BackdropFilter class Null safety

A widget that applies a filter to the existing painted content and then paints child.

The filter will be applied to all the area within its parent or ancestor widget's clip. If there's no clip, the filter will be applied to the full screen.

The results of the filter will be blended back into the background using the blendMode parameter. The only value for blendMode that is supported on all platforms is BlendMode.srcOver which works well for most scenes. But that value may produce surprising results when a parent of the BackdropFilter uses a temporary buffer, or save layer, as does an Opacity widget. In that situation, a value of BlendMode.src can produce more pleasing results, but at the cost of incompatibility with some platforms, most notably the html renderer for web applications.

link
If the BackdropFilter needs to be applied to an area that exactly matches its child, wraps the BackdropFilter with a clip widget that clips exactly to that child. 
Stack(
  fit: StackFit.expand,
  children: <Widget>[
    Text('0' * 10000),
    Center(
      child: ClipRect(  // <-- clips to the 200x200 [Container] below
        child: BackdropFilter(
          filter: ui.ImageFilter.blur(
            sigmaX: 5.0,
            sigmaY: 5.0,
          ),
          child: Container(
            alignment: Alignment.center,
            width: 200.0,
            height: 200.0,
            child: const Text('Hello World'),
          ),
        ),
      ),
    ),
  ],
)

This effect is relatively expensive, especially if the filter is non-local, such as a blur.

If all you want to do is apply an ImageFilter to a single widget (as opposed to applying the filter to everything beneath a widget), use ImageFiltered instead. For that scenario, ImageFiltered is both easier to use and less expensive than BackdropFilter.

See also:

Inheritance

Constructors

BackdropFilter({Key? key, required ImageFilter filter, Widget? child, BlendMode blendMode = BlendMode.srcOver})
Creates a backdrop filter.
const

Properties

blendMode → BlendMode
The blend mode to use to apply the filtered background content onto the background surface.
final
child → Widget?
The widget below this widget in the tree.
finalinherited
filter → ImageFilter
The image filter to apply to the existing painted content before painting the child.
final
hashCode → int
The hash code for this object.
nonVirtual">@nonVirtualread-onlyinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType → Type
A representation of the runtime type of the object.
read-onlyinherited

Methods

createElement() → SingleChildRenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
inherited
createRenderObject(BuildContext context) → RenderBackdropFilter
Creates an instance of the RenderObject class that this RenderObjectWidget represents, using the configuration described by this RenderObjectWidget.
override
debugDescribeChildren() → List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
protected">@protectedinherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
didUnmountRenderObject(covariant RenderObject renderObject) → void
A render object previously associated with this widget has been removed from the tree. The given RenderObject will be of the same type as returned by this object's createRenderObject.
protected">@protectedinherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed.
inherited
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) → String
A string representation of this object.
inherited
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String
Returns a string representation of this node and its descendants.
inherited
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String
Returns a one-line detailed description of the object.
inherited
toStringShort() → String
A short, textual description of this widget.
inherited
updateRenderObject(BuildContext context, covariant RenderBackdropFilter renderObject) → void
Copies the configuration described by this RenderObjectWidget to the given RenderObject, which will be of the same type as returned by this object's createRenderObject.
override

Operators

operator ==(Object other) → bool
The equality operator.
nonVirtual">@nonVirtualinherited