html - Preventing Canvas Clear when Resizing Window

Question

I'm trying to create a simple app that draws rectangles within the Canvas tag. I've got the Canvas resizing to fullscreen, but whenever I resize the viewport, Canvas clears. I'm trying to prevent it from clearing and just keeping the content thats within it. Any ideas?

http://mediajux.com/experiments/canvas/drawing/

Thanks!

      /*
      * This is the primary class used for the application
      * @author Alvin Crespo
      */
      var app = (function(){

        var domBod          = document.body;
        var canvas          = null;
        var canvasWidth     = null;
        var canvasHeight     = null;

        return {

          //Runs after the DOM has achieved an onreadystatechange of "complete"
          initApplication: function()
          {
            //setup envrionment variables
            canvas = document.getElementById('canvas') || null;

            //we need to resize the canvas at the start of the app to be the full window
            this.windowResized();

            //only set the canvas height and width if it is not false/null
            if(canvas)
            {
              canvasWidth = canvas.offsetWidth;
              canvasHeight = canvas.offsetHeight;        
            }

            //add window events
            window.onresize = this.windowResized;   

            circles.canvas = canvas;
            circles.canvasWidth = canvasWidth;
            circles.canvasHeight = canvasHeight;
            circles.generateCircles(10);  

            setInterval(function(){
                circles.animateCircles();
            }, 50);   
          },

          /**
          * Executes Resizing procedures on the canvas element
          */
          windowResized: function()
          {
            (this.domBod === null) ? 'true' : 'false';
            try{
              console.log(canvas);
              canvas.setAttribute('width', document.body.clientWidth);
              canvas.setAttribute('height', document.body.clientHeight);        
            }catch(e) {
              console.log(e.name + " :: " + e.message);
            }
          },

          /**
          * Returns the canvas element 
          * @returns canvas
          */
          getCanvas: function()
          {
            return canvas;
          }

        };
      })();

Answer 1

Setting the canvas width attribute will clear the canvas. If you resize the style width (e.g. canvas.style.visibility), it will scale (usually not in such a pretty way). If you want to make the canvas bigger but keep the elements in it as they are, i would suggest storing the canvas as an image -- e.g. call the toDataURL method to get the image, then draw that to the resized canvas with drawImage().