[plt-scheme] HTDP Extended Exercise: Interactive Games

On Mar 8, 2004, at 9:52 PM, mathematica wrote:

>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>
> Please don't mind that I reply.

Never. I love it when "students" help each other.

>
> ;; SHOT is a Posn
> ;; SHOT/f is SHOT of false, false indicate that now there is no shot
>
> draw-scene only draw the AUP, UFO and SHOT. It is clear-scene which 
> clear AUP, UFO and SHOT
>

Yes.

-- Matthias


>
> --  mathematica
>
>>
>> Matthias-
>>
>> 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?
>>
>> -Connor
>>
>> 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
>>>
>