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SSBO + quad pipeline for UI rendering ​

Context ​

UI rectangles and text were rendered through multiple code paths: rectangles used one shader/pipeline, text used another (MSDF), images used a third. Each path had its own buffer management, draw calls, and state tracking. This fragmented the renderer and made batch optimizations difficult.

Decision ​

Unify all 2D UI rendering (rectangles, text, images) onto a single SSBO-backed instanced quad pipeline. All primitives are instances of a single quad geometry, with per-instance data (position, size, color, texture coordinates, clip rects) packed into SSBOs. Text is handled as instanced glyphs within the same pipeline.

Commit: refactor(ui): unify ui rectangles/text on SSBO+quad pipeline (2026-03-07)

Consequences ​

Positive:

  • Single draw-call path for all UI — massive reduction in draw calls
  • Instanced rendering with minimal CPU overhead
  • Consistent clip rect handling across all primitives
  • Easier to add new UI primitive types (just add instance data)

Negative:

  • All primitives must fit the quad + instance data model
  • Custom rendering (e.g., non-rectangular primitives) needs separate paths
  • SSBO requires GL 4.3+ (acceptable for the target platforms)