VL File Format (.vl)

Overview

A .vl file is an XML document encoding a visual dataflow program for vvvv gamma. Key elements:

• Document — root element, contains dependencies and one top-level Patch
• Patch — container for visual elements (Nodes, Pads, Links, Canvases)
• Node — operation calls, type definitions, or regions
• Pin — input/output on a Node (defined at definition site)
• Pad — visual data element (IOBox) for displaying/editing values
• Link — connects two endpoints by referencing their IDs
• Canvas — visual grouping container (no logical scope)
• ProcessDefinition — lifecycle definition (Create, Update) via Fragments
• Slot — state field within a type definition

XML Root and Namespaces

<?xml version="1.0" encoding="utf-8"?>
<Document xmlns:p="property" xmlns:r="reflection" Id="C2vqbtoStWoOI1eKIKZBBM"
          LanguageVersion="2024.6.0" Version="0.128">
  <!-- dependencies and patch -->
</Document>

Root attributes: Id (base62 GUID), LanguageVersion (e.g. "2024.6.0"), Version (always "0.128").

ID System

Every element has a unique Id — a 22-character base62-encoded GUID using [0-9A-Za-z]. All IDs must be unique within the document. Generate via GUIDEncoders.GuidTobase62(Guid.NewGuid()).

Link Ids attribute: comma-separated "sourceId,sinkId" (output first, input second).

Element Hierarchy

Document
├── NugetDependency (0..n)
├── DocumentDependency (0..n)
├── PlatformDependency (0..n)
└── Patch (exactly 1, top-level)
    ├── Canvas (DefaultCategory, CanvasType="FullCategory")
    └── Node (Name="Application")
        └── Patch (inner)
            ├── Canvas (CanvasType="Group")
            │   ├── Node (operation calls)
            │   ├── Pad (IOBoxes)
            │   └── ...
            ├── Patch (Name="Create")
            ├── Patch (Name="Update")
            ├── ProcessDefinition
            │   ├── Fragment → Create patch
            │   └── Fragment → Update patch
            └── Link (0..n)

Critical: Dependencies are direct children of Document, NOT inside Patch.

Dependencies

<NugetDependency Id="..." Location="VL.CoreLib" Version="2024.6.0" />
<DocumentDependency Id="..." Location="./MyOtherFile.vl" />
<PlatformDependency Id="..." Location="VL.Core.dll" />

Almost every document needs VL.CoreLib. Use IsForward="true" to re-export types to consumers.

NodeReference System (Choices)

The <p:NodeReference> property defines what a Node IS. It contains <Choice> elements that identify the target symbol.

Operation Call

<p:NodeReference LastCategoryFullName="Primitive.Math" LastDependency="CoreLibBasics.vl">
  <Choice Kind="NodeFlag" Name="Node" Fixed="true" />
  <Choice Kind="OperationCallFlag" Name="+" />
</p:NodeReference>

• First Choice: Kind="NodeFlag" with Fixed="true" (shape indicator)
• Second Choice: ProcessAppFlag (stateful) or OperationCallFlag (stateless)

Type Definitions

<!-- Process -->
<Choice Kind="ContainerDefinition" Name="Process" />
<CategoryReference Kind="Category" Name="Primitive" />

<!-- Class / Record / Interface / Forward -->
<Choice Kind="ClassDefinition" Name="Class" />
<Choice Kind="RecordDefinition" Name="Record" />
<Choice Kind="InterfaceDefinition" Name="Interface" />
<Choice Kind="ForwardDefinition" Name="Forward" />

Regions

<Choice Kind="StatefulRegion" Name="Region (Stateful)" Fixed="true" />
<CategoryReference Kind="Category" Name="Primitive" />
<Choice Kind="ApplicationStatefulRegion" Name="If" />  <!-- or ForEach, Cache -->

Regions use StatefulRegion as the FIRST Choice (not NodeFlag). Use ApplicationStatefulRegion for If/ForEach or ProcessStatefulRegion for Cache.

