vvvv-troubleshooting

name	vvvv-troubleshooting
description	Diagnoses and fixes common vvvv gamma errors in C# nodes, SDSL shaders, and runtime behavior. Use when encountering errors, exceptions, crashes, red nodes, shader compilation failures, missing nodes in the browser, performance issues, or unexpected behavior.
license	CC-BY-SA-4.0
compatibility	Designed for coding AI agents assisting with vvvv gamma development
metadata	{"author":"Tebjan Halm","version":"1.0"}

vvvv gamma Troubleshooting

C# / ProcessNode Issues

"Node" Suffix in Class Name

Symptom: Node works but has ugly name in vvvv. Fix: Remove "Node" suffix — vvvv convention forbids it.

// WRONG
[ProcessNode]
public class SteeringBehaviorNode { }

// CORRECT
[ProcessNode]
public class SteeringBehavior { }

Out Parameters After Inputs

Symptom: Pins appear in wrong order or node doesn't compile correctly. Fix: out parameters must come FIRST in Update signature.

// WRONG
public void Update(float input = 0f, out float result) { ... }

// CORRECT
public void Update(out float result, float input = 0f) { ... }

Node Not Appearing in Node Browser

Symptom: Your C# class exists but doesn't show up in vvvv. Fix: Check these in order:

1. [assembly: ImportAsIs] attribute exists in your project
2. [ProcessNode] attribute on the class
3. Project targets net8.0
4. DLL is in the correct lib/net8.0/ path relative to .vl document
5. Project builds without errors

Allocations Causing Frame Drops

Symptom: GC spikes, stuttering, frame drops. Diagnosis: Allocations in the Update loop.

Common culprits:

• new keyword in Update method
• LINQ operators (.Where(), .Select(), .ToList())
• String concatenation (+ operator on strings)
• Boxing value types (passing int where object expected)

Fix: Cache everything, pre-allocate buffers, eliminate LINQ from hot paths.

Missing Change Detection

Symptom: CPU usage high even when nothing changes. Fix: Compare inputs to cached values, only recompute on change.

if (param != _lastParam)
{
    _cached = Compute(param);
    _lastParam = param;
}
result = _cached; // Always output cached

Downstream Nodes See null/default

Symptom: Connected nodes get no data, even though the node "works". Fix: Always output cached result, even when no computation happens.

// WRONG — output is only set inside the if block
public void Update(out float result, float input = 0f)
{
    if (input != _last)
    {
        result = Compute(input);
        _last = input;
    }
    // result is unassigned when input hasn't changed!
}

// CORRECT — always assign output
public void Update(out float result, float input = 0f)
{
    if (input != _last)
    {
        _cached = Compute(input);
        _last = input;
    }
    result = _cached;
}

SDSL Shader Issues

For SDSL syntax rules, common mistakes, and correct/wrong examples, see vvvv-shaders/syntax-rules.md. Key issues: static const scope, missing semicolons, missing override, enum binding format.

Runtime Issues

Memory Leaks

Symptom: Memory usage grows over time. Causes:

• Missing IDisposable on nodes with native resources
• COM objects (ComPtr<T>) not disposed
• Event handler subscriptions not unsubscribed

Thread Safety

Symptom: Intermittent crashes, data corruption. Fix: Update() runs on the main thread. Capture SynchronizationContext in the constructor, then marshal background results back:

private SynchronizationContext _vlSyncContext;

public MyNode()
{
    _vlSyncContext = SynchronizationContext.Current!;
}

// From background thread:
_vlSyncContext.Post(_ => { /* runs on VL thread */ }, null);

Circular Dependencies

Symptom: vvvv warns about circular dependency, patch won't compile. Fix: Insert a FrameDelay node to break the cycle.

Build Issues

Target Framework Mismatch

Symptom: DLL loads but types aren't found. Fix: Ensure .csproj targets net8.0 (matching vvvv gamma's runtime).

Assembly Version Conflicts

Symptom: FileLoadException or TypeLoadException at runtime. Fix: Align package versions with vvvv's bundled versions. Check vvvv's lib/ folder for reference.

For detailed error-to-solution mapping, see error-catalog.md.