binding.dart

// Copyright 2015 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.

import 'dart:ui' as ui show window;

import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';
import 'package:meta/meta.dart';

import 'box.dart';
import 'debug.dart';
import 'object.dart';
import 'view.dart';
import 'semantics.dart';

export 'package:flutter/gestures.dart' show HitTestResult;

/// The glue between the render tree and the Flutter engine.
abstract class RendererBinding extends BindingBase implements SchedulerBinding, ServicesBinding, HitTestable {
  @override
  void initInstances() {
    super.initInstances();
    _instance = this;
    _pipelineOwner = new PipelineOwner(
      onNeedVisualUpdate: ensureVisualUpdate,
      onSemanticsOwnerCreated: _handleSemanticsOwnerCreated,
      onSemanticsOwnerDisposed: _handleSemanticsOwnerDisposed,
    );
    ui.window
      ..onMetricsChanged = handleMetricsChanged
      ..onSemanticsEnabledChanged = _handleSemanticsEnabledChanged
      ..onSemanticsAction = _handleSemanticsAction;
    initRenderView();
    _handleSemanticsEnabledChanged();
    assert(renderView != null);
    addPersistentFrameCallback(_handlePersistentFrameCallback);
  }

  /// The current [RendererBinding], if one has been created.
  static RendererBinding get instance => _instance;
  static RendererBinding _instance;

  @override
  void initServiceExtensions() {
    super.initServiceExtensions();

    assert(() {
      // this service extension only works in checked mode
      registerBoolServiceExtension(
        name: 'debugPaint',
        getter: () => debugPaintSizeEnabled,
        setter: (bool value) {
          if (debugPaintSizeEnabled == value)
            return;
          debugPaintSizeEnabled = value;
          _forceRepaint();
        }
      );
      return true;
    });

    registerSignalServiceExtension(
      name: 'debugDumpRenderTree',
      callback: debugDumpRenderTree
    );

    assert(() {
      // this service extension only works in checked mode
      registerBoolServiceExtension(
        name: 'repaintRainbow',
        getter: () => debugRepaintRainbowEnabled,
        setter: (bool value) {
          bool repaint = debugRepaintRainbowEnabled && !value;
          debugRepaintRainbowEnabled = value;
          if (repaint)
            _forceRepaint();
        }
      );
      return true;
    });
  }

  /// Creates a [RenderView] object to be the root of the
  /// [RenderObject] rendering tree, and initializes it so that it
  /// will be rendered when the engine is next ready to display a
  /// frame.
  ///
  /// Called automatically when the binding is created.
  void initRenderView() {
    assert(renderView == null);
    renderView = new RenderView(configuration: createViewConfiguration());
    renderView.scheduleInitialFrame();
  }

  /// The render tree's owner, which maintains dirty state for layout,
  /// composite, paint, and accessibility semantics
  PipelineOwner get pipelineOwner => _pipelineOwner;
  PipelineOwner _pipelineOwner;

  /// The render tree that's attached to the output surface.
  RenderView get renderView => _pipelineOwner.rootNode;
  /// Sets the given [RenderView] object (which must not be null), and its tree, to
  /// be the new render tree to display. The previous tree, if any, is detached.
  set renderView(RenderView value) {
    assert(value != null);
    _pipelineOwner.rootNode = value;
  }

  /// Called when the system metrics change.
  ///
  /// See [ui.window.onMetricsChanged].
  void handleMetricsChanged() {
    assert(renderView != null);
    renderView.configuration = createViewConfiguration();
  }

  /// Returns a [ViewConfiguration] configured for the [RenderView] based on the
  /// current environment.
  ///
  /// This is called during construction and also in response to changes to the
  /// system metrics.
  ///
  /// Bindings can override this method to change what size or device pixel
  /// ratio the [RenderView] will use. For example, the testing framework uses
  /// this to force the display into 800x600 when a test is run on the device
  /// using `flutter run`.
  ViewConfiguration createViewConfiguration() {
    final double devicePixelRatio = ui.window.devicePixelRatio;
    return new ViewConfiguration(
      size: ui.window.physicalSize / devicePixelRatio,
      devicePixelRatio: devicePixelRatio
    );
  }

