帮助我了解谷歌地图如何显示图像?

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然后,他们使用“onload”和“onerror”事件来检测图像是否正确加载。

如果图像超时,他们会重试下载。这是通过设置一个计时器来实现的,一旦计时器过期,就重新设置映像的src属性。

var tile = document.createElement('img');
var url = 'http://sometilehost/X.Y.Z.png';
var downloadTimeout = 10000;    // Retry in 10 seconds

// Tile downloaded successfully
tile.onload = function (e) {
    window.clearTimeout(tile.downloadTimer);
    alert('tile downloaded');
};
// The tile couldn't be downloaded. 404, 503 ...
tile.onerror = function (e) {
    window.clearTimeout(tile.downloadTimer);
    alert('tile not downloaded');
};
// This will fire if the tile doesn't download in time
tile.downloadTimer = window.setTimeout(function () {
    tile.src = url; // Start the download again
}, downloadTimeout);
tile.src = url;