
+
+        // TODO(amirh): copy accessibility nodes to the FlutterView's accessibility tree.
+
+        result.success(textureEntry.id());
     }
 
-    private void disposePlatformView(MethodCall call) {
-        int id = (int) call.arguments();
+    private void disposePlatformView(MethodCall call, MethodChannel.Result result) {
+        int id = call.arguments();
 
-        // TODO(amirh): implement this.
+        VirtualDisplayController vdController = vdControllers.get(id);
+        if (vdController == null) {
+            result.error(
+                    "error",
+                    "Trying to dispose a platform view with unknown id: " + id,
+                    null
+            );
+            return;
         }
 
-    private void resizePlatformView(MethodCall call) {
+        vdController.dispose();
+        vdControllers.remove(id);
+        result.success(null);
+    }
+
+    private void resizePlatformView(MethodCall call, MethodChannel.Result result) {
         Map<String, Object> args = call.arguments();
         int id = (int) args.get("id");
         double width = (double) args.get("width");
         double height = (double) args.get("height");
 
-        // TODO(amirh): implement this.
+        VirtualDisplayController vdController = vdControllers.get(id);
+        if (vdController == null) {
+            result.error(
+                    "error",
+                    "Trying to resize a platform view with unknown id: " + id,
+                    null
+            );
+            return;
+        }
+        vdController.resize(
+                toPhysicalPixels(width),
+                toPhysicalPixels(height)
+        );
+        result.success(null);
+    }
+
+    private int toPhysicalPixels(double logicalPixels) {
+        float density = mFlutterView.getContext().getResources().getDisplayMetrics().density;
+        return (int) Math.round(logicalPixels * density);
     }
 
 }

shell/platform/android/io/flutter/plugin/platform/SingleViewPresentation.java

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugin.platform;
+
+import android.annotation.TargetApi;
+import android.app.Presentation;
+import android.content.Context;
+import android.os.Build;
+import android.os.Bundle;
+import android.view.Display;
+import android.widget.FrameLayout;
+
+@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
+class SingleViewPresentation extends Presentation {
+    private final PlatformViewFactory mViewFactory;
+
+    private PlatformView mView;
+    private int mViewId;
+
+    // As the root view of a display cannot be detached, we use this mContainer
+    // as the root, and attach mView to it. This allows us to detach mView.
+    private FrameLayout mContainer;
+
+    /**
+     * Creates a presentation that will use the view factory to create a new
+     * platform view in the presentation's onCreate, and attach it.
+     */
+    public SingleViewPresentation(Context outerContext, Display display, PlatformViewFactory viewFactory, int viewId) {
+        super(outerContext, display);
+        mViewFactory = viewFactory;
+        mViewId = viewId;
+    }
+
+    /**
+     * Creates a presentation that will attach an already existing view as
+     * its root view.
+     *
+     * <p>The display's density must match the density of the context used
+     * when the view was created.
+     */
+    public SingleViewPresentation(Context outerContext, Display display, PlatformView view) {
+        super(outerContext, display);
+        mViewFactory = null;
+        mView = view;
+    }
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        if (mView == null) {
+            mView = mViewFactory.create(getContext(), mViewId);
+        }
+        mContainer = new FrameLayout(getContext());
+        mContainer.addView(mView.getView());
+        setContentView(mContainer);
+    }
+
+    public PlatformView detachView() {
+        mContainer.removeView(mView.getView());
+        return mView;
+    }
+}

shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugin.platform;
+
+import android.annotation.TargetApi;
+import android.content.Context;
+import android.graphics.SurfaceTexture;
+import android.hardware.display.DisplayManager;
+import android.hardware.display.VirtualDisplay;
+import android.os.Build;
+import android.view.Surface;
+import android.view.View;
+
+@TargetApi(Build.VERSION_CODES.KITKAT_WATCH)
+class VirtualDisplayController {
+
+    public static VirtualDisplayController create(
+            Context context,
+            PlatformViewFactory viewFactory,
+            SurfaceTexture surfaceTexture,
+            int width,
+            int height,
+            int viewId
+    ) {
+        surfaceTexture.setDefaultBufferSize(width, height);
+        Surface surface = new Surface(surfaceTexture);
+        DisplayManager displayManager = (DisplayManager) context.getSystemService(Context.DISPLAY_SERVICE);
+
+        int densityDpi = context.getResources().getDisplayMetrics().densityDpi;
+        VirtualDisplay virtualDisplay = displayManager.createVirtualDisplay(
+                "flutter-vd",
+                width,
+                height,
+                densityDpi,
+                surface,
+                0
+        );
+
+        if (virtualDisplay == null) {
+            return null;
+        }
+
+        return new VirtualDisplayController(context, virtualDisplay, viewFactory, surface, surfaceTexture, viewId);
+    }
+
+    private final Context mContext;
+    private final int mDensityDpi;
+    private final SurfaceTexture mSurfaceTexture;
+    private VirtualDisplay mVirtualDisplay;
+    private SingleViewPresentation mPresentation;
+    private Surface mSurface;
+
+
+    private VirtualDisplayController(
+            Context context,
+            VirtualDisplay virtualDisplay,
+            PlatformViewFactory viewFactory,
+            Surface surface,
+            SurfaceTexture surfaceTexture,
+            int viewId
+    ) {
+        mSurfaceTexture = surfaceTexture;
+        mSurface = surface;
+        mContext = context;
+        mVirtualDisplay = virtualDisplay;
+        mDensityDpi = context.getResources().getDisplayMetrics().densityDpi;
+        mPresentation = new SingleViewPresentation(context, mVirtualDisplay.getDisplay(), viewFactory, viewId);
+        mPresentation.show();
+    }
+
+    public void resize(int width, int height) {
+        PlatformView view = mPresentation.detachView();
+        mPresentation.hide();
+        // We detach the surface to prevent it being destroyed when releasing the vd.
+        //
+        // setSurface is only available starting API 20. We could support API 19 by re-creating a new
+        // SurfaceTexture here. This will require refactoring the TextureRegistry to allow recycling texture
+        // entry IDs.
+        mVirtualDisplay.setSurface(null);
+        mVirtualDisplay.release();
+
+        mSurfaceTexture.setDefaultBufferSize(width, height);
+        DisplayManager displayManager = (DisplayManager) mContext.getSystemService(Context.DISPLAY_SERVICE);
+        mVirtualDisplay = displayManager.createVirtualDisplay(
+                "flutter-vd",
+                width,
+                height,
+                mDensityDpi,
+                mSurface,
+                0
+        );
+        mPresentation = new SingleViewPresentation(mContext, mVirtualDisplay.getDisplay(), view);
+        mPresentation.show();
+    }
+
+    public void dispose() {
+        mPresentation.detachView().dispose();
+        mVirtualDisplay.release();
+    }
+}

travis/licenses_golden/licenses_flutter

@@ -501,6 +501,8 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/Platfor
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistry.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistryImpl.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/SingleViewPresentation.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/plugin/platform/VirtualDisplayController.java
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterCallbackCache.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterPluginAppLifeCycleDelegate.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterCallbackCache.mm