Canvas class abstract

An interface for recording graphical operations.

Canvas objects are used in creating Picture objects, which can themselves be used with a SceneBuilder to build a Scene. In normal usage, however, this is all handled by the framework.

A canvas has a current transformation matrix which is applied to all operations. Initially, the transformation matrix is the identity transform. It can be modified using the translate, scale, rotate, skew, and transform methods.

A canvas also has a current clip region which is applied to all operations. Initially, the clip region is infinite. It can be modified using the clipRect, clipRRect, and clipPath methods.

The current transform and clip can be saved and restored using the stack managed by the save, saveLayer, and restore methods.

Use with the Flutter framework

The Flutter framework's RendererBinding provides a hook for creating Canvas objects (RendererBinding.createCanvas) that allows tests to hook into the scene creation logic. When creating a Canvas that will be used with a PictureLayer as part of the Scene in the context of the Flutter framework, consider calling RendererBinding.createCanvas instead of calling the Canvas.new constructor directly.

This does not apply when using a canvas to generate a bitmap for other purposes, e.g. for generating a PNG image using Picture.toImage.