gistfile1.js

    resizeCanvas = function (largerOrSmaller){
      scaleValue = (largerOrSmaller == "larger") ? 0.1 : -0.1
      $('#canvasHolder').css({ scale: ($('#canvasHolder').css('scale') + scaleValue) });

      offset = $("#canvasHolder").offset()
      if (largerOrSmaller == "larger")
        if (offset.top > 0 && offset.left > 0)
          resizeCanvas("larger")
        else
          $('#canvasHolder').css({ scale: ($('#canvasHolder').css('scale') - scaleValue) });
      else
        if (offset.top < 0 || offset.left < 0)
          resizeCanvas("smaller")
        else
          $('#canvasHolder').css({ scale: ($('#canvasHolder').css('scale') - scaleValue) });
    }

    fitCanvas = function() {
      $('#canvasHolder').css({
       position:'absolute',
       left: ($(window).width() - $('#canvasHolder').outerWidth())/2,
       top: ($(window).height() - $('#canvasHolder').outerHeight())/2
      });
      offset = $("#canvasHolder").offset()
      if (offset.top < 0 || offset.left < 0)
        resizeCanvas("smaller")
      else
        resizeCanvas("larger")
    }

    $(window).resize(function(){
      fitCanvas()
    });
    fitCanvas()