HTML Canvas

From WikiOD

Parameters[edit | edit source]

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

Remarks[edit | edit source]

  • This tag is not compatible with versions of Internet Explorer less than 9. Check for browser compatibility.
  • canvas is only a container for graphics, and the actual drawing of graphics is done by JavaScript.

Basic Example[edit | edit source]

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)

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

<!DOCTYPE html>
<html lang="en">
    <meta charset="utf-8" />
    <title>Draw two rectangles on the canvas</title>
          border:1px solid gray;
    <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'; 

        // #4 - fill a 100x100 rectangle at x=0,y=0

        // #5 - all fill operations are now in green
        ctx.fillStyle = 'green'; 

        // #6 - fill a 50x50 rectangle at x=25,y=25

  <canvas width=300 height=200>Your browser does not support canvas.</canvas>

This example looks like this: