[css-scroll-snap] Adopt focused, targeted, block priority order

As agreed to in a recent spec issue[1], when re-snapping after a layout change, if it is not possible to follow the selected targets in both axes, we should select an axis to follow. Priority should be given among axes according to: 1. the axis with a focused area, if any, 2. the axis with a targeted [2] area, if any, 3. the block axis. [1]w3c/csswg-drafts#9622 (comment) [2]https://drafts.csswg.org/selectors/#the-target-pseudo Bug: 329250094 Change-Id: Idef6ddbbe0f613ec32f220c89848ea809fd10922 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5444525 Reviewed-by: Steve Kobes <[email protected]> Commit-Queue: David Awogbemila <[email protected]> Cr-Commit-Position: refs/heads/main@{#1286690}
web-platform-tests · Apr 12, 2024 · 8905c6f · 8905c6f
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diff --git a/css/css-scroll-snap/snap-after-relayout/layout-follows-focused-targeted-block-iframe.html b/css/css-scroll-snap/snap-after-relayout/layout-follows-focused-targeted-block-iframe.html
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+<!DOCTYPE html>
+<html>
+  <body>
+    <style>
+      .scroller {
+        width: 200px;
+        height: 200px;
+        border: solid 1px black;
+        overflow: scroll;
+        scroll-snap-type: both mandatory;
+        position: relative;
+        resize: both;
+      }
+      .target {
+        scroll-snap-align: start;
+        width: 50px;
+        height: 50px;
+        background-color: green;
+        position: absolute;
+      }
+      .target:target {
+        background-color: blue;
+      }
+      .target:focus {
+        background-color: yellow;
+      }
+      #box1 {
+        left: 150px;
+        top: 0px;
+      }
+      #box2 {
+        left: 0px;
+        top: 150px;
+      }
+      .space {
+        width: 500%;
+        height: 500%;
+        position: absolute;
+      }
+    </style>
+    <div class="scroller" id="scroller">
+        <div tabindex="1" id="box1" class="target">Box 1</div>
+        <div tabindex="1" id="box2" class="target">Box 2</div>
+      <div class="space"></div>
+    </div>
+  </body>
+
+</html>
diff --git a/css/css-scroll-snap/snap-after-relayout/layout-follows-focused-targeted-block.html b/css/css-scroll-snap/snap-after-relayout/layout-follows-focused-targeted-block.html
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+<!DOCTYPE html>
+<html>
+  <head>
+    <link rel="help" href="https://drafts.csswg.org/css-scroll-snap" />
+    <script src="/resources/testharness.js"></script>
+    <script src="/resources/testharnessreport.js"></script>
+    <script src="/dom/events/scrolling/scroll_support.js"></script>
+  </head>
+  <body>
+    <style>
+      iframe {
+        width: 1000px;
+        height: 1000px;
+      }
+    </style>
+    <script>
+      let scroller;
+      let box1;
+      let box2;
+      let frame;
+
+      const iframe_load_promise = new Promise((resolve) => {
+        frame = document.createElement("iframe");
+        frame.onload = async () => {
+          scroller = frame.contentDocument.getElementById("scroller");
+          box1 = frame.contentDocument.getElementById("box1");
+          box2 = frame.contentDocument.getElementById("box2");
+          resolve();
+        };
+        frame.src = "./layout-follows-focused-targeted-block-iframe.html#box2";
+        document.body.appendChild(frame);
+      });
+
+      const displacement = 150;
+      async function test_resnap(t, target) {
+        // Save box1's position and setup the cleanup.
+        const box1_left = box1.style.left;
+        t.add_cleanup(async () => {
+          // Reset box1's position.
+          box1.style.left = box1_left;
+          // Reset scroller's writing-mode.
+          scroller.style.writingMode = "horizontal-tb";
+          // Reset scroll position.
+          await waitForScrollReset(t, scroller);
+        });
+
+        assert_equals(scroller.scrollTop, 0, "scroll top is reset");
+        assert_equals(scroller.scrollLeft, 0, "scroll left is reset");
+
+        // Move box1 outside the scrollport by translating it 150px
+        // horizontally.
+        const new_left = box1.offsetLeft + displacement;
+        box1.style.left = `${new_left}px`;
+
+        assert_equals(scroller.scrollLeft, target.offsetLeft,
+          `scroller followed ${target.id} in x axis`);
+
+        assert_equals(scroller.scrollTop, target.offsetTop,
+          `scroller followed ${target.id} in y axis`);
+      }
+
+      promise_test(async (t) => {
+        await iframe_load_promise;
+
+        box1.focus();
+        assert_equals(frame.contentDocument.activeElement, box1,
+          "sanity check that box1 is focused.");
+        assert_equals(frame.contentDocument.querySelector(":target"), box2,
+          "sanity check that box2 is targeted.");
+        // box2 is targeted but box1 is focused, so box1 should be
+        // followed.
+        await test_resnap(t, box1);
+
+        // Remove focus from box1.
+        scroller.focus();
+      }, "focused area prefered over targeted area.");
+
+      promise_test(async (t) => {
+        await iframe_load_promise;
+
+        assert_not_equals(frame.contentDocument.activeElement, box1,
+          "sanity check that box1 is not focused.");
+        assert_equals(frame.contentDocument.querySelector(":target"), box2,
+          "sanity check that box2 is targeted.");
+        // box2 is targeted and box1 is not focused, so box2 should be
+        // followed.
+        await test_resnap(t, box2);
+      }, "targeted area prefered over non-focused area.");
+
+      promise_test(async (t) => {
+        await iframe_load_promise;
+
+        // Clear the targeted element.
+        frame.contentDocument.location.hash = "";
+        assert_equals(frame.contentDocument.querySelector(":target"), null,
+          "sanity check that no box is targeted.");
+        assert_not_equals(frame.contentDocument.activeElement, box1,
+          "sanity check that box1 is not focused.");
+
+        // Neither box is targeted or focused; so, the block axis target should
+        // be followed.
+        await test_resnap(t, box1);
+      }, "block axis area is preferred.");
+
+      promise_test(async (t) => {
+        await iframe_load_promise;
+
+        scroller.style.writingMode = "vertical-lr";
+
+        // Clear the targeted element.
+        frame.contentDocument.location.hash = "";
+        assert_equals(frame.contentDocument.querySelector(":target"), null,
+          "sanity check that no box is targeted.");
+        assert_not_equals(frame.contentDocument.activeElement, box1,
+          "sanity check that box1 is not focused.");
+
+        // Neither box is targeted or focused; so, the block (x) axis target
+        // should be followed.
+        await test_resnap(t, box2);
+      }, "block axis area is preferred (vertical writing-mode).");
+    </script>
+  </body>
+
+</html>