[framework] simplify raster widget, rename, combine painters #109485

jonahwilliams · 2022-08-13T04:06:22Z

Greatly simplifies the raster widget, renaming to snapshot widget.

While working to use the raster widget in more animated examples, I found that generally it was still difficult to switch between the custom painter like behavior and regular widgets - especially if the child may have a platform view, but also because we may need to pause the animation on a rotation or partial opacity. If an animation is paused, then we should of course render the regular widget children so they are interactable. Thus we need to add a painter and fallback for almost every usage, which doesn't feel like its working well enough.

While using regular widgets instead of the painter still turned out to be a performance regression, we can atleast simplify the delegates and rendering modes so that it is more obvious what a "normal" usage of the snapshot widget is

…to snapshot_widget

flutter-dashboard · 2022-08-15T17:46:13Z

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Changes reported for pull request #109485 at sha 5bddb9a

goderbauer

I like how this change simplifies usage of the widget.

goderbauer · 2022-08-15T23:23:59Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+
+/// Controls how the [SnapshotWidget] paints its child via the [SnapshotWidgetController].
+enum SnapshotMode {
+  /// the child is snapshotted, but only if all descendants can be snapshotted.


goderbauer · 2022-08-15T23:24:05Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+  /// snapshot will not be used and the child will be rendered as normal.
+  permissive,
+
+  /// the child is snapshotted, but only if all descendants can be snapshotted.


goderbauer · 2022-08-15T23:24:53Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+  /// the child is snapshotted, but only if all descendants can be snapshotted.
+  ///
+  /// If there is a platform view in the children of a raster widget, the
+  /// snapshot will not be used and the child will be rendered as normal.


normal as an SnapshotMode.normal (which seems to indicate that this would throw) or is this a different normal?

hmm, no - not sure how else to phrase this - the normal way as in ... super.paint

instead of calling it normal maybe say things will be rendered like they would if no SnapshotWidget were to be used?

but we still use the painter

goderbauer · 2022-08-15T23:28:19Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+  }
+
+  /// Whether a snapshot of this child widget is painted in its place.
+  bool get enabled => _enabled;


When first reading through this I got confused what the "enabled" state is. Maybe rename this to allowSnapshotting to avoid confusion? It implies that if that to true, snapshotting may happen if other parameters line up, but it is not guaranteed.

goderbauer · 2022-08-15T23:29:07Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+/// be expensive or that cannot rely on raster caching. For example, scale and
+/// skew animations are often expensive to perform on complex children, as are
+/// blurs. For a short animation, a widget that contains these expensive effects
+/// can be replaced with a snapshot of it self and manipulated instead.


it self -> itself? (I think)

goderbauer · 2022-08-15T23:45:13Z

packages/flutter/test/widgets/snapshot_widget_test.dart

+
+    // Now invoke clear and the raster is re-generated.
+    controller.clear();
+    await tester.pumpAndSettle();


await tester.pump() should do here? This all is expected to happen in the next frame, no?

goderbauer · 2022-08-15T23:46:07Z

packages/flutter/test/widgets/snapshot_widget_test.dart

+}
+
+class RenderTestPlatformView extends RenderProxyBox {
+


nit: remove blank line.

goderbauer · 2022-08-15T23:48:40Z

packages/flutter/lib/src/material/page_transitions_theme.dart

@@ -392,10 +401,8 @@ class _ZoomExitTransition extends StatefulWidget {
 }

 class _ZoomExitTransitionState extends State<_ZoomExitTransition> with _ZoomTransitionBase {
-  late _ZoomExitTransitionDelegate delegate;
-
-  // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689


Does this TODO still apply?

Same as above

goderbauer · 2022-08-15T23:49:12Z

packages/flutter/lib/src/material/page_transitions_theme.dart

@@ -285,10 +283,8 @@ class _ZoomEnterTransition extends StatefulWidget {
 }

 class _ZoomEnterTransitionState extends State<_ZoomEnterTransition> with _ZoomTransitionBase {
-  // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689


Does this TODO still apply?

From benchmarking, we don't want to use snapshotting on the web due to the single frame

Maybe add that context as a comment here to explain why we don't want this on the web?

goderbauer · 2022-08-15T23:50:53Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+///   defaults to [SnapshotMode.normal] which will throw an exception if a
+///   platform view is encountered.
+///
+/// * This widget is not supported on the HTML backend of Flutter for the web.


document what "not supported" means. Is this widget always a no-op on the web? Are you never allowed to instantiate this on the web? What happens if you do?

I arrived at this question because the ZoomTransition appears to unconditionally be using this widget. So, some modes of this widget must be supported on the web??

Not sure the best way to phrase this, I tried some updates

goderbauer · 2022-08-15T23:57:46Z

Do you have benchmark numbers to check whether this approach does anything to the performance of the page transition? Or does this have the same performance characteristics?

