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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>
<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 onload="drawShape();">
   <canvas id="mycanvas" width="400" height="400"></canvas>
</body>
</html>

The above example would produce following result:

Canvas Translation

To learn above concept - Do Online Practice using latest version of either Safari or Opera.


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