HTML5 Canvas Transformation Matrix

Javascript Web Development Front End Scripts

HTML5 canvas provides methods that allow modifications directly to the transformation matrix. The transformation matrix must initially be the identity transform. It may then be adjusted using the transformation methods.

The transform (m11, m12, m21, m22, dx, dy) method must multiply the current transformation matrix with the matrix described by −

m11 m21 dx
m12 m22 dy
 0   0  1

The setTransform(m11, m12, m21, m22, dx, dy) method must reset the current transform to the identity matrix, and then invoke the transform(m11, m12, m21, m22, dx, dy) method with the same arguments.

<!DOCTYPE HTML>
<html>
   <head>
      <script>
         function drawShape(){

            // get the canvas element using the DOM
            var canvas = document.getElementById('mycanvas');

            // Make sure we don't execute when canvas isn't supported
            if (canvas.getContext){

               // use getContext to use the canvas for drawing
               var ctx = canvas.getContext('2d');
               var sin = Math.sin(Math.PI/6);
               var cos = Math.cos(Math.PI/6);
               ctx.translate(200, 200);
               var c = 0;

               for (var i=0; i <= 12; i++) {
                  c = Math.floor(255 / 12 * i);
                  ctx.fillStyle = "rgb(" + c + "," + c + "," + c + ")";
                  ctx.fillRect(0, 0, 100, 100);
                  ctx.transform(cos, sin, -sin, cos, 0, 0);
               }
               ctx.setTransform(-1, 0, 0, 1, 200, 200);
               ctx.fillStyle = "rgba(100, 100, 255, 0.5)";
               ctx.fillRect(50, 50, 100, 100);
            } else {
               alert('You need Safari or Firefox 1.5+ to see this demo.');
            }
         }
      </script>
   </head>
   <body onload="drawShape();">
      <canvas id = "mycanvas" width = "400" height = "400"></canvas>
   </body>
</html>