Processing, Line Drawing Program, Simplest

linedraw.pde

//draw a contiuous line

void setup() {
  size(500,500);
  background(0,0,0);
}

void draw() {
  stroke(255,255,255);
  line(pmouseX, pmouseY, mouseX, mouseY);
  println("Mouse X: " + mouseX + " Mouse Y: " + mouseY);
  
}