Robby -- I don't know enough about how the internal drawing routine of DrRacket works, so you could help clarify that.
In 2htdp/universe, the act of "movement" is represented by reconstructing the entire scene. Of course, there may be sharing: (define bg ... something complex ...) ;; at time 1 (place-image I 50 50 bg) ;; at time 2 (place-image I 70 70 bg) When this is finally rendered as a single image in the window, how much work is done? Is it proportional to the size of the scene, or is it only proportional to the pixels that changed between the scene at time 1 and the scene at time 2? Does the library perform a diff between the two scene graphs? In Whalesong's web-world, the act of "movement" is represented by a cursor finding the object and functionally updating its CSS. After web-world does its tree-diff, it uses a *mutative update* to change the CSS attributes. My understanding is that the browser DOM implementation then uses this information to update the screen as efficiently as possible (using Z depth to avoid unnecessary redraws, clipping, bitblit, etc). Thus, in web-world, the amount of work should be proportional to the number of affected pixels and *independent* of the number of unaffected ones. Is this true of 2htdp/image/universe? Shriram _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
