HTML5 Canvas - Drawing Quadratic Curves


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We require the following methods to draw quadratic curves on the canvas −

S.No. Method 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.

Live Demo
<!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');
               
               // 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 id = "test" onload = "drawShape();">
      <canvas id = "mycanvas"></canvas>
   </body>
   
</html>

The above example would draw the following shape −


html5_canvas.htm

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