processing4/java/examples/Topics/Drawing/ContinuousLines/ContinuousLines.pde

/**
 * Continuous Lines. 
 * 
 * Click and drag the mouse to draw a line. 
 */
 
void setup() {
  size(640, 200);
  background(102);
}

void draw() {
  stroke(255);
  if(mousePressed) {
    line(mouseX, mouseY, pmouseX, pmouseY);
  }
}