HTML5 Canvas - Transforms


Advertisements


HTML5 canvas provides methods which 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.

Sr.No. Method and Description
1 transform(m11, m12, m21, m22, dx, dy)

This method changes the transformation matrix to apply the matrix given by the arguments.

2 setTransform(m11, m12, m21, m22, dx, dy)

This method changes the transformation matrix to the matrix given by the arguments .

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.

Example

Following is a simple example which makes use of transform() and setTransform() methods −

<!DOCTYPE HTML>
<html>
   <head>
      
      <script type="text/javascript">
         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>

The above example would produce following result −


html5_canvas.htm

Advertisements