Op 3-5-2012 14:24, Laurine Harbulot schreef:
Hello all,
We're students and we're working on a space invaders project.
Our game runs very well but we've got a problem:
We would like to give the opportunity to players to press two
keyboards buttons at the same time but for now,our program tests only
one event at the same time.
Is there a solution for that ?
Thanks all.
Laurine and Vincent
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Hello,
If I look at this text copied from htpd2e it can't.
Once the big-bang
<http://docs.racket-lang.org/teachpack/2htdpuniverse.html#%28form._%28%28lib._2htdp%2Funiverse..rkt%29._big-bang%29%29>
expression is evaluated, DrRacket acts just like a real operating
system, watching the clock, the key board, and the mouse for events and
dispatching to your designated BSL functions.
The key question is what arguments DrRacket supplies to your event
handlers for key strokes, mouse clicks, and clock ticks and what kind of
results it expects from these event handlers. Like a real operating
system, DrRacket gives these functions access to the current state of
the world. For key events and mouse events, DrRacket also supplies
information about these events.
The initial state is the value of w0, because our big-bang
<http://docs.racket-lang.org/teachpack/2htdpuniverse.html#%28form._%28%28lib._2htdp%2Funiverse..rkt%29._big-bang%29%29>
expression says so. It also is the state that DrRacket hands to the
first event handling function that it uses. DrRacket expects that this
event handling function produces a new state of the world, and DrRacket
keeps this result around until the second event happens. Here is a table
that describes this relationship among worlds and event handling functions:
event:
big-bang
<http://docs.racket-lang.org/teachpack/2htdpuniverse.html#%28form._%28%28lib._2htdp%2Funiverse..rkt%29._big-bang%29%29>
e1
e2
e3
e4
current world:
w0
w1
w2
w3
w4
clock tick:
(cthw0)
(cthw1)
(cthw2)
(cthw3)
(cthw4)
key stroke:
(kehw0...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(kehw1...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(kehw2...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(kehw3...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(kehw4...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
mouse click:
(mehw0...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(mehw1...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(mehw2...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(mehw3...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
(mehw4...
<http://docs.racket-lang.org/htdp-langs/beginner.html#%28form._%28%28lib._lang%2Fhtdp-beginner..rkt%29._......%29%29>)
Although you might imagine that two events happen at the same time,
DrRacket arranges all events in a linear sequence.The first row
enumerates the events since DrRacket started evaluating the big-bang
<http://docs.racket-lang.org/teachpack/2htdpuniverse.html#%28form._%28%28lib._2htdp%2Funiverse..rkt%29._big-bang%29%29>
expression, while the second row presents the current world---a result
of processing the event. The big-bang
<http://docs.racket-lang.org/teachpack/2htdpuniverse.html#%28form._%28%28lib._2htdp%2Funiverse..rkt%29._big-bang%29%29>
column thus says that w0 becomes the current world as a result of a
big-bang
<http://docs.racket-lang.org/teachpack/2htdpuniverse.html#%28form._%28%28lib._2htdp%2Funiverse..rkt%29._big-bang%29%29>
event. Each of the remaining rows tabulates what the functions cth, keh,
and meh produce when applied to the current world. Only one of these
results is chosen, however, as the current world---depending on which
event actually takes place.
So suppose e1 is the key stroke "a", e2 and e3 are clock ticks, and e3
is a mouse event. Then
1.
w1 is the result of (kehw0"a"), i.e., the fourth cell in the e1 column;
2.
w2 is the result of (cthw1), i.e., the third cell in the e2 column;
3.
w3 is (cthw2), i.e., again the third cell in the e3 column; and
4.
(mehw390100"button-down") produces w4 assuminge4 is the mouse event
"button down" taking place at the position (90,100).
Roelof
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