LibGUI: Introduce widget content margins + improve splitters

A GUI::Widget can now set an optional content margin (4x0 by default.)
Pixels in the content margin will be ignored for hit testing purposes.

Use this to allow frame-like widgets (like GUI::Frame!) to ignore any
mouse events in the frame area, and instead let those go to parent.

This allows GUI::Splitter to react "sooner" to mouse events that were
previously swallowed by the child widgets instead of ending up in the
splitter. The net effect is that 2 more pixels on each side of a
splitter handle are now interactive and usable for splitting! :^)

1 files changed, 18 insertions, 1 deletions

diff --git a/Libraries/LibGUI/Widget.cpp b/Libraries/LibGUI/Widget.cpp
index 00b107a5f4..ceee7e37f3 100644
--- a/Libraries/LibGUI/Widget.cpp
+++ b/Libraries/LibGUI/Widget.cpp
@@ -472,7 +472,7 @@ Widget* Widget::child_at(const Gfx::Point& point) const
         auto& child = Core::to<Widget>(children()[i]);
         if (!child.is_visible())
             continue;
-        if (child.relative_rect().contains(point))
+        if (child.content_rect().contains(point))
             return const_cast<Widget*>(&child);
     }
     return nullptr;
@@ -811,4 +811,21 @@ void Widget::did_end_inspection()
     update();
 }
 
+void Widget::set_content_margins(const Margins& margins)
+{
+    if (m_content_margins == margins)
+        return;
+    m_content_margins = margins;
+    invalidate_layout();
+}
+
+Gfx::Rect Widget::content_rect() const
+{
+    auto rect = relative_rect();
+    rect.move_by(m_content_margins.left(), m_content_margins.top());
+    rect.set_width(rect.width() - (m_content_margins.left() + m_content_margins.right()));
+    rect.set_height(rect.height() - (m_content_margins.top() + m_content_margins.bottom()));
+    return rect;
+}
+
 }