tor-browser

The Tor Browser
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helper_custom_scrolling_bug1932985.html (3086B)

      1 <!DOCTYPE HTML>
      2 <meta charset="utf-8">
      3 <meta name="viewport" content="width=device-width, minimum-scale=1.0">
      4 <title>Test that a custom scrolling implementation using scrollBy() is
      5       not much slower than native wheel event handling</title>
      6 <script src="apz_test_utils.js"></script>
      7 <script src="apz_test_native_event_utils.js"></script>
      8 <script src="/tests/SimpleTest/paint_listener.js"></script>
      9 <style>
     10  html {
     11    scroll-behavior: smooth;
     12  }
     13  .spacer {
     14    height: 2000vh;
     15  }
     16 </style>
     17 <div class="spacer"></div>
     18 <script>
     19  async function test() {
     20    // The test will be sending 10 events and expecting each to
     21    // accomplish a full 50 pixels of scrolling.
     22    let wheelDelta = 50;
     23    let eventCount = 10;
     24    let finalDestination = eventCount * wheelDelta;
     25 
     26    // Set up a custom scrolling mechanism which emulates the one in
     27    // arrowscrollbox.js in important respects:
     28    //   - Listen for wheel events but preventDefault() them and scroll
     29    //     using scrollBy() instead.
     30    //   - Track the scroll destination in script.
     31    //   - Reset the destination when a `scrollend` is received.
     32    let currentDestination = 0;
     33    let isScrolling = false;
     34    window.addEventListener("wheel", e => {
     35      if (!isScrolling) {
     36        currentDestination = window.scrollY;
     37        isScrolling = true;
     38      }
     39      currentDestination += wheelDelta;
     40      let delta = currentDestination - window.scrollY;
     41      window.scrollBy(0, delta);
     42      e.preventDefault();
     43    }, { passive: false });
     44    window.addEventListener("scrollend", () => {
     45      isScrolling = false;
     46    });
     47 
     48    // Make sure APZ is aware of the active event listener.
     49    await promiseApzFlushedRepaints();
     50 
     51    // Set up a promise that is resolved when we reach the expected
     52    // destination.
     53    let destinationPromise = new Promise(resolve => {
     54      window.addEventListener("scroll", () => {
     55        info(`Scrolled to ${window.scrollY}`);
     56        // Use fuzzy comparison with epsilon=1 to account for rounding
     57        // of scrollBy() delta to the nearest pixel. This should be fixed
     58        // by bug 1674687.
     59        if (window.scrollY >= (finalDestination - 1)) {
     60          ok(true, "Scroll destination reached");
     61          resolve();
     62        }
     63      });
     64    });
     65 
     66    // Send 10 wheel events in fairly quick succession (one frame between each).
     67    let useTouchpad = (location.search == "?touchpad");
     68    for (var i = 0; i < eventCount; i++) {
     69      if (useTouchpad) {
     70        let phase;
     71        if (i == 0) {
     72          phase = NativePanHandler.beginPhase;
     73        } else if (i == (eventCount - 1)) {
     74          phase = NativePanHandler.endPhase;
     75        } else {
     76          phase = NativePanHandler.updatePhase;
     77        }
     78        await NativePanHandler.promiseNativePanEvent(window, 50, 50, 0, -50, phase);
     79      } else {
     80        await synthesizeNativeWheel(window, 50, 50, 0, -50);
     81      }
     82      await promiseFrame();
     83    }
     84 
     85    // Wait for us to reach the destination.
     86    await destinationPromise;
     87  }
     88 
     89  waitUntilApzStable()
     90  .then(test)
     91  .then(subtestDone, subtestFailed);
     92 </script>