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How the Canvas Javascript API works in major browsers

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2023-09-16 08:53:021454browse

Canvas Javascript API 在主要浏览器中的作用

The canvas JavaScript API is a powerful tool for creating and manipulating graphics on the web. It allows you to draw 2D graphics using JavaScript code and is supported by most modern web browsers. Game operations, animation, video processing, and more all come from the Canvas API.

The canvas API is implemented in the form of canvas element, which is an HTML element that can be placed in an HTML document. The canvas element serves as a drawing surface and can be styled and positioned using CSS.

To draw graphics on the canvas, you can use the canvas API's drawing methods, such as arc, lineTo, and fillRect. These methods allow you to draw shapes, lines, and other graphics on the canvas.

Browser support for Canvas API

Google Chrome and Mozilla Firefox are the main browsers that support canvas API. Never use Safari or Microsoft Edge with the Canvas API. The canvas API is supported by all major browsers except Internet Explorer.

Canvas is available for Windows, Linux, Mac, Android and iOS and all major browsers. The operating system should perform all security checks and upgrades to ensure the canvas API works properly. Here is a list of such browsers and their versions.

  • Chrome

  • Firefox, but extension version is not supported

  • edge

  • Respondus Lockdown browsers only support the latest system requirements.

  • Safari only for Macintosh

Systems with at least 1GB of RAM are suitable for using the canvas API. Native mobile browsers have less support for tablet devices. The default Android browser changes depending on the mobile device.

Mobile browser

iOS

Safari is the default browser and has limited support for Canvas.

Chrome

Photon Flash Player supports Flash

Android

  • Chrome is the default browser and has limited support for Canvas

  • Firefox browser

Screen Reader

  • Macintosh VoiceOver in the latest version of Safari

  • JAWS for PC in the latest version of Firefox

  • PC NNVDA (latest version of Firefox)

Chrome does not support screen readers in canvas.

Detect Canvas API browser supported code

Canvas is an HTML 5 element. The getContext() method in canvas returns the drawing context. If null is returned, it means that the canvas element is not supported.

Users can follow the syntax below and use the code below to check whether the browser supports the canvas element.

grammar

if(document.createElement('canvas').getContext){
   /*Canvas object available*/
}

The if condition in the syntax creates a canvas element and attempts to get the context. If the context is returned, the browser supports canvas.

Example

In this program, users can check browser support for canvas by clicking a button. When you click the button, the event calls a function that tries to get the canvas context using the above syntax. There is a flag variable in the program that distinguishes browser support and displays a message to the user. 

<html>
<body>
   <h2> Check if your browser support canvas API in JavScript </i>
   </h2>
   <button class="button" onclick="browserSupport()">
      Check
   </button>
   <br> <br>
   <b class="outputEl"> </b>
   <script>
      function browserSupport() {
         if (document.createElement('canvas').getContext)
            hasSupport = true;
         else
            hasSupport = false;
         document.querySelector('.outputEl').innerHTML = hasSupport ? "Browser supports canvas" : "Browser does not support canvas";
      }
   </script>
</body>
</html>

Example

Here is an example of how to draw a simple circle on a canvas using the canvas API -

<html>
<body>
   <p> Drawing a circle using Canvas JavaScript API </p>
   <canvas id="myCanvas" width="200" height="100"></canvas>
   <script>
      var canvas = document.getElementById("myCanvas");
      var context = canvas.getContext("2d");
      context.beginPath();
      context.arc(95, 50, 40, 0, 2 * Math.PI);
      context.stroke();
   </script>
</body>
<html>

In this example, the created canvas element has an id of "myCanvas" and a width and height of 200 and 100 pixels respectively. The getContext method is used to obtain the drawing context of the canvas, and the arc method is used to draw a circle with a center point of (95, 50) and a radius of 40 pixels. Then use the stroke method to draw the circle on the canvas.

This tutorial helps us understand whether Canvas API is a built-in native part of all major browsers. Not all major browsers have a built-in canvas API. We now know a piece of code to detect browser support for the canvas API. Users can avoid errors when coding canvases using previous browsers, supported by this code snippet for checking.

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