| name | downspout-extend-plugin |
| description | Extend or modify behavior in an existing downspout plugin. Use when Codex is asked to add controls, DSP or MIDI behavior, transport/state handling, serialization, UI elements, or tests inside a plugin directory while preserving the portable-core plus thin-DPF-wrapper architecture. |
Downspout Extend Plugin
Use this skill for changes inside an existing plugins/<plugin>/ directory.
Workflow
- Read
AGENTS.md, the plugin README.md, and any plugin docs/ notes before editing.
- Identify the host-agnostic behavior first. Keep DSP, MIDI, scheduling, state normalization, and serialization in the portable core.
- Keep DPF code as glue: parameter declarations, host transport conversion, state forwarding, audio/MIDI buffer adaptation, and UI.
- Prefer plugin-local edits. Do not modify
third_party/, src/common/, include/downspout/, root CMake/install/release scripts, or shared workflows unless the user explicitly approves.
- Update tests before or with behavior changes. Prefer deterministic core tests over manual DAW verification.
- Update plugin-local docs when behavior, state, parameters, transport assumptions, or UI workflow changes.
Common edit paths
For parameters and controls, update in this order:
plugins/<plugin>/include/*_core_types.hpp or equivalent parameter struct and defaults.- Clamp/sanitize logic in the core.
- Text serialization/deserialization and old-state fallback defaults.
plugins/<plugin>/include/*_params.hpp parameter IDs, appending new IDs when compatibility matters.src/dpf/*Plugin.cpp initParameter, getParameterValue, setParameterValue, and any output-status mapping.src/dpf/*UI.cpp local UI state, control definitions, current-parameter conversion, interaction handling, and layout.tests/*_core_tests.cpp coverage for defaults, clamp, serialization, and behavior.
For transport-aware behavior, explicitly test stopped transport, first play block, loop/rewind boundaries, tempo/grid changes, and hold/recover/scatter-style triggers when present.
For UI changes, remove or move text before shrinking functional controls. Keep labels readable at the fixed plugin window size and make controls reflect processor output status where possible.
Read references/plugin-patterns.md when you need concrete file patterns, reference plugins, or parameter/state checklists.
