Uderstanding HTML Canvas

Canvas is a new HTML element because its terminal figure suggests, it build a canvas on which a developer can paint anything.Canvas was initially introduced by Apple for use inside their own Mac OS X WebKit component in 2004.With the help of javascript users can draw in builds and deliver images on canvas.If javascript is disable in a browser even so, the canvas elemet will show its dawdle content(Content inside the tag instead of tag itself)
           Since the canvas gives developers an open arena to act with, it can quite useful to draw custom interfacesuch as game.
           The canvas tag has been supported since firefox 1.5, Chrome1.0, Opera 9.0, Safari 2. and IE 9.0

CANVAS TAG

         This is a Bare tag to display content.This tag just define width and hight..Here a simple examble to define canvas in an HTML document.

<canvas id="example" width="200" height="200">
This text is displayed if your browser does not support HTML5 Canvas.
</canvas>

Note:Default width 300 pixel height 150 pixel


Verfying canvas supprot

function isCanvasSupported(){
  var elem = document.createElement('canvas');
  return !!(elem.getContext && elem.getContext('2d'));
}

Draw Onto The Canvas With JavaScript

All drawing on the canvas must be done inside a JavaScript:

Example

<script>
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="#FF0000";
ctx.fillRect(0,0,150,75);
</script> 

Example explained:
First, find the <canvas> element:

var c=document.getElementById("myCanvas"); 

Then, call its getContext() method (you must pass the string "2d" to the getContext() method):

var ctx=c.getContext("2d");

 

The getContext("2d") object is a built-in HTML5 object, with many properties and methods for drawing paths, boxes, circles, text, images, and more.
The next two lines draws a red rectangle:

ctx.fillStyle="#FF0000";
ctx.fillRect(0,0,150,75); 

The fillStyle property can be a CSS color, a gradient, or a pattern. The default fillStyle is #000000 (black).
The fillRect(x,y,width,height) method draws a rectangle filled with the current fill style.

Canvas - Text

To draw text on a canvas, the most important property and methods are:

• font - defines the font properties for text
• fillText(text,x,y) - Draws "filled" text on the canvas
• strokeText(text,x,y) - Draws text on the canvas (no fill)

Using fillText():

Example

Write a 30px high filled text on the canvas, using the font "Arial":
JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.font="30px Arial";
ctx.fillText("Hello World",10,50);

Try it yourself »

Using strokeText():

Example

Write a 30px high text (no fill) on the canvas, using the font "Arial":
JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.font="30px Arial";
ctx.strokeText("Hello World",10,50);

Try it yourself »

---

Canvas - Gradients

Gradients can be used to fill rectangles, circles, lines, text, etc. Shapes on the canvas are not limited to solid colors.
There are two different types of gradients:

• createLinearGradient(x,y,x1,y1) - Creates a linear gradient
• createRadialGradient(x,y,r,x1,y1,r1) - Creates a radial/circular gradient

Once we have a gradient object, we must add two or more color stops.
The addColorStop() method specifies the color stops, and its position along the gradient. Gradient positions can be anywhere between 0 to 1.
To use the gradient, set the fillStyle or strokeStyle property to the gradient, and then draw the shape, like a rectangle, text, or a line.
Using createLinearGradient():

Example

Create a linear gradient. Fill rectangle with the gradient:
JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");

// Create gradient
var grd=ctx.createLinearGradient(0,0,200,0);
grd.addColorStop(0,"red");
grd.addColorStop(1,"white");

// Fill with gradient
ctx.fillStyle=grd;
ctx.fillRect(10,10,150,80);

Try it yourself »

Using createRadialGradient():

Example

Create a radial/circular gradient. Fill rectangle with the gradient:
JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");

// Create gradient
var grd=ctx.createRadialGradient(75,50,5,90,60,100);
grd.addColorStop(0,"red");
grd.addColorStop(1,"white");

// Fill with gradient
ctx.fillStyle=grd;
ctx.fillRect(10,10,150,80);

Try it yourself »

---

Canvas - Images

To draw an image on a canvas, we will use the following method:

• drawImage(image,x,y)

Image to use:

Example

Draw the image onto the canvas:
JavaScript:

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var img=document.getElementById("scream");
ctx.drawImage(img,10,10);

Try it yourself »

 NOTE: This article is Copied from 

http://www.w3schools.com/html/html5_canvas.asp

You can visit this page for further detailes 

A detailed tutorial about html canvas 5 will post later

 
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