| <!DOCTYPE html> |
| <title>Layout Instability: layout shift when content expanded above the viewport</title> |
| <link rel="help" href="https://wicg.github.io/layout-instability/" /> |
| <script src="/resources/testharness.js"></script> |
| <script src="/resources/testharnessreport.js"></script> |
| <script src="resources/test-adapter.js"></script> |
| <script src="resources/util.js"></script> |
| <style> |
| body { |
| margin: 0; |
| /* To avoid browser automatic scroll offset adjustment for the expansion. */ |
| overflow-anchor: none; |
| } |
| </style> |
| <div id="expander" style="height: 50vh"></div> |
| <div id="shifted" style="width: 300px; height: 300vh; background: blue"></div> |
| <script> |
| |
| promise_test(async () => { |
| const watcher = new ScoreWatcher; |
| |
| // Wait for the initial render to complete. |
| await waitForAnimationFrames(2); |
| |
| const viewHeight = document.documentElement.clientHeight; |
| window.scrollTo(0, viewHeight); |
| |
| await waitForAnimationFrames(2); |
| |
| // Expander expands to push |shifted| down. |
| expander.style.height = '150vh'; |
| |
| const expectedScore1 = computeExpectedScore(300 * viewHeight, viewHeight); |
| |
| // Observer fires after the frame is painted. |
| cls_expect(watcher, {score: 0}); |
| await watcher.promise; |
| cls_expect(watcher, {score: expectedScore1}); |
| |
| // Expander expands to push |shifted| out of viewport. |
| expander.style.height = '200vh'; |
| |
| const expectedScore2 = expectedScore1 + |
| computeExpectedScore(0.5 * 300 * viewHeight, 0.5 * viewHeight); |
| await watcher.promise; |
| cls_expect(watcher, {score: expectedScore2}); |
| }, "Layout shift when content expanded above the viewport"); |
| |
| </script> |