Debugging vvvv gamma C# Projects

For CLI arguments and session files, see the vvvv-startup skill.

Context-Aware Setup Workflow

When the user asks to set up debugging, follow this workflow. Ask ALL configuration questions upfront using AskUserQuestion before generating any files. Do NOT assume defaults — always confirm with the user.

1. Detect vvvv Installation

Find vvvv.exe automatically by scanning C:\Program Files\vvvv\ for vvvv_gamma_* directories:

ls -d "/c/Program Files/vvvv/vvvv_gamma_"* 2>/dev/null | sort -r

Directory name format: vvvv_gamma_MAJOR.MINOR[-BUILD-gHASH-PLATFORM]. Sort by version descending. Filter out -beta, -alpha, -rc, -test, -dev variants unless no stable version exists.

2. Scan Workspace

Detect what exists in the workspace:

.csproj / .sln files (may or may not need build tasks -- see step 3)
.vl files (candidates for --open)
help/ folders (common location for test patches)
Existing .vscode/launch.json (extend rather than overwrite)
Git submodules (especially VL.StandardLibs — see package repos warning below)
Package names from repo folder name, main *.vl file or .csproj <PackageId> (for --editable-packages)

3. Ask User — ALL Questions Before Generating

CRITICAL: Ask all of these questions using AskUserQuestion BEFORE generating any configuration. Use multi-question format to batch related questions. Do not generate launch.json until all answers are collected.

Question Group 1: vvvv Version & Patch

Which vvvv version? — Present detected versions, recommend the latest stable. Let user pick or specify a custom path.
Which .vl patch to open? — List found .vl files as options. If help/ folder exists, suggest those.

Question Group 2: Launch Flags

--debug flag? — Enables debug symbols for breakpoints but slows patching. Ask: "Enable --debug for breakpoints? (slower startup)" Default: No for fast iteration, Yes if user explicitly wants breakpoints.
--allowmultiple? — Allows launching a second vvvv instance. Ask: "Allow multiple vvvv instances? If No, launch will fail if vvvv is already running (useful to detect stale instances)." Default: No.
--package-repositories? — Points vvvv to scan a folder for packages. WARNING: If the workspace contains git submodules like VL.StandardLibs/, using --package-repositories ${workspaceFolder} will cause vvvv to recompile ALL core libraries from source, taking many minutes. Ask: "Add --package-repositories? Only needed if vvvv can't find your package. WARNING: if your repo has VL.StandardLibs or other library submodules, this will trigger full recompilation." Default: No.
--editable-packages? — Loads specified packages from source. Only useful with --package-repositories. Ask only if package-repositories is enabled.

Question Group 3: Build Mode

Source reference or DLL? — "Does your .vl document reference the .csproj directly (source reference, most common) or a pre-built DLL?" Source reference = no build task. DLL = add preLaunchTask: "build".

4. Generate Configuration

Only after all questions are answered, generate .vscode/launch.json and optionally .vscode/tasks.json.

Always generate these configurations:

A launch config with the user's chosen flags
An "Attach to vvvv" config for attaching to an already-running instance

Optionally generate:

A second launch config with --debug if the first one doesn't have it (or vice versa)
A tasks.json if DLL/binary build mode was selected

VS Code launch.json

Minimal Config (source reference, no extras)

The simplest possible config — just open a patch:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "vvvv — MyPatch",
      "type": "coreclr",
      "request": "launch",
      "program": "C:\\Program Files\\vvvv\\vvvv_gamma_7.1-win-x64\\vvvv.exe",
      "args": [
        "-o",
        "${workspaceFolder}/help/HowTo Use MyFeature.vl"
      ],
      "cwd": "${workspaceFolder}",
      "stopAtEntry": false,
      "console": "internalConsole"
    },
    {
      "name": "Attach to vvvv",
      "type": "coreclr",
      "request": "attach",
      "processName": "vvvv.exe"
    }
  ]
}

Full Config (with all optional flags)

When the user opts in to all flags:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Debug with vvvv",
      "type": "coreclr",
      "request": "launch",
      "program": "C:\\Program Files\\vvvv\\vvvv_gamma_7.0-win-x64\\vvvv.exe",
      "args": [
        "--package-repositories",
        "${workspaceFolder}",
        "--editable-packages",
        "VL.MyPackage*",
        "-o",
        "${workspaceFolder}/help/HowTo Use MyFeature.vl",
        "--debug",
        "--allowmultiple"
      ],
      "cwd": "${workspaceFolder}",
      "stopAtEntry": false,
      "console": "internalConsole"
    },
    {
      "name": "Attach to vvvv",
      "type": "coreclr",
      "request": "attach",
      "processName": "vvvv.exe"
    }
  ]
}

DLL/Binary Reference (external build required)

Add preLaunchTask to build C# before launching vvvv:

{
  "name": "Debug with vvvv (pre-build)",
  "type": "coreclr",
  "request": "launch",
  "preLaunchTask": "build",
  "program": "C:\\Program Files\\vvvv\\vvvv_gamma_7.0-win-x64\\vvvv.exe",
  "args": [
    "-o",
    "${workspaceFolder}/help/HowTo Use MyFeature.vl",
    "--debug"
  ],
  "cwd": "${workspaceFolder}",
  "stopAtEntry": false,
  "console": "internalConsole"
}

