Methods, systems, and apparatus, including computer program products, for incrementally updating the rendering of an artwork. In one aspect, a method includes first drawing a first portion of an artwork in a view, accepting input to draw a second portion of the artwork in the view, the second portion including a first region and a second region, stopping the first drawing before completion at a first level of completion, second drawing the second region in the view until progress of the second drawing reaches a second level of completion that is approximately the same as the first level of completion, joining the first region and the second region into a third region, and third drawing the third region in the view where the third drawing resumes drawing of the first and second regions at their respective levels of completion.