  SemanticsHandle _semanticsHandle;

  void _handleSemanticsEnabledChanged() {
    if (ui.window.semanticsEnabled) {
      _semanticsHandle ??= _pipelineOwner.ensureSemantics();
    } else {
      _semanticsHandle?.dispose();
      _semanticsHandle = null;
    }
  }

  void _handleSemanticsAction(int id, SemanticsAction action) {
    _pipelineOwner.semanticsOwner?.performAction(id, action);
  }

  void _handleSemanticsOwnerCreated() {
    renderView.scheduleInitialSemantics();
  }

  void _handleSemanticsOwnerDisposed() {
    renderView.clearSemantics();
  }

  void _handlePersistentFrameCallback(Duration timeStamp) {
    beginFrame();
  }

  /// Pump the rendering pipeline to generate a frame.
  ///
  /// This method is called by [handleBeginFrame], which itself is called
  /// automatically by the engine when when it is time to lay out and paint a
  /// frame.
  ///
  /// Each frame consists of the following phases:
  ///
  /// 1. The animation phase: The [handleBeginFrame] method, which is registered
  /// with [ui.window.onBeginFrame], invokes all the transient frame callbacks
  /// registered with [scheduleFrameCallback] and [addFrameCallback], in
  /// registration order. This includes all the [Ticker] instances that are
  /// driving [AnimationController] objects, which means all of the active
  /// [Animation] objects tick at this point.
  ///
  /// [handleBeginFrame] then invokes all the persistent frame callbacks, of which
  /// the most notable is this method, [beginFrame], which proceeds as follows:
  ///
  /// 2. The layout phase: All the dirty [RenderObject]s in the system are laid
  /// out (see [RenderObject.performLayout]). See [RenderObject.markNeedsLayout]
  /// for further details on marking an object dirty for layout.
  ///
  /// 3. The compositing bits phase: The compositing bits on any dirty
  /// [RenderObject] objects are updated. See
  /// [RenderObject.markNeedsCompositingBitsUpdate].
  ///
  /// 4. The paint phase: All the dirty [RenderObject]s in the system are
  /// repainted (see [RenderObject.paint]). This generates the [Layer] tree. See
  /// [RenderObject.markNeedsPaint] for further details on marking an object
  /// dirty for paint.
  ///
  /// 5. The compositing phase: The layer tree is turned into a [ui.Scene] and
  /// sent to the GPU.
  ///
  /// 6. The semantics phase: All the dirty [RenderObject]s in the system have
  /// their semantics updated (see [RenderObject.SemanticsAnnotator]). This
  /// generates the [SemanticsNode] tree. See
  /// [RenderObject.markNeedsSemanticsUpdate] for further details on marking an
  /// object dirty for semantics.
  ///
  /// For more details on steps 2-6, see [PipelineOwner].
  ///
  /// 7. The finalization phase: After [beginFrame] returns, [handleBeginFrame]
  /// then invokes post-frame callbacks (registered with [addPostFrameCallback].
  ///
  /// Some bindings (for example, the [WidgetsBinding]) add extra steps to this
  /// list (for example, see [WidgetsBinding.beginFrame]).
  //
  // When editing the above, also update widgets/binding.dart's copy.
  @protected
  void beginFrame() {
    assert(renderView != null);
    pipelineOwner.flushLayout();
    pipelineOwner.flushCompositingBits();
    pipelineOwner.flushPaint();
    renderView.compositeFrame(); // this sends the bits to the GPU
    pipelineOwner.flushSemantics(); // this also sends the semantics to the OS.
  }

  @override
  void reassembleApplication() {
    super.reassembleApplication();
    renderView.reassemble();
    handleBeginFrame(null);
  }

  @override
  void hitTest(HitTestResult result, Point position) {
    assert(renderView != null);
    renderView.hitTest(result, position: position);
    // This super call is safe since it will be bound to a mixed-in declaration.
    super.hitTest(result, position); // ignore: abstract_super_member_reference
  }

  void _forceRepaint() {
    RenderObjectVisitor visitor;
    visitor = (RenderObject child) {
      child.markNeedsPaint();
      child.visitChildren(visitor);
    };
    instance?.renderView?.visitChildren(visitor);
  }
}

/// Prints a textual representation of the entire render tree.
void debugDumpRenderTree() {
  debugPrint(RendererBinding.instance?.renderView?.toStringDeep());
}

/// Prints a textual representation of the entire layer tree.
void debugDumpLayerTree() {
  debugPrint(RendererBinding.instance?.renderView?.layer?.toStringDeep());
}

/// Prints a textual representation of the entire semantics tree.
/// This will only work if there is a semantics client attached.
/// Otherwise, the tree is empty and this will print "null".
void debugDumpSemanticsTree() {
  debugPrint(RendererBinding.instance?.renderView?.debugSemantics?.toStringDeep() ?? 'Semantics not collected.');
}

/// A concrete binding for applications that use the Rendering framework
/// directly. This is the glue that binds the framework to the Flutter engine.
///
/// You would only use this binding if you are writing to the
/// rendering layer directly. If you are writing to a higher-level
/// library, such as the Flutter Widgets library, then you would use
/// that layer's binding.
///
/// See also [BindingBase].
class RenderingFlutterBinding extends BindingBase with SchedulerBinding, GestureBinding, ServicesBinding, RendererBinding {
  /// Creates a binding for the rendering layer.
  ///
  /// The `root` render box is attached directly to the [renderView] and is
  /// given constraints that require it to fill the window.
  RenderingFlutterBinding({ RenderBox root }) {
    assert(renderView != null);
    renderView.child = root;
  }
}