void setup()
{
  size(640, 480);
  background(245);
  smooth();
 for (int i = 0; i < 640; i=i+30) {
    line(0, i, 640, i);
    line( i,0, i,640);
    stroke(0);
  }
}

void draw() 
{
  line(mouseX++, mouseY++, pmouseX++, pmouseY++);
  if  (mouseY > 60){
     stroke (255, 0, 0);
   }else {
     stroke (0); 
   }
}

void mousePressed() {
 background(245);
 for (int i = 0; i < 640; i= i+30) {
    line(0, i, 640, i);
  line( i,0, i,640);
  stroke(10);
}
}

void lineTool(int x, int y, int px, int py) 
{
  float speed = abs(x-px) + abs(y-py);
  stroke(speed);
  line(x, y, speed++, speed++);
}