'Paint' method for HTML5 Canvas?

Is there a way of preventing anything drawn to the canvas to be see开发者_开发知识库n until a certain point? I'd like to be able to draw a number of objects at once, then draw over them with another object and a different composite method, on a loop.

Because the first lot of painting takes so long, the result will only be seen for a fraction of a second before it loops.

The normal method would be to render those objects into an off-screen Canvas, and then use context.drawImage() to copy it onto the on-screen one.