on-paint

Called when the canvas is exposed or resized so that the image in the canvas can be repainted.

When on-paint is called in response to a system expose event and only a portion of the canvas is newly exposed, any drawing operations performed by on-paint are clipped to the newly-exposed region; however, the clipping region as reported by get-clipping-region does not change.

• (send a-canvas on-paint) -> void

  Does nothing.