simon.fraser@apple.com | 61d3e78 | 2014-12-06 01:25:21 +0000 | [diff] [blame] | 1 | <!DOCTYPE html> |
| 2 | <head> |
| 3 | <style> |
| 4 | #testInner { |
| 5 | position: absolute; |
| 6 | width: 600px; |
| 7 | top: 400px; |
| 8 | left: 200px;; |
| 9 | padding: 1em; |
| 10 | background: yellow; |
| 11 | box-shadow: 0 0 0.5em gray; |
| 12 | } |
| 13 | |
| 14 | .marker { |
| 15 | position: fixed; |
| 16 | background: black; |
| 17 | color: white; |
| 18 | top: 200px; |
| 19 | padding: 1em; |
| 20 | } |
| 21 | |
| 22 | .spacer { |
| 23 | height: 200px; |
| 24 | } |
| 25 | |
| 26 | button { |
| 27 | position: fixed; |
| 28 | top: 100px; |
| 29 | left: 200px; |
| 30 | padding: 2em; |
| 31 | font-size: 16px; |
| 32 | font-weight: bold; |
| 33 | } |
| 34 | |
| 35 | .trigger #testInner { |
| 36 | -webkit-transform: translateY(-200px); |
| 37 | } |
| 38 | </style> |
| 39 | </head> |
| 40 | <body> |
| 41 | <button onclick="toggleRunning()"> |
| 42 | CLICK ME to start / stop test |
| 43 | </button> |
| 44 | <div class="marker">Correct top position</div> |
| 45 | <div id="parent" class="trigger"> |
| 46 | <div id="testInner">test element</div> |
| 47 | </div> |
| 48 | <p class="spacer">.</p> |
| 49 | <p class="spacer">.</p> |
| 50 | <p class="spacer">.</p> |
| 51 | <p class="spacer">.</p> |
| 52 | <p class="spacer">.</p> |
| 53 | <p class="spacer">.</p> |
| 54 | <p class="spacer" id="last">.</p> |
| 55 | |
| 56 | <script> |
| 57 | var INTERVAL_MS = 17; |
| 58 | var testElement = document.getElementById('testInner'); |
| 59 | var testContainerElement = document.getElementById('parent'); |
| 60 | |
| 61 | var state = {}; |
| 62 | state.triggerTranslationOnOrOff = false; |
| 63 | state.running = false; |
| 64 | state.intervalId = 0; |
| 65 | |
| 66 | function updateState() |
| 67 | { |
| 68 | var translated = testContainerElement.classList.contains('trigger'); |
| 69 | state.scrolled = !translated; |
| 70 | } |
| 71 | |
| 72 | function toggleRunning() |
| 73 | { |
| 74 | state.running = !state.running; |
| 75 | if (state.running) { |
| 76 | updateState(); |
| 77 | state.intervalId = setInterval(runSequence, INTERVAL_MS); |
| 78 | } else { |
| 79 | clearInterval(state.intervalId); |
| 80 | } |
| 81 | } |
| 82 | |
| 83 | function doExpensiveContentUpdate() |
| 84 | { |
| 85 | var content = 'I should be stable at the correct position and not flicker above/below'; |
| 86 | if (state.scrolled) |
| 87 | content += '.'; |
| 88 | |
| 89 | testElement.innerHTML = content; |
| 90 | |
| 91 | var lastElement = document.getElementById('last'); |
| 92 | var startTime = Date.now(); |
| 93 | for (var i = 0; i < 1000; i++) { |
| 94 | lastElement.innerHTML = (lastElement.innerHTML + '.'); |
| 95 | } |
| 96 | var domWriteTimeMs = Date.now() - startTime; |
| 97 | if (domWriteTimeMs > 2 * INTERVAL_MS) |
| 98 | lastElement.innerHTML = ''; |
| 99 | } |
| 100 | |
| 101 | function runSequence() |
| 102 | { |
| 103 | doExpensiveContentUpdate(); |
| 104 | |
| 105 | var newScrollTop; |
| 106 | if (state.scrolled) { |
| 107 | testContainerElement.classList.add('trigger'); |
| 108 | newScrollTop = 0; |
| 109 | } else { |
| 110 | testContainerElement.classList.remove('trigger'); |
| 111 | newScrollTop = 200; |
| 112 | } |
| 113 | |
| 114 | document.body.scrollTop = newScrollTop; |
| 115 | state.scrolled = !state.scrolled; |
| 116 | } |
| 117 | |
| 118 | </script> |
| 119 | </body> |
| 120 | |