[plt-scheme] HTDP Extended Exercise: Interactive Games

From: Connor Ferguson (psfreak at linkline.com)
Date: Mon Mar 8 21:07:24 EST 2004


Sorry to take so long to get back to you. If draw-scene draws the AUP and
UFO and draws and clears the shot, what would clear-scene do? Would it need
to do anything with the shot, since draw-scene has already cleared it from
the canvas?


on 3/7/04 10:19 AM, Matthias Felleisen at matthias at ccs.neu.edu wrote:

> On Mar 6, 2004, at 6:55 PM, Connor Ferguson wrote:
>> For list-related administrative tasks:
>> http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>> I am working on the extended exercise for HTDP: Interactive Games
>> (http://www.ccs.neu.edu/home/matthias/HtDP/Extended/igames.html). In
>> Exercise 2.4.5, it says to modify draw-scene and clear-scene to also
>> consume
>> a Shot/f. What do they do with this shot (draw it, move it?)?
> What did draw-scene and clear-scene do before? According to 2.3.2 (the
> pointer in 2.4.5),
>> Design the function draw-scene. It consumes an AUP and a UFO and draws
>> them on the canvas.
>> Also design clear-scene, which consumes a AUP and a UFO and clears
>> them from the canvas.
> So I'd say that draw-scene now draws and clears the shot, if it has
> been fired.
> Hint: If the shot/f argument is false, no shot has been fired. Later
> you will see that it is -- as often -- easier to deal with the
> generalization of the problem, when you draw an entire list of shots
> per scene. Then, when no shot has been fired, you just get empty.
> -- Matthias

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