danzig-gain

danzig-gain

The gain plugin. This is the source that gets compiled for both architectures and packaged into DanzigGain.vst3.

What it demonstrates

A step up from ../danzig-minimal. Where the minimal example uses the lock-free ParamStore, this one uses the heap-backed Plugin and ParameterMap types from src/plugin.zig, and it writes out a VST3 factory with a real vtable.

Plugin lifecycle. init, deinit, setupProcessing(sampleRate), activate, deactivate. The host drives these in order, and process passes audio through unchanged until activate has been called.

A parameter with a plain range. A danzig.Parameter with id 0, titled "Gain", in units of dB, spanning -48 to +48. setParameterNormalized denormalizes the incoming [0, 1] value and pushes the result into the GainProcessor.

Gain staging with a ramp. danzig.GainProcessor converts dB to linear and interpolates toward the target rather than stepping, so parameter moves do not click.

A VST3 factory. PluginFactory is an extern struct whose first field is a pointer to a static IPluginFactoryVTable. GetPluginFactory returns its address. A host reads the first machine word as the vtable pointer and calls through it, which is exactly the C++ object layout the SDK expects.

Build

From the repository root:

zig build

Produces zig-out/lib/libDanzigGain.dylib for your native architecture.

Package as a VST3 bundle

zig build vst3
lipo -info zig-out/DanzigGain.vst3/Contents/MacOS/DanzigGain

Architectures in the fat file: zig-out/DanzigGain.vst3/Contents/MacOS/DanzigGain are: x86_64 arm64

The bundle:

find zig-out/DanzigGain.vst3 -type f

zig-out/DanzigGain.vst3/Contents/Info.plist
zig-out/DanzigGain.vst3/Contents/PkgInfo
zig-out/DanzigGain.vst3/Contents/MacOS/DanzigGain

Install

zig build install-vst3

Removes any previous copy and writes a fresh one to ~/Library/Audio/Plug-Ins/VST3/DanzigGain.vst3. macOS only.

Verify:

lipo -info ~/Library/Audio/Plug-Ins/VST3/DanzigGain.vst3/Contents/MacOS/DanzigGain

Architectures in the fat file: /Users/you/Library/Audio/Plug-Ins/VST3/DanzigGain.vst3/Contents/MacOS/DanzigGain are: x86_64 arm64

What a host currently does with it

Finds the bundle, finds the entry point, and reports zero instantiable classes. factory_getClassInfo writes nothing into the host's buffer and factory_createInstance returns without producing an object, so there is nothing for the host to load.

/Applications/pluginval.app/Contents/MacOS/pluginval \
  --validate zig-out/DanzigGain.vst3 --strictness-level 5 --timeout-ms 20000

Num plugins found: 0
!!! Test 1 failed: No types found.
FAILED!!  1 test failed, out of a total of 1

The parts that do work are verifiable. The symbol is exported:

nm -gU zig-out/DanzigGain.vst3/Contents/MacOS/DanzigGain | grep -i factory

00000000000004c8 T _GetPluginFactory

The bundle is ad-hoc signed by the linker:

codesign -dvv zig-out/DanzigGain.vst3

Format=bundle with Mach-O universal (x86_64 arm64)
CodeDirectory v=20400 size=242 flags=0x20002(adhoc,linker-signed) hashes=4+0 location=embedded
Signature=adhoc

And the factory answers the ABI calls a host makes first. ../danzig-test checks that on every zig build test.

Finishing the plugin means populating getClassInfo with a PClassInfo and returning real IComponent and IAudioProcessor objects from createInstance. The interface declarations are already in src/vst3.zig.

Files

• root.zig. The plugin, the factory, and the entry point.

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See docs/WIKI.md for how the bundle is built and what the factory contract is.