Fix clamping of scroll position in window.scrollBy

For rightward and downward overflow the spec says: Let x be max(0, min(x, viewport scrolling area width - viewport width)). Let y be max(0, min(y, viewport scrolling area height - viewport height)). Previously, those operations were reversed, which created negative overflow even when the overflow direction was downward. This change ensures that Servo matches spec behavior.
servo · May 11, 2017 · b13cf11 · b13cf11
1 parent 0040160
commit b13cf11
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Showing 3 changed files with 38 additions and 2 deletions.
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
@@ -1066,8 +1066,8 @@ impl Window {
                 let content_size = e.upcast::<Node>().bounding_content_box_or_zero();
                 let content_height = content_size.size.height.to_f64_px();
                 let content_width = content_size.size.width.to_f64_px();
-                (xfinite.max(0.0f64).min(content_width - width),
-                 yfinite.max(0.0f64).min(content_height - height))
+                (xfinite.min(content_width - width).max(0.0f64),
+                 yfinite.min(content_height - height).max(0.0f64))
             },
             None => {
                 (xfinite.max(0.0f64), yfinite.max(0.0f64))

diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -19783,6 +19783,12 @@
      {}
     ]
    ],
+   "mozilla/scrollBy.html": [
+    [
+     "/_mozilla/mozilla/scrollBy.html",
+     {}
+    ]
+   ],
    "mozilla/scrollTo.html": [
     [
      "/_mozilla/mozilla/scrollTo.html",
@@ -31354,6 +31360,10 @@
    "b247e3a0ba733c1a8b129ce2994b862d8ed3a423",
    "testharness"
   ],
+  "mozilla/scrollBy.html": [
+   "0243d584bc615a73ea1667fc35f5d73b5165d19f",
+   "testharness"
+  ],
   "mozilla/scrollTo.html": [
    "b9917be5fed364dbc46264f641f54f275b5c054a",
    "testharness"

diff --git a/tests/wpt/mozilla/tests/mozilla/scrollBy.html b/tests/wpt/mozilla/tests/mozilla/scrollBy.html
@@ -0,0 +1,26 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Ensure that the window.scrollBy function affects scroll position as expected</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+    <a id="link" href="http://mozilla.org">This is some link text.</a>
+    <div style="width: 10000px; height: 10000px; background: pink; z-index: -1;"></div>
+    <script>
+    test(function() {
+        scrollBy(0, 5000);
+        assert_equals(scrollX, 0);
+        assert_equals(pageXOffset, 0);
+        assert_equals(scrollY, 5000);
+        assert_equals(pageYOffset, 5000);
+
+        scrollTo(0, 0);
+
+        var link = document.getElementById("link");
+        var linkRect = link.getBoundingClientRect();
+        assert_equals(link, document.elementFromPoint(linkRect.left, linkRect.top));
+        window.scrollBy(0, 1);
+        assert_equals(link, document.elementFromPoint(linkRect.left, linkRect.top - 1));
+    });
+    </script>
+</body>