I am not able to draw shapes except for random lines onthe canvas. What will be the code for other options eg any line, rectangle or a triangle?

<script type="text/javascript">
 var canvas, context, tool, e;
 var varblurup=0;
 var varsizeup=1;
   var swtchclr;
  // Keep everything in anonymous function, called on window load.

  if(window.addEventListener) {
  window.addEventListener('load', function () {

 //check tool is pen or line or shape
  var chktool="pen";

   function init () {
    alert("Line3");
 // Find the canvas element.
 canvas = document.getElementById('canvas');
    context = canvas.getContext('2d');
//varblurup=10;
   context.shadowColor = 'colour';
   context.shadowBlur = 0;
   context.lineWidth=1;
    context.lineJoin = 'miter';
    context.miterLimit = 4;


this.context.save();
    // Pencil tool instance.
//tool = new tool_pencil();
  //alert("Pen");

 if(chktool=="pen")

 {    tool = new tool_pencil();
  alert("Pen");
 }else if (chktool=="line")
 {
     tool2 = new tool_line();
   alert("Line");
 }

    // Attach the mousedown, mousemove and mouseup event listeners.
    canvas.addEventListener('mousedown', ev_canvas, false);
    canvas.addEventListener('mousemove', ev_canvas, false);
    canvas.addEventListener('mouseup', ev_canvas, false);

  }

  // This painting tool works like a drawing pencil which tracks the mouse 
  // movements.
  function tool_pencil () {
    var tool = this;

    this.started = false;

    // This is called when you start holding down the mouse button.
 开发者_开发技巧   // This starts the pencil drawing.
    this.mousedown = function (ev) {
        context.beginPath();
        context.moveTo(ev._x, ev._y);
        tool.started = true;
    };

    // This function is called every time you move the mouse. Obviously, it only 
    // draws if the tool.started state is set to true (when you are holding down 
    // the mouse button).
    this.mousemove = function (ev) {

      if (tool.started) {
        context.lineTo(ev._x, ev._y);


 //this.style('stroke-opacity').value
    context.stroke();

      }


    };

    // This is called when you release the mouse button.
    this.mouseup = function (ev) {
      if (tool.started) {
        tool.mousemove(ev);
        tool.started = false;
      }
    };
  }

// The general-purpose event handler. This function just determines the mouse 
  // position relative to the canvas element.
  function ev_canvas (ev) {
    if (ev.layerX || ev.layerX == 0) { // Firefox
      ev._x = ev.layerX;
      ev._y = ev.layerY;
    } else if (ev.offsetX || ev.offsetX == 0) { // Opera
      ev._x = ev.offsetX;
      ev._y = ev.offsetY;
    }

    // Call the event handler of the tool.
    var func = tool[ev.type];
    if (func) {
      func(ev);
    }
  }

  init();

}, false); }

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I found the Mozilla canvas tutorial to be a helpful guide. It covers most areas including shape drawing:

https://developer.mozilla.org/en/Canvas_tutorial

https://developer.mozilla.org/en/Canvas_tutorial/Drawing_shapes

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It is quite an extended question so here are a couple of links about it..

HTML5 Canvas: Shape Drawing
A Quick Introduction to the HTML 5 Canvas
A Quick Introduction to the HTML 5 Canvas – Part Two