PHP DevLovers: Animate a Fill Circle using Canvas & JavaScript

Friday, December 27, 2013

Animate a Fill Circle using Canvas & JavaScript

The HTML5 <canvas> element is used to draw graphics, on the fly, via scripting (usually JavaScript).
The <canvas> element is only a container for graphics. You must use a script to actually draw the graphics.
Canvas has several methods for drawing paths, boxes, circles, text, and adding images.
However, the <canvas> element has no drawing abilities of its own (it is only a container for graphics) - you must use a script to actually draw the graphics.
The getContext() method returns an object that provides methods and properties for drawing on the canvas.

HTML CODE:

The markup looks like this:

<div id="container">

  <h1>html5 Canvas - Animate a Fill Circle using Canvas - by <a href="http://cathodesoft.com/">CathodeSoft</a></h1>

  <canvas id="Circle" width="578" height="200"></canvas>

</div>

JavaScript Code :

// Script by http://phpdevlovers.blogspot.in

// requestAnimationFrame Sping

var canvas = document.getElementById('Circle');

var context = canvas.getContext('2d');

var centerX = canvas.width / 2;

var centerY = canvas.height / 2;

var radius = 80;

var full = radius*2;

var amount = 0;

var amountToIncrease = 10;

function draw() {

context.save();

context.beginPath();

context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);

context.clip(); // Make a clipping region out of this path

// instead of filling the arc, we fill a variable-sized rectangle

// that is clipped to the arc

context.fillStyle = '#13a8a4';

// We want the rectangle to get progressively taller starting from the bottom

// There are two ways to do this:

// 1. Change the Y value and height every time

// 2. Using a negative height

// I'm lazy, so we're going with 2

context.fillRect(centerX - radius, centerY + radius, radius * 2, -amount);

context.restore(); // reset clipping region

context.beginPath();

context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);

context.lineWidth = 10;

context.strokeStyle = '#000000';

context.stroke();

// Every time, raise amount by some value:

amount += amountToIncrease;

if (amount > full) amount = 0; // restart

}

draw();

// Every second we'll fill more;

setInterval(draw, 1000);

</script>

DEMO url