Shape behavior

What a person can do to a shape comes from its definition in pure Dart. The engine and the Flutter canvas read the same declaration; an overlay never decides on its own whether an operation is allowed. Part of it you declare as behavior; the rest follows from the shape's anatomy.

Declare behavior

import 'package:vyuh_diagram_core/extension_api.dart';
import 'package:vyuh_diagram_core/vyuh_diagram_core.dart';

final note = ShapeDefinition(
  type: 'app.note',
  size: const DiagramSize(240, 120),
  behavior: const ShapeBehavior(
    rotatable: false,
    textSizing: ShapeTextSizing.fitHeight,
  ),
  body: const ShapeText('body', text: 'Height follows the text'),
);

The note cannot rotate, and its height follows its text, so only its left and right resize handles show.

ShapeBehavior property	Default	Effect
selectable	true	Whether the shape can be selected.
deletable	true	Whether the shape can be deleted.
movable	true	Whether the shape can be moved.
resizable	true	Whether the shape can be resized; false shows no resize handles.
rotatable	true	Whether the shape can be rotated, from a corner or the rotation handle.
rotationHandle	false	Shows a stem-and-circle rotation control above a rotatable shape.
textSizing	ShapeTextSizing.fixed	fixed keeps the authored frame; growHeight treats the authored height as a minimum and grows downward; fitHeight makes the height follow the content exactly.

Resize handles follow from these: all eight when resizable, only the left and right sides when the height fits the content, and none when not resizable. behavior.resizeHandles lists them. Handle names describe the shape's local sides; their positions follow shape rotation. The rotation stem is presentation only: it cannot enable rotation when rotatable is false.

What follows from the anatomy

Editing is not declared with flags. It follows from what the shape is made of:

The shape has	So a person can edit	Read it as
An outline	Fill and stroke	definition.paintsSurface
An outline that rounds its corners (rect(), regularPolygon(), editablePath(), or a path with cornerRadius: true)	Corner radius	definition.cornerRadiusEditable
An editable ShapeText, or content such as a table	Text	definition.textEditable
A PathValueField read by an editable path outline	Points	definition.pathValue
A regular polygon outline	Its number of sides	definition.sidesValue
An ImageValueField	The image	definition.imageValue
Any other value	That value, with one control each	definition.customValues

definition.propertyEditors lists the resulting inspector sections in order. To remove a control, change the anatomy: a shape with outline: null has no fill or stroke, ShapeOutline.rect(cornerRadius: false) has square corners, a ShapeText(..., editable: false) is text people cannot edit on the canvas, and body: null hosts no text.

Containers

A shape that owns child elements declares a container:

import 'package:vyuh_diagram_core/extension_api.dart';

final lane = ShapeDefinition(
  type: 'app.lane',
  container: const ShapeContainer(clips: true, resizesChildren: false),
  behavior: const ShapeBehavior(rotatable: false),
);

ShapeContainer property	Default	Effect
clips	false	Instances may clip their children to the outline with clipContent. A clipping container always shows its border, so its extent stays visible.
resizesChildren	true	Whether resizing the container scales its children. Movement and rotation always carry them.

A container may also declare collapse: ShapeCollapseDefinition(...) for a compact presentation. See frames and ownership.

Definition policy versus instance state

Behavior is fixed on each registered definition; there is no per-instance behavior callback. Locking an instance keeps it selectable but stops moving, resizing, rotating, deleting and editing it, while preserving its appearance. A collapsed container cannot resize or rotate, and its text does not size it. Content can narrow behavior too: a table whose controls disable resizeTable makes its shape not resizable. resolved.behavior on a resolved shape combines all of these. Command admission additionally checks the diagram's DiagramRules and operation preconditions.

For a different permanent behavior, register another shape definition. Do not replace a loaded registry definition or hide handles in an overlay as a substitute for engine policy.

See shape anatomy to package this definition in an extension and Canvas foundations to render it.