问题
I am attempting to detect WebGL support across multiple browsers and I've encountered the following scenario. The current version of Firefox appears to report positive support using the following check, even when the visitor's video card is black-listed and/or WebGL is disabled:
if (window.WebGLRenderingContext) {
// This is true in Firefox under certain circumstances,
// even when WebGL is disabled...
}
I've tried instructing my users to enable WebGL using the following steps. This has worked in some cases, but not always. Obviously, this is not something I can request of the general public:
- Type about:config in Firefox’s address bar
- To enable WebGL, set webgl.force-enabled to true
This has led me to create my own method for detecting support, which uses jQuery to inject a canvas element to detect support. This pulls on a number of techniques I found in various WebGL libraries and plugins. The trouble is, it is extremely difficult to test (any comments on whether the link below works for you are much appreciated!). To make this an objective question, I would like to know if there's a universally accepted way to detect WebGL support across all browsers.
TEST URL:
http://jsfiddle.net/Jn49q/5/
回答1:
[Oct 2014] I've updated modernizrs example to match their current implementation, which is a cleaned up version from http://get.webgl.org/ further below.
Modernizr does,
var canvas;
var ctx;
var exts;
try {
canvas = createElement('canvas');
ctx = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');
exts = ctx.getSupportedExtensions();
}
catch (e) {
return;
}
if (ctx !== undefined) {
Modernizr.webglextensions = new Boolean(true);
}
for (var i = -1, len = exts.length; ++i < len; ){
Modernizr.webglextensions[exts[i]] = true;
}
canvas = undefined;
Chromium points to http://get.webgl.org/ for the canonical support implementation,
try { gl = canvas.getContext("webgl"); }
catch (x) { gl = null; }
if (gl == null) {
try { gl = canvas.getContext("experimental-webgl"); experimental = true; }
catch (x) { gl = null; }
}
回答2:
The excellent Three library has, in fact, a mechanism for detecting the following:
- WebGL support
- File API support
- Workers support
For WebGL, particularly, here is the code that is used:
function webgl_support () {
try {
var canvas = document.createElement('canvas');
return !!window.WebGLRenderingContext &&
(canvas.getContext('webgl') || canvas.getContext('experimental-webgl'));
} catch(e) {
return false;
}
};
That code snippet is part of a Detector class which may also display the corresponding error messages to the user.
回答3:
As seen in http://www.browserleaks.com/webgl#howto-detect-webgl
This is a proper javascript function to detect WebGL support, with all kind of experimental WebGL context names and with checking of special cases, such as blocking WebGL functions by NoScript or TorBrowser.
It will report one of the three WebGL capability states:
- WebGL is enabled — return TRUE, or return
- WebGL object, if the first argument was passed
- WebGL is disabled — return FALSE, you can change it if you need>
- WebGL is not implimented — return FALSE
function webgl_detect(return_context)
{
if (!!window.WebGLRenderingContext) {
var canvas = document.createElement("canvas"),
names = ["webgl2", "webgl", "experimental-webgl", "moz-webgl", "webkit-3d"],
context = false;
for(var i=0;i< names.length;i++) {
try {
context = canvas.getContext(names[i]);
if (context && typeof context.getParameter == "function") {
// WebGL is enabled
if (return_context) {
// return WebGL object if the function's argument is present
return {name:names[i], gl:context};
}
// else, return just true
return true;
}
} catch(e) {}
}
// WebGL is supported, but disabled
return false;
}
// WebGL not supported
return false;
}
回答4:
In addition to @Andrew answer, there is also experimental mode which can be supported. I have written following snippet of code:
var canvasID = 'webgl',
canvas = document.getElementById(canvasID),
gl,
glExperimental = false;
function hasWebGL() {
try { gl = canvas.getContext("webgl"); }
catch (x) { gl = null; }
if (gl === null) {
try { gl = canvas.getContext("experimental-webgl"); glExperimental = true; }
catch (x) { gl = null; }
}
if(gl) { return true; }
else if ("WebGLRenderingContext" in window) { return true; } // not a best way, as you're not 100% sure, so you can change it to false
else { return false; }
}
Change canvasID variable according to your ID.
Tested on Chrome, Safari, Firefox, Opera and IEs (8 to 10). In case of Safari remember that it's available, but you need to enable WebGL explicitly (enable the developer menu and enable Web GL option after).
回答5:
In order to detect browsers that support WebGL, but leaving out older browsers with may not support it well (as needed in WebGL detected as supported when it is actually not for ruling out Android 4.4.2 devices), I am adding a tighter, though unrelated check:
function hasWebGL() {
var supported;
try {
var canvas = document.createElement('canvas');
supported = !! window.WebGLRenderingContext && (canvas.getContext('webgl') || canvas.getContext('experimental-webgl'));
} catch(e) { supported = false; }
try {
// let is by no means required, but will help us rule out some old browsers/devices with potentially buggy implementations: http://caniuse.com/#feat=let
eval('let foo = 123;');
} catch (e) { supported = false; }
if (supported === false) {
console.log("WebGL is not supported");
}
canvas = undefined;
return supported;
},
回答6:
// this code will detect WebGL version until WebGL Version maxVersionTest
var
maxVersionTest = 5,
canvas = document.createElement('canvas'),
webglVersion = (canvas.getContext('webgl') || canvas.getContext('experimental-webgl')) ? 1 : null,
canvas = null; // free context
// range: if maxVersionTest = 5 makes [5, 4, 3, 2]
Array.apply(null, Array(maxVersionTest - 1))
.map(function (_, idx) {return idx + 2;})
.reverse()
.some(function(version){
// cant reuse canvas, potential to exceed contexts or mem limit *
if (document.createElement('canvas').getContext('webgl'+version))
return !!(webglVersion = version);
});
console.log(webglVersion);
* re "potential to exceed contexts or mem limit" see https://bugs.chromium.org/p/chromium/issues/detail?id=226868
回答7:
From MDN:
// Run everything inside window load event handler, to make sure
// DOM is fully loaded and styled before trying to manipulate it.
window.addEventListener("load", function() {
var paragraph = document.querySelector("p"),
button = document.querySelector("button");
// Adding click event handler to button.
button.addEventListener("click", detectWebGLContext, false);
function detectWebGLContext () {
// Create canvas element. The canvas is not added to the
// document itself, so it is never displayed in the
// browser window.
var canvas = document.createElement("canvas");
// Get WebGLRenderingContext from canvas element.
var gl = canvas.getContext("webgl")
|| canvas.getContext("experimental-webgl");
// Report the result.
if (gl && gl instanceof WebGLRenderingContext) {
paragraph.innerHTML =
"Congratulations! Your browser supports WebGL.";
} else {
paragraph.innerHTML = "Failed to get WebGL context. "
+ "Your browser or device may not support WebGL.";
}
}
}, false);body {
text-align : center;
}
button {
display : block;
font-size : inherit;
margin : auto;
padding : 0.6em;
}<p>[ Here would go the result of WebGL feature detection ]</p>
<button>Press here to detect WebGLRenderingContext</button>来源：https://stackoverflow.com/questions/11871077/proper-way-to-detect-webgl-support