SnapshotWidget class

A widget that can replace its child with a snapshotted version of the child.

A snapshot is a frozen texture-backed representation of all child pictures and layers stored as a ui.Image.

This widget is useful for performing short animations that would otherwise 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 itself and manipulated instead.

For example, the Android Q ZoomPageTransitionsBuilder uses a snapshot widget for the forward and entering route to avoid the expensive scale animation. This also has the effect of briefly pausing any animations on the page.

Generally, this widget should not be used in places where users expect the child widget to continue animating or to be responsive, such as an unbounded animation.

Caveats:

• The contents of platform views cannot be captured by a snapshot widget. If a platform view is encountered, then the snapshot widget will determine how to render its children based on the SnapshotMode. This defaults to SnapshotMode.normal which will throw an exception if a platform view is encountered.

• The snapshotting functionality of this widget is not supported on the HTML backend of Flutter for the Web. Setting SnapshotController.allowSnapshotting to true may cause an error to be thrown. On the CanvasKit backend of Flutter, the performance of using this widget may regress performance due to the fact that both the UI and engine share a single thread.