void setup() { 
  size(1200,1200); 
  background(255); 
  smooth();
  stroke(0,0,0,50); 

}

void draw() 
{ 
    stroke(abs(mouseX-pmouseX )); 
   strokeWeight(abs(mouseX-pmouseX ) );
  line(pmouseX,pmouseY,mouseX,mouseY);
}