fix: tighten VideoTrackRenderer Widget (#695)

This allows external users to e.g. apply rounded edges. Without this
patch, VideoTrackRenderer will expand to its available space with no way
(known to me..) for parent widgets to know how large the video actually
is.

depends on flutter-webrtc/flutter-webrtc#1754
(and flutter-webrtc/webrtc-interface#30)

Author: holzgeist

lib/src/widgets/video_track_renderer.dart

@@ -65,13 +65,17 @@ class VideoTrackRenderer extends StatefulWidget {
   final rtc.RTCVideoRenderer? cachedRenderer;
   final bool autoDisposeRenderer;
 
+  /// wrap the video view in a Center widget (if [fit] is [VideoViewFit.contain])
+  final bool autoCenter;
+
   const VideoTrackRenderer(
     this.track, {
     this.fit = VideoViewFit.contain,
     this.mirrorMode = VideoViewMirrorMode.auto,
     this.renderMode = VideoRenderMode.texture,
     this.autoDisposeRenderer = true,
     this.cachedRenderer,
+    this.autoCenter = true,
     Key? key,
   }) : super(key: key);
 
@@ -83,6 +87,7 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
   rtc.VideoRenderer? _renderer;
   // for flutter web only.
   bool _rendererReadyForWeb = false;
+  double? _aspectRatio;
   EventsListener<TrackEvent>? _listener;
   // Used to compute visibility information
   late GlobalKey _internalKey;
@@ -121,6 +126,7 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
 
   void disposeRenderer() {
     try {
+      _renderer?.onResize = null;
       _renderer?.srcObject = null;
       _renderer?.dispose();
       _renderer = null;
@@ -167,6 +173,14 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
         // force recompute of mirror mode
         setState(() {});
       });
+    _renderer?.onResize = () {
+      if (mounted) {
+        setState(() {
+          _aspectRatio =
+              (_renderer as rtc.RTCVideoRenderer?)?.videoValue.aspectRatio;
+        });
+      }
+    };
   }
 
   @override
@@ -268,8 +282,52 @@ class _VideoTrackRendererState extends State<VideoTrackRenderer> {
   // FutureBuilder will cause flickering for flutter web. so using
   // different rendering methods for web and native.
   @override
-  Widget build(BuildContext context) =>
-      kIsWeb ? _videoViewForWeb() : _videoViewForNative();
+  Widget build(BuildContext context) {
+    final child = kIsWeb ? _videoViewForWeb() : _videoViewForNative();
+
+    if (widget.fit == VideoViewFit.cover) {
+      return child;
+    }
+
+    final videoView = LayoutBuilder(
+      builder: (BuildContext context, BoxConstraints constraints) {
+        if (!constraints.hasBoundedWidth && !constraints.hasBoundedHeight) {
+          return child;
+        }
+        if (_aspectRatio == null) {
+          return child;
+        }
+
+        bool fixHeight;
+        if (!constraints.hasBoundedWidth) {
+          fixHeight = true;
+        } else if (!constraints.hasBoundedHeight) {
+          fixHeight = false;
+        } else {
+          // both width and height are bound, figure out which to fix based on aspect ratios
+          final constraintsAspectRatio =
+              constraints.maxWidth / constraints.maxHeight;
+          fixHeight = constraintsAspectRatio > _aspectRatio!;
+        }
+        final double width;
+        final double height;
+        if (fixHeight) {
+          height = constraints.maxHeight;
+          width = height * _aspectRatio!;
+        } else {
+          width = constraints.maxWidth;
+          height = width / _aspectRatio!;
+        }
+        return SizedBox(width: width, height: height, child: child);
+      },
+    );
+
+    if (widget.autoCenter) {
+      return Center(child: videoView);
+    } else {
+      return videoView;
+    }
+  }
 
   bool _shouldMirror() {
     // off for screen share