是 webglcontextcreationerror event同步触发还是异步触发?例如
canvas.addEventListener("webglcontextcreationerror", function() {
console.log("Error");
});
var context = canvas.getContext("webgl");
console.log("After creation");
在错误输出的情况下
"After creation"
"Error"
或
"Error"
"After creation"
?
我不确定如何强制这个事件自己找出答案。
最佳答案
所以有一个问题是您为什么要关心顺序? getContext
在失败时返回 null
所以如果你想知道它是否失败那么你就完成了。 webglcontextcreationerror
的唯一目的是让您了解失败的原因,因为 getContext
无法做到这一点。因此,您可以构建代码,使其无论是同步还是异步都无关紧要
var canvas = document.createElement('canvas')
function doSomethingWithStatusMessage(e) {
log("context creation error: "+ e.statusMessage);
}
canvas.addEventListener("webglcontextcreationerror", doSomethingWithStatusMessage);
log("2d: " + canvas.getContext('2d'));
log("webgl: " + canvas.getContext("webgl"));
log("after creation");
function log(msg, color) {
var div = document.createElement("pre");
div.appendChild(document.createTextNode(msg));
document.body.appendChild(div);
}
doSomethingWithStatus
消息可以做任何你想做的事。假设您基于 getContext
显示一个对话框。
if (!canvas.getContext("webgl")) {
g_dialog = new Dialog("can't create context", g_reason);
}
那么你可能会有这样的代码
var g_reason = "unknown";
var g_dialog;
function doSomethingWithStatusMessage(e) {
if (g_dialog) {
g_dialog.updateReason(e.statusMessage);
} else {
g_reason = g.statusMessage;
}
}
function Dialog(msg, reason) {
var div = document.createElement("div");
div.appendChild(document.createTextNode(msg));
var reasonNode = document.createTextNode("");
div.appendChild(reasonNode);
updateReason(reason);
function updateReason(reason) {
reasonNode.nodeValue = reason;
}
this.updateReason = updateReason;
}
var g_reason = "unknown";
var g_dialog;
function doSomethingWithStatusMessage(e) {
if (g_dialog) {
g_dialog.updateReason(e.statusMessage);
} else {
g_reason = e.statusMessage;
}
}
var canvas = document.createElement('canvas')
canvas.addEventListener("webglcontextcreationerror", doSomethingWithStatusMessage);
log("2d: " + canvas.getContext('2d'));
var gl = canvas.getContext("webgl");
log("webgl: " + gl);
log("after creation");
if (!gl) {
new Dialog("could not create WebGL context: ", g_reason);
}
function log(msg, color) {
var div = document.createElement("pre");
div.appendChild(document.createTextNode(msg));
document.body.appendChild(div);
}
function Dialog(msg, reason) {
var outer = document.createElement("div");
outer.className = "dialog";
var div = document.createElement("div");
div.appendChild(document.createTextNode(msg));
var reasonNode = document.createTextNode("");
div.appendChild(reasonNode);
outer.appendChild(div);
updateReason(reason);
document.body.appendChild(outer);
outer.addEventListener('click', close);
function updateReason(reason) {
reasonNode.nodeValue = reason;
}
function close() {
document.body.removeChild(outer);
outer.removeEventListener('click', close);
}
this.close = close;
this.updateReason = updateReason;
}
.dialog {
position: absolute;
z-index: 2;
background: rgba(0,0,0,0.8);
color: red;
left: 0;
top: 0;
width: 100%;
height: 100%;
display: flex;
justify-content: center;
align-content: center;
align-items: center;
}
例如,如果您想将错误报告给服务器,则只需稍后触发它,让异步消息有机会到达。
if (!canvas.getContext("webgl")) {
// give a moment for the async message to arrive
setTimeout(uploadReason, 1000);
}
剩下的就是
var g_reason = "unknown";
function doSomethingWithStatusMessage(e) {
g_reason = e.statusMessage;
}
function uploadReason() {
.. XHR g_reason to server ..
}
注:我file a bug on this part of the spec如果您愿意,可以跟进。
关于javascript - webglcontextcreationerror 事件 : is it triggered synchronously?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36565598/