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xtc/docs/ARCHITECTURE.md
hanez 1d8f869b5b Initial commit.
2026-10-26 22:51:25 +01:00

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Architecture

Decision: modular engine first

The processing graph is the common model for audio sources, instruments, effects, mixers, and outputs. The sequencer produces time-based content and events consumed by graph nodes. The default workspace remains sequencer-first; the graph editor is an advanced view of the same project.

Layers

  1. FLTK/C++ GUI: input, drawing, windows, view state.
  2. C core: project model, commands, parameters, persistence, validation.
  3. C engine: prepared processing graph, DSP, transport timing, event delivery.
  4. Backend: hardware and system audio/MIDI integration.

The GUI must not directly modify engine internals. It calls a stable C API.

Graph execution

The first implementation should reject cycles. Compile a graph off the audio thread: validate, topologically sort, determine buffer requirements, allocate resources, and publish a prepared immutable execution plan. The audio thread must not traverse a graph being edited.

The current scaffold is deliberately incomplete: xt_graph_process_offline() validates the graph and applies gain nodes in insertion order. It is a test placeholder, not the final graph execution algorithm.

Ownership and threads

  • GUI thread owns FLTK widgets and view state.
  • Project/control thread owns mutable project data and graph compilation.
  • Audio thread owns the active processing plan and DSP state.
  • Backend callbacks follow the backend's documented threading contract.

Do not free an active plan until the audio thread has released it. Pick and document a bounded handoff/reclamation strategy before real-time graph swaps.