How can I fill the screen with a given square?

Processing Coding Questions
1

So at first click nothing happens than, at the second click a square appears from the line of the te two click coordinates, After this i have to fill this square, this is ok I did this.
Now how can I fill the screen like this ?
“1” is the first click, “2” is the second click.
ecample

My code so far:

boolean first=true; boolean done = false;
int x1,x2,y1,y2,xl,yl,x3,y3,x4,y4;

void setup(){
  size(640,480);
}

void draw(){
  background(240);
  if(done){
    if(x1 <= x2){
      //draw left     
      if(y1 <=y2){
        yl = y2-y1;
        xl = x2-x1;
        szR(x1,y1,x2,y2);
        x3 = x1-yl; y3 =y1+xl;
        szR(x1,y1,x3,y3);
        x4 = x2-yl; y4 = y2+xl;
        szR(x2,y2,x4,y4);
        szR(x3,y3,x4,y4);
        scanLine();
        
      }else{
        yl = y2-y1;
        xl = x1-x2;
        szR(x1,y1,x2,y2);
        x3 = x1-yl; y3 =y1-xl;
        szR(x1,y1,x3,y3);
        x4 = x2-yl; y4 = y2-xl;
        szR(x2,y2,x4,y4);
        szR(x3,y3,x4,y4);
        scanLine();  
    }
   }else{
     //draw right
     if(y1 <=y2){
        yl = y1-y2;
        xl = x1-x2;
        szR(x1,y1,x2,y2);
        x3 = x1+yl; y3 =y1-xl;
        szR(x1,y1,x3,y3);
        x4 = x2+yl; y4 = y2-xl;
        szR(x2,y2,x4,y4);
        szR(x3,y3,x4,y4);
        scanLine();
      }else{
        yl = y1-y2;
        xl = x2-x1;
        szR(x1,y1,x2,y2);
        x3 = x1-yl; y3 =y1-xl;
        szR(x1,y1,x3,y3);
        x4 = x2-yl; y4 = y2-xl;
        szR(x2,y2,x4,y4);
        szR(x3,y3,x4,y4);
        scanLine();
      }
   }
  }
}

void mousePressed(){
if(first){
    x1 = mouseX;
    y1 = mouseY;
    first= false;
    done = false;
  }else{
    x2 = mouseX;
    y2 = mouseY;
    done = true;
    first = true;
  }
}

void scanLine(){
  boolean start = true;
  color x;
  int x1 = -1,y1 = -1,x2 = -1,y2 = -1;
  for(int i = 0; i < 480; i++){
    for(int j = 0; j < 640;j++){
        x = get(j,i);
        if(x == color(30) && start){
          x1 = j; y1 = i;
          x2 = j; y2 = i;
          start = false;
        }else if(x == color(30) && !start){
          x2 = j; y2 = i;
        }
    }
    if(x1 >= 0){
      szR(x1,y1,x2,y2);
    }
    x1 = -1;y1 = -1;x2 = -1;y2 = -1;
    start = true;
  }
  
}
void szR(int xa, int ya, int xb,int yb){
  float x1 = (float) xa; float y1 = (float) ya;
  float x2 = (float) xb; float y2 = (float) yb;
  float x = x1; float y = y1;
  float m;
  m=(y1-y2)/(x1-x2);
  if(abs(m)<=1)
  {
    if(x1<x2)
    {
      for(x=x1;x<=x2;x++)
      {
        point(x,y);
        y=y+m;
      }
    }
    if(x2<x1)
    {
      for(x=x1;x>=x2;x--)
      {
        point(x,y);
        y=y-m;
      }
    }
  }
  if(abs(m)>1)
  {
    if(y1<y2)
    {
      for(y=y1;y<=y2;y++)
      {
        point(x,y);
        x=x+(1/m); 
      }
    }
     if(y2<y1)
    {
      for(y=y1;y>=y2;y--)
      {
        point(x,y);
        x=x-(1/m); 
      }
    }
  }
};
2

Very useful advice. I think I’ll try it