1.9 KiB
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
- FLTK/C++ GUI: input, drawing, windows, view state.
- C core: project model, commands, parameters, persistence, validation.
- C engine: prepared processing graph, DSP, transport timing, event delivery.
- 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 offline engine now copies a validated graph into a prepared plan with stable node IDs, topological order, precomputed input adjacency, per-node mono buffers and oscillator/meter state. Each plan has one processing owner. Graph edits and destruction cannot affect an existing plan. All nodes are scheduled, including disconnected nodes; only explicit output nodes are rendered (or terminal nodes when no output node exists). See AUDIO_ENGINE.md for contracts. Plan publication across threads and retirement remain Phase 2 work.
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.