Key points:

Omit preLaunchTask for source references -- vvvv handles C# compilation via Roslyn
Add preLaunchTask: "build" only for DLL/binary references or complex build scenarios
--debug enables debug symbols (needed for breakpoints, but slows down patching)
--package-repositories tells vvvv where to find your package — WARNING: will recompile any VL library submodules found in the scanned folder tree
--editable-packages loads specified packages from source (glob patterns supported)
-o opens the specified .vl patch on startup
--allowmultiple allows a second vvvv instance — omit to detect stale instances
Use array items for args (not a single string) for readability

Attach to Running vvvv

Use attach when vvvv is already running and you want to debug without restarting:

{
  "name": "Attach to vvvv",
  "type": "coreclr",
  "request": "attach",
  "processName": "vvvv.exe"
}

VS Code tasks.json (only for DLL/binary reference setups)

Only generate tasks.json when the project requires external building (DLL references, native dependencies, Release builds). Skip this entirely for source project references where vvvv compiles C# at runtime.

Build with dotnet

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "build",
      "command": "dotnet",
      "type": "process",
      "args": ["build", "${workspaceFolder}/src/MyProject.csproj", "-c", "Debug"],
      "problemMatcher": "$msCompile",
      "group": { "kind": "build", "isDefault": true }
    },
    {
      "label": "build-release",
      "command": "dotnet",
      "type": "process",
      "args": ["build", "${workspaceFolder}/src/MyProject.csproj", "-c", "Release"],
      "problemMatcher": "$msCompile"
    }
  ]
}

Build with MSBuild (for .sln or projects requiring Visual Studio toolchain)

{
  "version": "2.0.0",
  "tasks": [
    {
      "label": "build",
      "type": "shell",
      "command": "& 'C:\\Program Files\\Microsoft Visual Studio\\2022\\Community\\MSBuild\\Current\\Bin\\MSBuild.exe' '${workspaceFolder}/src/MyProject.sln' -p:Configuration=Debug -p:Platform=x64 -t:Rebuild -v:minimal",
      "options": {
        "shell": { "executable": "powershell.exe", "args": ["-Command"] }
      },
      "problemMatcher": "$msCompile",
      "group": { "kind": "build", "isDefault": true }
    }
  ]
}

Prefer dotnet build unless the project requires MSBuild-specific features or a .sln with platform targets.

Visual Studio Setup

Debug via External Program

Open .csproj in Visual Studio
Debug > Debug Properties (or Project Properties > Debug > General)
Create a new launch profile:
- Command: path to vvvv.exe
- Command line arguments: -o YourPatch.vl (add --debug when breakpoints are needed)
- Working directory: project folder
Press F5 to launch with debugger attached

Attach to Process

Launch vvvv normally (add --debug if you need breakpoints)
Debug > Attach to Process (Ctrl+Alt+P)
Find vvvv.exe in the process list
Select Managed (.NET Core, .NET 5+) as code type
Click Attach

launchSettings.json (dotnet tooling)

{
  "profiles": {
    "Debug vvvv": {
      "commandName": "Executable",
      "executablePath": "C:\\Program Files\\vvvv\\vvvv_gamma_6.8-win-x64\\vvvv.exe",
      "commandLineArgs": "-o YourPatch.vl",
      "workingDirectory": "$(ProjectDir)"
    }
  }
}

Debugging Tips

--debug -- forces debug symbol emission for reliable breakpoints, but adds overhead. Use in the Debug config; omit for performance/deployment testing.
--stoppedonstartup -- launch paused so you can set breakpoints before any Update() runs
--nocache -- if breakpoints won't bind, force recompilation from source
Debugger.Break() -- add to C# code to programmatically trigger a breakpoint
Conditional breakpoints in Update() -- Update() runs every frame, so use hit counts or conditions
Constructor breakpoints -- fire on each live-reload cycle too (Dispose then new Constructor)
console: "internalConsole" -- captures Console.WriteLine output in VS Code debug console
Debugger-attached behavior -- when a .NET debugger is attached, vvvv initialization runs synchronously (no async exception trapping), so startup breakpoints work reliably

Common Pitfalls

--package-repositories + VL.StandardLibs submodule — If your workspace has a VL.StandardLibs/ git submodule (common in vvvv contrib repos), --package-repositories ${workspaceFolder} will cause vvvv to discover and recompile ALL standard libraries from source. This takes many minutes and is almost never what you want. Either omit --package-repositories or point it at a specific subfolder that doesn't contain library submodules.
--allowmultiple hiding stale instances — Without this flag, vvvv refuses to start if another instance is running. This is useful: it tells you there's a stale vvvv process. With --allowmultiple, you might accidentally run two instances consuming double resources.
--debug slowing everything — Debug symbol emission significantly slows vvvv's live compilation. Only enable when you actually need breakpoints. For quick iteration (testing UI, checking behavior), omit it.

vvvv-debugging