From 82278d632f4305da9867c37c2101bf99565e7172 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 22 Feb 2021 23:44:51 +0100
Subject: [PATCH] LibWeb: Only scroll BlockBox on wheel event if
 overflow==scroll

We implement this by adding a BlockBox::is_scrollable() helper,
and then ignoring wheel events for non-scrollable boxes.

Thanks to FireFox317 for pointing this out! :^)
---
 Userland/Libraries/LibWeb/Layout/BlockBox.cpp | 8 ++++++++
 Userland/Libraries/LibWeb/Layout/BlockBox.h   | 1 +
 Userland/Libraries/LibWeb/Layout/Node.cpp     | 2 ++
 3 files changed, 11 insertions(+)

diff --git a/Userland/Libraries/LibWeb/Layout/BlockBox.cpp b/Userland/Libraries/LibWeb/Layout/BlockBox.cpp
index a23d33d1e2..d46b743721 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockBox.cpp
+++ b/Userland/Libraries/LibWeb/Layout/BlockBox.cpp
@@ -142,6 +142,12 @@ void BlockBox::split_into_lines(InlineFormattingContext& context, LayoutMode lay
     line_box->add_fragment(*this, 0, 0, border_box_width(), height());
 }
 
+bool BlockBox::is_scrollable() const
+{
+    // FIXME: Support horizontal scroll as well (overflow-x)
+    return computed_values().overflow_y() == CSS::Overflow::Scroll;
+}
+
 void BlockBox::set_scroll_offset(const Gfx::FloatPoint& offset)
 {
     if (m_scroll_offset == offset)
@@ -152,6 +158,8 @@ void BlockBox::set_scroll_offset(const Gfx::FloatPoint& offset)
 
 void BlockBox::handle_mousewheel(Badge<EventHandler>, const Gfx::IntPoint&, unsigned int, unsigned int, int wheel_delta)
 {
+    if (!is_scrollable())
+        return;
     auto new_offset = m_scroll_offset;
     new_offset.move_by(0, wheel_delta);
     set_scroll_offset(new_offset);
diff --git a/Userland/Libraries/LibWeb/Layout/BlockBox.h b/Userland/Libraries/LibWeb/Layout/BlockBox.h
index 470b78ad64..5d6951a0e0 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockBox.h
+++ b/Userland/Libraries/LibWeb/Layout/BlockBox.h
@@ -53,6 +53,7 @@ public:
 
     virtual void split_into_lines(InlineFormattingContext&, LayoutMode) override;
 
+    bool is_scrollable() const;
     const Gfx::FloatPoint& scroll_offset() const { return m_scroll_offset; }
     void set_scroll_offset(const Gfx::FloatPoint&);
 
diff --git a/Userland/Libraries/LibWeb/Layout/Node.cpp b/Userland/Libraries/LibWeb/Layout/Node.cpp
index 0893fb3416..e62a688513 100644
--- a/Userland/Libraries/LibWeb/Layout/Node.cpp
+++ b/Userland/Libraries/LibWeb/Layout/Node.cpp
@@ -321,6 +321,8 @@ void Node::handle_mousemove(Badge<EventHandler>, const Gfx::IntPoint&, unsigned,
 void Node::handle_mousewheel(Badge<EventHandler>, const Gfx::IntPoint&, unsigned, unsigned, int wheel_delta)
 {
     if (auto* containing_block = this->containing_block()) {
+        if (!containing_block->is_scrollable())
+            return;
         auto new_offset = containing_block->scroll_offset();
         new_offset.move_by(0, wheel_delta);
         containing_block->set_scroll_offset(new_offset);