UIRendering

UI Rendering is the process by which a user interface specification, including layout, components, and state, is converted into pixels on a display. It is a core function of UI frameworks across platforms and typically comprises layout, paint, and compositing stages. The layout stage calculates the size and position of each element based on constraints and relationships. The painting stage traverses the render tree and issues drawing commands for visuals such as text, images, and shapes. The compositing stage merges the painted content into the final frame, often using GPU hardware acceleration and a layered representation to improve performance.

Render trees and scene graphs are central data structures in UI rendering. A render tree tracks visual elements and their relationships, while a layer or texture cache may store pre-rendered content to minimize recomputation. Modern systems use double buffering and vertical synchronization to present frames smoothly and avoid tearing.

Performance considerations are critical in UI rendering. Goals include maintaining a target frame rate (commonly 60 frames per second), minimizing re-layout and re-paint, and reducing memory usage. Techniques such as dirty-region invalidation, bitmap caching, tiling of large views, and separating content into independently composited layers help contain cost during interaction and animation.

Platform and framework differences exist in rendering approaches. Native platforms rely on their built-in pipelines (for example, leveraging platform-specific animation and compositor services), while cross-platform frameworks may implement their own render engines (such as using a vector scene and a GPU-accelerated painter). Accessibility, localization, and responsive design considerations are integral to effective UI rendering.