来源$ C ​​$下的Javascript树，具有在＆QUOT;发明的原理及QUOT;视频 [英] Source code for Javascript tree that features in "Inventing on Principle" video

问题描述

我是相当受布雷维克多对原理的视频发明灵感（http://vimeo.com/36579366）。

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

另外，我非常使用Javascript得出，树迷住了。我没有做太多的图形编程。我所有的生涯中，我一直是中间层和数据库开发人员。但看着那编程画树，我主动地学习。我已经开始学习JavaScript。我知道我最终会（在数周或数月，取决于多少时间，我弄）能够从头开始编写这样的程序我自己。

Also, I was very fascinated by that tree drawn using Javascript. I have not done much of graphics programming. All my career I have been a middle-tier and database developer. But looking at that programmatically draw tree, I am motivated to learn. I have started learning Javascript. I know I will eventually (in a few weeks or months, depending on how much time I get) be able to write such program myself from scratch.

不过，我真的很渴望得到一些源$ C ​​$ C，做类似图中的Javascript和它玩。任何链接/指针你们能提供将是非常有益的。

However, I am really really eager to get some source code that does similar drawing in Javascript and play with it. Any links/pointers you guys can provide would be very useful.

推荐答案

画一棵树与画布是很简单的。请参阅下面的约80行code的解决方案。

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

有几个人已经开始尝试重新建立从视频的互动环境。 其中一个是由 GitHub的用户tnlogy尝试。他的环境，让您选择一个号码在code和使用滑块改变运行演示上即时。我分叉了code，包括树演示。

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.

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

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

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 = $('<canvas width="' + width + '" height="' + height + '"></canvas>'),
  ctx = canvas[0].getContext("2d");

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

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