var startY;

var lineStart = false;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(255, 200, 200)

  if (lineStart) {

    var lineLen = Math.sqrt(Math.pow((mouseY - startY), 2)

                            + Math.pow((mouseX - startX), 2));

    var numSeg = lineLen/10;

    var xStep = (mouseX - startX) / numSeg;

    var yStep = (mouseY - startY) / numSeg;

    var lastX = startX;

    var lastY = startY;

    var currX, currY;

    var currSeg = 0;

    while (currSeg < numSeg) {

      if (currSeg % 2 == 0) {

        currX = lastX + xStep;

        currY = lastY + yStep;

        if (Math.abs(currX - startX) >= Math.abs(mouseX - startX)) {

          currX = mouseX;

          currY = mouseY;

        }

        line(lastX, lastY, currX, currY);

      }

      lastX += xStep;

      lastY += yStep;

      currSeg ++;

    }

  }

}

​

function mousePressed() {

  startX = mouseX;

  startY = mouseY;

  lineStart = true;

}