For a project in my class we have to design a little game, but using no global variable. I'm still very new to Processing and programming in general so I can't really think of a way to do this. Since draw re-run infinitely and setup is only run once I can't find a way to make something as simple as having a square move up when a key is pressed.

A rough outline I have is that

player hero;

void setup()
{
 size(400,400);
 background(255);
 hero = new player(50,200,300);
}

void draw()
{
if ( keyPressed & (key == 'w') )
{
  hero.move();
}
}

class player {

int sSize;
int xPos;
int yPos;

player(int size_, int xPos_, int yPos_)
{
  sSize = size_;
  xPos = xPos_;
  yPos = yPos_;
  background(255);
  stroke(0);
  fill(155);
  rectMode(CENTER);
  rect(xPos,yPos,sSize,sSize);
}

void move()
{
 yPos--;
 background(255);
 stroke(0);
 fill(155);
 rectMode(CENTER);
 rect(xPos,yPos,sSize,sSize);
}

}


Is there a different way to achieve this w/o using global variable?

Also is there a way to move the square w/o having to redraw the background? like remove the previous square somehow? because the background will be a room with a random placement for the door, if draw runs the function again then the door might be in a different location.

If any clarifying needs to be done, please let me know.

Thanks!

Thanks for your reply blindfish!
Fortunately the teacher allowed us to use global variable now. Indeed I think he was trying to make us avoid declaring regular primitive data type, even so I would feel weird using a global object variable if he doesn't want -any- global. Luckily he changed his mind. : )

For the second part can you clarify what you mean by attach the keyPressed & keyReleased function into the classes? I have tried, and perhaps I'm doing it wrong, but it didn't really worked out the way I anticipated.

A snippet of what I did:

player hero = new player();

void draw()
{
  hero.keyPressed();
  hero.keyReleased();
}

class player
{
  int n, s, e, w;  
 
 void keyPressed()
 {    
   //very redundent a way to reduce code possible?
   println(key);
   switch (key)
   {
     case 'w': n = 1; break;
     case 'a': w = 1; break;
     case 's': s = 1; break;
     case 'd': e = 1; break;
     case 'W': n = 3; break;
     case 'A': w = 3; break;
     case 'S': s = 3; break;
     case 'D': e = 3; break;
   }
   if (n > 0)
   {
     yPos = yPos - n*2;
   }
   if (w > 0)
   {
     xPos = xPos - w*2;
   }
   if (s > 0)
   {
     yPos = yPos + s*2;
   }
   if (e > 0)
   {
     xPos = xPos + e*2;
   }
   
   drawOut(xPos, yPos);
 }
 
 void keyReleased()
 {
   switch (key)
   {
     case 'w': n = 0; break;
     case 'a': w = 0; break;
     case 's': s = 0; break;
     case 'd': e = 0; break;
     case 'W': n = 0; break;
     case 'A': w = 0; break;
     case 'S': s = 0; break;
     case 'D': e = 0; break;
   }
 }

 void drawOut()
 {
   //draws player
  }

}
The problem I encounter is when a key is pressed the hero.keyPressed() is ran repeatedly since it's in draw. I must be implementing it wrong. What I did now it remove the keyPressed and keyReleased from the class and into a function of its own.

Is the way I did it in the example above what you were saying, but I just did it wrong? Thanks.