SDL3 migration

Context

The project initially used SDL2 for windowing and input. SDL3 brought a redesigned API with:

• More explicit event handling
• Modernized GPU API (removing legacy fixed-function paths)
• Better Wayland and cross-platform support
• Different coordinate and touch semantics

The migration happened as part of the large Lua branch merge (2026-02-04 to 2026-02-25), touching both the C++ engine and the Lua/Fennel input layer.

Decision

Migrate the entire runtime from SDL2 to SDL3, vendoring SDL3 in external/. All input handling, window creation, and event loops use the new SDL3 API.

Consequences

Positive:

• Cleaner input abstraction with explicit state tracking
• Better Wayland/multi-monitor handling
• Foundation for cross-platform work (Windows support followed in June 2026)

Negative:

• Touch and pointer coordinates diverged, requiring follow-up hardening (fix(input): restore consistent touch and pointer coordinates, 2026-04-22)
• Required extensive engine-side changes to input semantics and event flow
• CEF integration needed SDL3-specific window parent/embed logic

Related

• Goal: Core Platform — SDL3 underpins windowing and input for the platform
• Subsystems — Engine section
• See src/ for SDL3 initialization and event loop