YUP Audio Plugin - Build Guide

Five steps from empty folder to a working CLAP/VST3/standalone plugin. Do each step in order; skip none.

Step 1 - Project setup (CMake + YUP)

• Add YUP as a git submodule or FetchContent target; disable examples/tests for plugin projects unless needed.
• Use yup_audio_plugin (...) to declare the plugin target.
• Set TARGET_NAME, TARGET_VERSION, TARGET_APP_ID, TARGET_APP_NAMESPACE, and TARGET_CXX_STANDARD 20.
• Set plugin metadata in the same call: PLUGIN_ID, PLUGIN_NAME, PLUGIN_VENDOR, PLUGIN_VERSION, PLUGIN_DESCRIPTION, PLUGIN_IS_SYNTH, and PLUGIN_IS_MONO.
• Enable only the formats you need: PLUGIN_CREATE_CLAP, PLUGIN_CREATE_VST3, PLUGIN_CREATE_STANDALONE.
• Link at least yup::yup_gui and yup::yup_audio_processors in MODULES.
• Add plugin sources to ${target_name}_shared; the format targets link against that shared interface target.

Step 2 - AudioProcessor skeleton

• Subclass yup::AudioProcessor.
• Construct it with a processor name and immutable yup::AudioBusLayout, e.g. stereo output: AudioProcessor ("MyPlugin", yup::AudioBusLayout ({}, { yup::AudioBus ("main", yup::AudioBus::Audio, yup::AudioBus::Output, 2) })).
• Override prepareToPlay (float sampleRate, int maxBlockSize), releaseResources(), processBlock (yup::AudioSampleBuffer& audioBuffer, yup::MidiBuffer& midiBuffer), and flush().
• In prepareToPlay: store sample rate, allocate worst-case scratch storage, initialise AudioParameterHandles, and reset all filters, envelopes, oscillators, delay lines, MIDI/voice state, and smoothers.
• In processBlock: assume realtime constraints; no allocation, locks, yup::String formatting, logging, file/network access, or UI calls.
• Implement preset and state methods: getCurrentPreset, setCurrentPreset, getNumPresets, getPresetName, setPresetName, loadStateFromMemory, and saveStateIntoMemory.
• Export the plugin entry point:

extern "C" yup::AudioProcessor* createPluginProcessor()
{
    return new MyPluginProcessor();
}

Step 3 - Parameters via AudioParameterBuilder

• Add parameters in the processor constructor with addParameter (...).
• Keep each yup::AudioParameter::Ptr as a processor member; parameter IDs must be stable and unique.
• Use yup::AudioParameterBuilder().withID (...).withName (...).withRange (...).withDefault (...).withSmoothing (...).build().
• For audio-thread reads, construct a yup::AudioParameterHandle in prepareToPlay with the parameter and sample rate.
• In processBlock, call handle.updateNextAudioBlock() once per block, then use getNextValue() per sample or skip (numSamples) for block ramps.
• From the editor, wrap user drags with beginChangeGesture() and endChangeGesture(), and use setValueNotifyingHost() for host-visible parameter changes.
• For presets or state restore, prefer setting the real value with setValue() or setNormalizedValue() from a non-audio thread, then let the audio handle pick it up next block.

Step 4 - Editor and UI

• Subclass yup::AudioProcessorEditor.
• Implement isResizable(), getPreferredSize(), paint (yup::Graphics&), and resized().
• The editor owns UI components; the processor must work correctly with no editor open.
• The editor may keep AudioParameter::Ptrs and poll values from a yup::Timer for display sync.
• Do not store a raw editor pointer in the processor. Use hasEditor() and createEditor() as the factory boundary.
• UI controls should notify parameters through gestures, e.g. slider drag start/end plus setValueNotifyingHost().

Step 5 - Build, test, package

• Configure: cmake -B build -DCMAKE_BUILD_TYPE=Release -DYUP_BUILD_TESTS=OFF -DYUP_BUILD_EXAMPLES=OFF
• Build: cmake --build build --config Release
• Validate the produced CLAP/VST3/standalone targets in at least one host.
• Test sample-rate changes, buffer-size changes, transport reset, preset recall, automation, MIDI timing, bypass/suspend/resume, and editor open/close.
• If the plugin reports latency or tail, override getLatencySamples() and getTailSamples() and verify hosts receive correct values.

Common pitfalls

Pitfall	Correct approach
Reading raw AudioParameter values directly for smoothed DSP	Use AudioParameterHandle initialised in prepareToPlay
Forgetting updateNextAudioBlock()	Call it once at the top of each audio block before getNextValue() or skip()
Calling setValueNotifyingHost() from processBlock	Use it from UI/host-control paths; keep audio-thread changes local or lock-free
Allocating MIDI voices on note-on	Preallocate a bounded voice pool in prepareToPlay
Hard-coding stereo processing without matching AudioBusLayout	Declare the layout explicitly and guard channel access
Missing state methods	Implement loadStateFromMemory / saveStateIntoMemory; hosts depend on them for recall
Holding getProcessLock() from UI/background work	Keep state swaps short; the CLAP wrapper uses a try-lock around processing
Leaving state stale after prepareToPlay or flush()	Reset voices, smoothers, filter history, delay buffers, and pending MIDI unconditionally

Use the yup-review skill to audit finished processor code for YUP-specific thread, parameter, wrapper, and bus-layout issues.