vvvv-troubleshooting

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Translated

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.

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Translated version includes tags in frontmatter
vvvv-gamma-troubleshootingcsharp-node-issuessdsl-shader-fixesruntime-problem-solvingbuild-error-resolution

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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.
csharp
// 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.
csharp
// 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.
csharp
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.
csharp
// 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:
csharp
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.