…to snapshot_widget

jonahwilliams · 2022-08-16T18:32:34Z

I backed out the widget changes, I couldn't claw back enough performance to justify removing the delegate

flutter-dashboard · 2022-08-17T04:09:16Z

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jonahwilliams · 2022-08-17T19:05:07Z

@goderbauer I added some questions on documentation updates

goderbauer · 2022-08-18T17:53:28Z

packages/flutter/lib/src/material/page_transitions_theme.dart

@@ -285,10 +283,8 @@ class _ZoomEnterTransition extends StatefulWidget {
 }

 class _ZoomEnterTransitionState extends State<_ZoomEnterTransition> with _ZoomTransitionBase {
-  // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689


Maybe add that context as a comment here to explain why we don't want this on the web?

goderbauer · 2022-08-18T18:11:18Z

packages/flutter/test/widgets/snapshot_widget_test.dart

+        ),
+      ),
+    ));
+    await tester.pump();


Do you need this pump? The snapshot widget should be doing all its magic in one frame, no?

(same for the extra pumps below)

goderbauer · 2022-08-18T18:14:37Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+  /// the child is snapshotted, but only if all descendants can be snapshotted.
+  ///
+  /// If there is a platform view in the children of a raster widget, the
+  /// snapshot will not be used and the child will be rendered as normal.


instead of calling it normal maybe say things will be rendered like they would if no SnapshotWidget were to be used?

goderbauer · 2022-08-18T18:15:17Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+enum SnapshotMode {
+  /// The child is snapshotted, but only if all descendants can be snapshotted.
+  ///
+  /// If there is a platform view in the children of a raster widget, the


nit: its not called raster widget anymore..

goderbauer · 2022-08-18T18:18:10Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+  }
+
+  @override
+  // ignore: library_private_types_in_public_api


Elsewhere, we just declare the parameter as RenderObject and cast inside the method to the private type. Any reason not to do that here?

goderbauer · 2022-08-18T18:20:30Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+      return;
+    }
+    _devicePixelRatio = value;
+    markNeedsPaint();


Do we need to throw away the rastered image to force re-rasterization with the new paint?

Also tiny optimization: do we need a paint if _childRaster is currently null and not used?

goderbauer · 2022-08-18T18:20:40Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+    markNeedsPaint();
+  }
+
+ /// The painter used to paint the child snapshot or child widgets.


nit: indentation

goderbauer · 2022-08-18T18:24:20Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+      if (mode == SnapshotMode.normal) {
+        throw FlutterError('SnapshotWidget used with a child that contains a PlatformView.');
+      }
+      _disableSnapshotAttempt = true;


There doesn't appear to be a path that ever resets this to false? Is that expected? There are no conditions where we can try snapshotting again?

Perhaps on detach we can reset the value?

and also on reset

or just on notification from the controller

goderbauer · 2022-08-18T18:26:06Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+  /// The [offset] and [size] are the location and dimensions of the render object.
+  void paint(PaintingContext context, Offset offset, Size size, PaintingContextCallback painter);
+
+  /// Called whenever a new instance of the raster widget delegate class is


nit: What's a raster widget? My name is snapshot widget!

goderbauer · 2022-08-18T18:28:44Z

packages/flutter/lib/src/widgets/snapshot_widget.dart

+    final SnapshotPainter oldPainter = painter;
+    oldPainter.removeListener(markNeedsPaint);
+    _painter = value;
+    if (painter.shouldRepaint(oldPainter)) {


if painter and oldPainter have different runtimetypes you probably always want to repaint without asking shouldRepaint similarly to how CustomPaint does it?

…to snapshot_widget

flutter-dashboard · 2022-08-23T22:42:21Z

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Changes reported for pull request #109485 at sha 8fd8693

jonahwilliams · 2022-08-24T20:29:42Z

I've updated the PR based on the last round of comments

goderbauer

LGTM

goderbauer · 2022-08-24T23:11:32Z

packages/flutter/test/widgets/snapshot_widget_test.dart

+    expect(painter.count, 1);
+  }, skip: kIsWeb); // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689
+
+


nit: remove one blank line?

goderbauer · 2022-08-24T23:11:42Z

packages/flutter/test/widgets/snapshot_widget_test.dart

+    expect(tester.layers.last, isA<PictureLayer>());
+  }, skip: kIsWeb); // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689
+
+


goderbauer · 2022-08-24T23:11:59Z

packages/flutter/test/widgets/snapshot_widget_test.dart

+}
+
+class TestPainter2 extends TestPainter {
+    @override


nit: indentation

…lutter/flutter#109485)

[framework] simplify raster widget

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		expect(painter.count, 1);
		}, skip: kIsWeb); // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689

		expect(tester.layers.last, isA<PictureLayer>());
		}, skip: kIsWeb); // TODO(jonahwilliams): https://github.com/flutter/flutter/issues/106689

[framework] simplify raster widget, rename, combine painters #109485

[framework] simplify raster widget, rename, combine painters #109485

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jonahwilliams commented Aug 13, 2022 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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goderbauer commented Aug 15, 2022

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jonahwilliams commented Aug 13, 2022 •

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