ScrollableArea vs PaintLayerScrollableArea

The provided text explains the architectural relationship between ScrollableArea and PaintLayerScrollableArea (PLSA) within Blink, the rendering engine for Chromium. ScrollableArea serves as an abstract base class that defines the essential interface and shared logic for all scrollable viewports, managing high-level tasks such as animations, scrollbar coordination, and input event handling. In contrast, PLSA is a concrete implementation specifically designed to manage the scrollable overflow of individual elements by linking their layout metrics and geometry to the scrolling system. The sources detail how these classes divide responsibilities, with PLSA handling element-specific duties like scrollbar creation, sticky positioning, and scroll anchoring. Additionally, the text describes how Blink coordinates scrolling between the main thread and the compositor thread to ensure smooth performance. Together, these systems integrate with layout, painting, and developer tools to provide a consistent and efficient scrolling experience across the web.