HTML5 Canvas - Drawing Quadratic Curves


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There are following methods required to draw quadratic curve on the canvas:

SNMethod and Description
1

beginPath()

This method resets the current path.

2

moveTo(x, y)

This method creates a new subpath with the given point.

3

closePath()

This method marks the current subpath as closed, and starts a new subpath with a point the same as the start and end of the newly closed subpath.

4

fill()

This method fills the subpaths with the current fill style.

5

stroke()

This method strokes the subpaths with the current stroke style.

6

quadraticCurveTo(cpx, cpy, x, y)

This method adds the given point to the current path, connected to the previous one by a quadratic Bezier curve with the given control point.

The x and y parameters in quadraticCurveTo() method are the coordinates of the end point. cpx and cpy are the coordinates of the control point.

Example

Following is a simple example which makes use of above mentioned methods to draw a Quadratic curves.

<!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');

   // Draw shapes
    ctx.beginPath();
    ctx.moveTo(75,25);
    ctx.quadraticCurveTo(25,25,25,62.5);
    ctx.quadraticCurveTo(25,100,50,100);
    ctx.quadraticCurveTo(50,120,30,125);
    ctx.quadraticCurveTo(60,120,65,100);
    ctx.quadraticCurveTo(125,100,125,62.5);
    ctx.quadraticCurveTo(125,25,75,25);
    ctx.stroke();

  } else {
    alert('You need Safari or Firefox 1.5+ to see this demo.');
  }
}
</script>
</head>
<body onload="drawShape();">
   <canvas id="mycanvas"></canvas>
</body>
</html>

The above example would draw following shape:

Canvas Quadratic

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


html5_canvas.htm

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