CustomPaint class

A widget that provides a canvas on which to draw during the paint phase.

When asked to paint, CustomPaint first asks its painter to paint on the current canvas, then it paints its child, and then, after painting its child, it asks its foregroundPainter to paint. The coordinate system of the canvas matches the coordinate system of the CustomPaint object. The painters are expected to paint within a rectangle starting at the origin and encompassing a region of the given size. (If the painters paint outside those bounds, there might be insufficient memory allocated to rasterize the painting commands and the resulting behavior is undefined.) To enforce painting within those bounds, consider wrapping this CustomPaint with a ClipRect widget.

Painters are implemented by subclassing CustomPainter.

Because custom paint calls its painters during paint, you cannot call setState or markNeedsLayout during the callback (the layout for this frame has already happened).

Custom painters normally size themselves to their child. If they do not have a child, they attempt to size themselves to the specified size, which defaults to Size.zero. The parent may enforce constraints on this size.

The isComplex and willChange properties are hints to the compositor's raster cache.

{@tool snippet}

This example shows how the sample custom painter shown at CustomPainter could be used in a CustomPaint widget to display a background to some text.

CustomPaint(
  painter: Sky(),
  child: const Center(
    child: Text(
      'Once upon a time...',
      style: TextStyle(
        fontSize: 40.0,
        fontWeight: FontWeight.w900,
        color: Color(0xFFFFFFFF),
      ),
    ),
  ),
)

{@end-tool}

See also:

  • CustomPainter, the class to extend when creating custom painters.
  • Canvas, the class that a custom painter uses to paint.
Inheritance

Constructors

CustomPaint({Key? key, CustomPainter? painter, CustomPainter? foregroundPainter, Size size = Size.zero, bool isComplex = false, bool willChange = false, Widget? child})
Creates a widget that delegates its painting.
const

Properties

child → Widget?
The widget below this widget in the tree.
final
foregroundPainter → CustomPainter?
The painter that paints after the children.
final
hashCode → int
The hash code for this object.
no setterinherited
isComplex → bool
Whether the painting is complex enough to benefit from caching.
final
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
painter → CustomPainter?
The painter that paints before the children.
final
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
size → Size
The size that this CustomPaint should aim for, given the layout constraints, if there is no child.
final
willChange → bool
Whether the raster cache should be told that this painting is likely to change in the next frame.
final

Methods

build(BuildContext context) → Widget
Describes the part of the user interface represented by this widget.
override
createElement() → StatelessElement
Creates a StatelessElement to manage this widget's location in the tree.
inherited
debugDescribeChildren() → List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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, int wrapWidth = 65}) → 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

Operators

operator ==(Object other) → bool
The equality operator.
inherited