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| 1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| 2 // Use of this source code is governed by a BSD-style license that can be |
| 3 // found in the LICENSE file. |
| 4 |
| 5 function busyLoop(millis) { |
| 6 for (var d = Date.now(); Date.now() - d < millis; ) { } |
| 7 } |
| 8 |
| 9 function visible() { |
| 10 if ("webkitVisibilityState" in document |
| 11 && document.webkitVisibilityState == "hidden") |
| 12 return false; |
| 13 if ("mozVisibilityState" in document |
| 14 && document.mozVisibilityState == "hidden") |
| 15 return false; |
| 16 if ("msVisibilityState" in document |
| 17 && document.msVisibilityState == "hidden") |
| 18 return false; |
| 19 return true; |
| 20 } |
| 21 |
| 22 var timerId = 0; |
| 23 function loop() { |
| 24 timerId = 0; |
| 25 if (!visible()) |
| 26 return; |
| 27 busyLoop(250); |
| 28 timerId = window.setTimeout(loop, 50); |
| 29 } |
| 30 |
| 31 function handler() { |
| 32 if (visible() && !timerId) |
| 33 timerId = window.setTimeout(loop, 50); |
| 34 } |
| 35 |
| 36 document.addEventListener("webkitvisibilitychange", handler, false); |
| 37 document.addEventListener("mozvisibilitychange", handler, false); |
| 38 document.addEventListener("msvisibilitychange", handler, false); |
| 39 |
| 40 loop(); |
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