com.unity.uiwidgets/com.unity.uiwidgets/Runtime/rendering/binding.cs

using System;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.gestures;
using Unity.UIWidgets.scheduler;
using Unity.UIWidgets.ui;

namespace Unity.UIWidgets.rendering {
    public class RendererBinding : SchedulerBinding {
        public new static RendererBinding instance {
            get { return (RendererBinding) SchedulerBinding.instance; }
            set { Window.instance._binding = value; }
        }

        protected override void initInstances() {
            base.initInstances();
            instance = this;
            _pipelineOwner = new PipelineOwner(
                onNeedVisualUpdate: ensureVisualUpdate
            );
            Window.instance.onMetricsChanged += handleMetricsChanged;
            Window.instance.onTextScaleFactorChanged += handleTextScaleFactorChanged;
            Window.instance.onPlatformBrightnessChanged += handlePlatformBrightnessChanged;
            initRenderView();
            D.assert(renderView != null);
            addPersistentFrameCallback(_handlePersistentFrameCallback);
            initMouseTracker();
            window.updateSafeArea();
        }
        
        public void initRenderView() {
            D.assert(renderView == null);
            renderView = new RenderView(configuration: createViewConfiguration());
            renderView.prepareInitialFrame();
        }

        public MouseTracker mouseTracker {
            get { return _mouseTracker; }
        }

        MouseTracker _mouseTracker;

        public PipelineOwner pipelineOwner {
            get { return _pipelineOwner; }
        }

        PipelineOwner _pipelineOwner;

        public RenderView renderView {
            get { return (RenderView) _pipelineOwner.rootNode; }
            set { _pipelineOwner.rootNode = value; }
        }

        protected virtual void handleMetricsChanged() {
            D.assert(renderView != null);
            renderView.configuration = createViewConfiguration();
            scheduleForcedFrame();
        }

        protected virtual void handleTextScaleFactorChanged() {
        }

        protected virtual void handlePlatformBrightnessChanged() {
        }

        protected virtual ViewConfiguration createViewConfiguration() {
            var devicePixelRatio = Window.instance.devicePixelRatio;
            return new ViewConfiguration(
                size: Window.instance.physicalSize / devicePixelRatio,
                devicePixelRatio: devicePixelRatio
            );
        }
        
        
        public void initMouseTracker(MouseTracker tracker  = null) {
            _mouseTracker?.dispose();
            _mouseTracker = tracker ?? new MouseTracker(pointerRouter, renderView.hitTestMouseTrackers);
        }

        void _handlePersistentFrameCallback(TimeSpan timeStamp) {
            drawFrame();
            _mouseTracker.schedulePostFrameCheck();
        }

        int _firstFrameDeferredCount = 0;
        bool _firstFrameSent = false;
        bool sendFramesToEngine {
            get {
                return _firstFrameSent || _firstFrameDeferredCount == 0;
            }
        }
        
        void deferFirstFrame() {
            D.assert(_firstFrameDeferredCount >= 0);
            _firstFrameDeferredCount += 1;
        }

        void allowFirstFrame() {
            D.assert(_firstFrameDeferredCount > 0);
            _firstFrameDeferredCount -= 1;
            if (!_firstFrameSent)
                scheduleWarmUpFrame();
        }
        
        void resetFirstFrameSent() {
            _firstFrameSent = false;
        }
        
        readonly protected bool inEditorWindow;

        protected virtual void drawFrame() {
            D.assert(renderView != null);
            pipelineOwner.flushLayout();
            pipelineOwner.flushCompositingBits();
            pipelineOwner.flushPaint();
            if (sendFramesToEngine) {
                renderView.compositeFrame();
                _firstFrameSent = true;
            }
        }

        public override void hitTest(HitTestResult result, Offset position) {
            D.assert(renderView != null);
            renderView.hitTest(result, position: position);
            base.hitTest(result, position);
        }
    }
}