Categories: CSSHTMLHTML 5 Notes For ProfessionalJavascript

Chapter 32: Canvas

Attribute	Description
height	Specifies the canvas height
width	Specifies the canvas width

Basic Example

The canvas element was introduced in HTML5 for drawing graphics.

<canvas id="myCanvas">
 Cannot display graphic. Canvas is not supported by your browser (IE<9)
</canvas>

The above will create a transparent HTML <canvas> element of 300×150 px in size.

You can use the canvas element to draw amazing stuff like shapes, graphs, manipulate images, create engaging
games etc. with JavaScript.

The canvas’s 2D drawable layer surface Object is referred to as CanvasRenderingContext2D; or from a
HTMLCanvasElement using the .getContext (“2d”) method:

var ctx = document.getElementById("myCanvas").getContext("2d");
// now we can refer to the canvas's 2D layer context using `ctx`
ctx.fillStyle = "#f00";
ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height); // x, y, width, height
ctx.fillStyle = "#000";
ctx.fillText("My red canvas with some black text", 24, 32); // text, x, y

jsFiddle example

Drawing two rectangles on a <canvas>

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="utf-8" />
 <title>Draw two rectangles on the canvas</title>
 <style>
 canvas{
 border:1px solid gray;
 }
 </style>
 <script async>
 window.onload = init; // call init() once the window is completely loaded
 function init(){
 // #1 - get reference to <canvas> element
 var canvas = document.querySelector('canvas');
 
 // #2 - get reference to the drawing context and drawing API
 var ctx = canvas.getContext('2d');
 // #3 - all fill operations are now in red
 ctx.fillStyle = 'red';GoalKicker.com – HTML5 Notes for Professionals 84
 // #4 - fill a 100x100 rectangle at x=0,y=0
 ctx.fillRect(0,0,100,100);
 
 // #5 - all fill operations are now in green
 ctx.fillStyle = 'green';
 
 // #6 - fill a 50x50 rectangle at x=25,y=25
 ctx.fillRect(25,25,50,50);
 
 }
 </script>
</head>
<body>
 <canvas width=300 height=200>Your browser does not support canvas.</canvas>
</body>
</html>