Add a test for fullscreen for the A/B/A case

See the discussion at [1] for more context. This test requests fullscreen on A, then B, then A, where A and B are sibling divs. All three requests should succeed, and at the end, A should be topmost (and the fullscreen element) with both A and B in the top layer. [1] whatwg/fullscreen#223 Change-Id: I3f35dda5b9eb1bc24201616bb5bb4949d20fd170 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4501251 Commit-Queue: Mason Freed <[email protected]> Reviewed-by: Joey Arhar <[email protected]> Auto-Submit: Mason Freed <[email protected]> Cr-Commit-Position: refs/heads/main@{#1141456}
web-platform-tests · May 9, 2023 · bf4540b · bf4540b
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diff --git a/fullscreen/api/fullscreen-reordering.html b/fullscreen/api/fullscreen-reordering.html
@@ -0,0 +1,62 @@
+<!DOCTYPE html>
+<title>Re-requesting fullscreen doesn't fail but doesn't change order</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="../../html/semantics/popovers/resources/popover-utils.js"></script>
+
+<div class="elements">
+  <div id="A">Element A</div>
+  <div id="B">Element B</div>
+</div>
+
+<style>
+  .elements>div {
+    width:200px;
+    height:200px;
+  }
+  #A { background: blue; }
+  #B { background: green; }
+</style>
+
+<script>
+promise_test(async (t) => {
+  t.add_cleanup(async () => {
+    while (document.fullscreenElement)
+      await document.exitFullscreen();
+  });
+  document.onfullscreenerror = () => assert_unreached('fullscreenerror should not happen');
+  const A = document.getElementById('A');
+  const B = document.getElementById('B');
+  assert_true(!isTopLayer(A) && !isTopLayer(B));
+  await blessTopLayer(document.body);
+  await A.requestFullscreen();
+  assert_equals(document.fullscreenElement,A,'first A request');
+  assert_true(isTopLayer(A),'A top layer');
+  await blessTopLayer(A);
+  try {
+    await B.requestFullscreen();
+  } catch (error) {
+    assert_unreached('The second call to requestFullscreen rejected - it should be possible to put siblings into fullscreen together');
+  }
+  assert_equals(document.fullscreenElement,B,'B request');
+  assert_true(isTopLayer(B),'B top layer');
+  assert_true(isTopLayer(A),'A still top layer');
+  await blessTopLayer(B);
+  await A.requestFullscreen();
+  assert_true(isTopLayer(A),'A is still top layer');
+  assert_true(isTopLayer(B),'B is still top layer');
+  assert_equals(document.fullscreenElement,A,'A is moved back to the top of the top layer stack');
+  assert_equals(document.elementFromPoint(10,10),A,'A should be topmost');
+
+  await document.exitFullscreen();
+  assert_equals(document.fullscreenElement,B,'B goes back to being the fullscreen element');
+  assert_true(isTopLayer(B),'B is still top layer');
+  assert_false(isTopLayer(A),'A is no longer top layer');
+  await document.exitFullscreen();
+  assert_equals(document.fullscreenElement,null,'Both closed');
+  assert_false(isTopLayer(A),'A is no longer top layer');
+  assert_false(isTopLayer(B),'B is no longer top layer');
+}, 'Requesting fullscreen on A, then B, then A');
+</script>
diff --git a/html/semantics/popovers/resources/popover-utils.js b/html/semantics/popovers/resources/popover-utils.js
@@ -47,6 +47,22 @@ async function sendEnter() {
 function isElementVisible(el) {
   return !!(el.offsetWidth || el.offsetHeight || el.getClientRects().length);
 }
+function isTopLayer(el) {
+  // A bit of a hack. Just test a few properties of the ::backdrop pseudo
+  // element that change when in the top layer.
+  const properties = ['right','background'];
+  const testEl = document.createElement('div');
+  document.body.appendChild(testEl);
+  const computedStyle = getComputedStyle(testEl, '::backdrop');
+  const nonTopLayerValues = properties.map(p => computedStyle[p]);
+  testEl.remove();
+  for(let i=0;i<properties.length;++i) {
+    if (getComputedStyle(el,'::backdrop')[properties[i]] !== nonTopLayerValues[i]) {
+      return true;
+    }
+  }
+  return false;
+}
 async function finishAnimations(popover) {
   popover.getAnimations({subtree: true}).forEach(animation => animation.finish());
   await waitForRender();