Skia, WebRender, Servo pipeline and wgpu rendering architectures

Document status: reviewed. Canonical source.

Summary

Skia demonstrates a broad mature 2D API across raster/GPU/PDF/SVG targets. Servo explicitly separates DOM/script, layout box/fragment trees, display-list generation and WebRender. wgpu supplies a safe cross-platform Rust API over Vulkan, Metal, D3D12 and WebGPU-class backends.

NUIF relevance

The reference implementation should preserve a renderer-independent display/scene boundary. Interactive GPU rendering and normative conformance rendering can use different backends while sharing the same lowered scene semantics.