HTML5 Canvas - Translation


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HTML5 canvas provides translate(x, y) method which is used to move the canvas and its origin to a different point in the grid.

Here argument x is the amount the canvas is moved to the left or right, and y is the amount it's moved up or down

Example

Following is a simple example which makes use of above method to draw various Spirographs −

<!DOCTYPE HTML>
<html>
   <head>
      
      <style>
         #test {
            width:100px;
            height:100px;
            margin:0px auto;
         }
      </style>
      
      <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');
               ctx.fillRect(0,0,300,300);
               
               for (i=0;i<3;i++) {
                  for (j=0;j<3;j++) {
                     ctx.save();
                     ctx.strokeStyle = "#FF0066";
                     
                     ctx.translate(50+j*100,50+i*100);
                     drawSpirograph(ctx,10*(j+3)/(j+2),-2*(i+3)/(i+1),10);
                     
                     ctx.restore();
                  }
               }
            }
            
            else {
               alert('You need Safari or Firefox 1.5+ to see this demo.');
            }
         }
         
         function drawSpirograph(ctx,R,r,O){
            var x1 = R-O;
            var y1 = 0;
            var i  = 1;
            
            ctx.beginPath();
            ctx.moveTo(x1,y1);
            
            do {
               if (i>20000) break;
               var x2 = (R+r)*Math.cos(i*Math.PI/72) - (r+O)*Math.cos(((R+r)/r)*(i*Math.PI/72))
               var y2 = (R+r)*Math.sin(i*Math.PI/72) - (r+O)*Math.sin(((R+r)/r)*(i*Math.PI/72))
               ctx.lineTo(x2,y2);
               
               x1 = x2;
               y1 = y2;
               i++;
            } while (x2 != R-O && y2 != 0 );
            ctx.stroke();
         }
      </script>
   </head>
   
   <body id="test" onload="drawShape();">
      <canvas id="mycanvas" width="400" height="400"></canvas>
   </body>
   
</html>

The above example would produce following result −


html5_canvas.htm

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