Source code for Javascript tree that features in “Inventing on Principle” video

Question

I was quite inspired by Bret Victor\'s Inventing on Principle video (http://vimeo.com/36579366).

Also, I was very fascinated by that tree drawn using Javascript. I

Answer 1

Drawing a tree with the canvas is simple enough. See below for a solution in about 80 lines of code.

Several people have started attempts at re-creating the interactive environment from the video. One of those attempts was made by github user tnlogy. His environment allows you to select a number in the code and change the running demo on-the-fly using a slider. I've forked his code to include a tree demo.

Demo for interactive tree:

http://brianpeiris.github.com/live-coding/

Demo for simple tree:

http://jsfiddle.net/brianpeiris/v9zD6/show

Source for simple tree demo

var
  drawLeaf = function (cx, xx, yy) {
    var
      leafAlpha = 8/10,
      leafSize = 7;

    cx.beginPath();
    cx.fillStyle = (
      "rgba(" + 
      Math.round(220 + (Math.random() * 50)) + ", " + 
      Math.round(180 + (Math.random() * 50)) + ", " + 
      Math.round(220 + (Math.random() * 50)) + ", " + 
      leafAlpha + 
      ")"
    );  
    cx.arc(xx, yy, leafSize, 0, Math.PI * 2);
    cx.fill();
  },
  drawBranch = function (ii, cx, xx, yy, level, levels, angle, numBranches) {
    var
      branchLength = 44,
      subBranchWidthFactor = 2,
      sweep = Math.PI * 25/30,
      branchTweakMagnitude = 52/50,
      tt;

    cx.beginPath();

    // Draw thinner branches away from the trunk
    cx.lineWidth = (levels - level) * subBranchWidthFactor;

    // Calculate the angle of the branch, with some random tweaks
    tt = (
      sweep * ii / (numBranches - 1) + angle -
      sweep / 2 + Math.PI + 
      Math.random() * 0.5 * branchTweakMagnitude
    );

    cx.moveTo(xx, yy);
    newXX = xx + Math.sin(tt) * branchLength;
    newYY = yy + Math.cos(tt) * branchLength;
    cx.lineTo(newXX, newYY);
    cx.stroke();

    // Recursively draw more branches
    drawBranchesAndLeaves(cx, newXX, newYY, level + 1, levels, Math.PI + tt);
  },
  drawBranchesAndLeaves = function (cx, xx, yy, level, levels, angle) {
    var
      numBranches = 5,
      ii, newXY;

    // This function is called recursively. The recursion terminates when we
    // have reached the specified number of recursive levels.
    if (level === levels) { 
      drawLeaf(cx, xx, yy);
      return; 
    }
    else {
      for (ii = 0; ii < numBranches; ii++) {
        drawBranch(ii, cx, xx, yy, level, levels, angle, numBranches);
      }
    }
  },

  drawTree = function(cx, ww, hh) {
    var trunkX = ww / 2, trunkY = hh - 165;

    cx.strokeStyle = "black";
    cx.lineWidth = 13;
    cx.lineCap = "round";

    cx.moveTo(trunkX, hh);
    cx.lineTo(trunkX, trunkY);
    cx.stroke();

    drawBranchesAndLeaves(cx, trunkX, trunkY, 0, 3, 0);
  },
  width = 350,
  height = 350,
  canvas = $(''),
  ctx = canvas[0].getContext("2d");

  $('body').append(canvas);
  drawTree(ctx, width, height);