key event troubles

in Programming Questions • 1 year ago

I'm trying to create a simple application where a rect is drawn on the screen and moved by keys. 'a' is supposed to move the rect down while 's' is supposed to move it upwards. For some reason after I press 'a' and the rect stops at the bottom, 's' takes over and key 'a' becomes unresponsive... Any ideas how the sketch could be improved?

PVector loc;

PVector acc;

PVector acc2;

boolean stop, a, s;

void setup() {

size(400, 400);

loc = new PVector(200, 200);

acc = new PVector(0, 3);

//acc2 = new PVector(0, -1);

}

void draw() {

background(255);

rect(loc.x, loc.y, 30, 30);

if (a) {

loc.add(acc);

}

if (s) {

loc.sub(acc);

}

if (loc.y>height-30) {

loc.y = height-30;

}

else if (loc.y<=0) {

loc.y=0;

}

if (s) {

loc.sub(acc);

}

println(loc.y);

}

void keyPressed() {

if (key == 'a') {

a=!a;

}

if (key == 's') {

s=!s;

}

Replies(4)

PhiLho

Re: key event troubles

1 year ago

The base logic is flawed. You can have both a and s active at the same time.
BTW, the choice of keys is strange, on my keyboard, a is above s...

(that's why I don't like the wsad commands, I prefer good old arrow keys).
And you have s acting twice in your code.

Manindra29

Re: key event troubles

1 year ago

You need to reset the boolean variables a and s, once the rectangle reaches the edge of the window. Minor bug.

Here's the complete corrected code:

PVector loc;
PVector acc;
PVector acc2;
boolean stop, a, s;
void setup() {
size(400, 400);
loc = new PVector(200, 200);
acc = new PVector(0, 3);
a = s = false; //It is a good practice to initialize variables
//acc2 = new PVector(0, -1);
}
void draw() {
background(255);
rect(loc.x, loc.y, 30, 30);
if (a) {
loc.add(acc);
}
if (s) {
loc.sub(acc);
}
if (loc.y>height-30) {
loc.y = height-30;
a = !a; //reset a
}
else if (loc.y<=0) {
loc.y=0;
s = !s; //reset s
}
println(loc.y);
}
void keyPressed() {
if (key == 'a') {
a=!a;
}
if (key == 's') {
s=!s;
}
}

alkopop79

Re: key event troubles

1 year ago

Thanks very much! That's great!

PhiLho

Re: key event troubles

1 year ago

The logic is still flawed: if I hit s, it goes up. If I then hit a, it stops. Hitting a again, it goes up!
See http://wiki.processing.org/w/Multiple_key_presses wiki page for a more suitable even handling: it distinguishes key up and key down events.

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