In this demonstration, two equivalent pieces of code show off using either the canvas primitives, or their SVG equivalents, to draw a filled enclosed polygon of two arcs about a centerpoint. I wrote this mainly as a testbed for another project. In chrome, the linear gradient for canvas is rather buggy, and will flicker sometimes.
Also, despite the demo_container class being clearly defined with a height and width, setting the canvas to match that occasionally fails, and the drawing will be mangled.