Node Element

<Node Name="MyNode" Bounds="300,200,65,19" Id="...">
  <p:NodeReference>...</p:NodeReference>
  <Pin Id="..." Name="Input" Kind="InputPin" />
  <Pin Id="..." Name="Output" Kind="OutputPin" />
</Node>

Key attributes: Id, Name, Bounds ("X,Y" or "X,Y,W,H"), Summary, Tags.

Pin Element

<Pin Id="..." Name="Value" Kind="InputPin" DefaultValue="42" />
<Pin Id="..." Name="Result" Kind="OutputPin" />

Kind values: InputPin, OutputPin, StateInputPin, StateOutputPin, ApplyPin.

Visibility: Visible (default), Optional, OnCreateDefault, Hidden.

Pad Element (IOBox)

<Pad Id="..." Bounds="200,160,80,20" ShowValueBox="true" isIOBox="true" Value="3.14"
     Comment="My Value">
  <p:TypeAnnotation LastCategoryFullName="Primitive" LastDependency="CoreLibBasics.vl">
    <Choice Kind="TypeFlag" Name="Float32" />
  </p:TypeAnnotation>
</Pad>

Note the lowercase i in isIOBox. Common types: Boolean, Int32, Float32, Float64, String, Vector2, Vector3.

Comment Pad

<Pad Id="..." Bounds="100,100,400,25" ShowValueBox="true" isIOBox="true"
     Value="Title text here">
  <p:TypeAnnotation><Choice Kind="TypeFlag" Name="String" /></p:TypeAnnotation>
  <p:ValueBoxSettings>
    <p:fontsize p:Type="Int32">14</p:fontsize>
    <p:stringtype p:Assembly="VL.Core" p:Type="VL.Core.StringType">Comment</p:stringtype>
  </p:ValueBoxSettings>
</Pad>

Link Element

<Link Id="..." Ids="outputPinId,inputPinId" />

Ids format: "sourceId,sinkId" — output first, input second. Use IsFeedback="true" for feedback loops, IsHidden="true" for reference links.

ProcessDefinition and Fragments

<Patch Id="innerPatchId">
  <Canvas Id="..." CanvasType="Group" />
  <Patch Id="createId" Name="Create" />
  <Patch Id="updateId" Name="Update" />
  <ProcessDefinition Id="...">
    <Fragment Id="..." Patch="createId" Enabled="true" />
    <Fragment Id="..." Patch="updateId" Enabled="true" />
  </ProcessDefinition>
</Patch>

Fragment Patch attribute references a sibling <Patch> element's Id.

Regions

Regions use 4-value Bounds ("X,Y,W,H") and have ControlPoints at borders:

<Node Bounds="100,200,400,300" Id="...">
  <p:NodeReference LastCategoryFullName="Primitive" LastDependency="Builtin">
    <Choice Kind="StatefulRegion" Name="Region (Stateful)" Fixed="true" />
    <CategoryReference Kind="Category" Name="Primitive" />
    <Choice Kind="ApplicationStatefulRegion" Name="If" />
  </p:NodeReference>
  <Patch Id="...">
    <Canvas Id="..." CanvasType="Group"><!-- content --></Canvas>
    <Patch Id="thenId" Name="Then" />
    <Fragment Id="..." Patch="thenId" Enabled="true" />
  </Patch>
  <ControlPoint Id="..." Bounds="150,200" Alignment="Top" />
  <ControlPoint Id="..." Bounds="150,500" Alignment="Bottom" />
</Node>

Region patch names: If uses Then/Else, ForEach uses Create/Update/Dispose, Cache uses Create/Update.

TypeAnnotation

<!-- Simple type -->
<p:TypeAnnotation>
  <Choice Kind="TypeFlag" Name="Float32" />
</p:TypeAnnotation>

<!-- Generic type: Spread<RGBA> -->
<p:TypeAnnotation LastCategoryFullName="Collections" LastDependency="VL.Collections.vl">
  <Choice Kind="TypeFlag" Name="Spread" />
  <p:TypeArguments>
    <TypeReference LastCategoryFullName="Color" LastDependency="CoreLibBasics.vl">
      <Choice Kind="TypeFlag" Name="RGBA" />
    </TypeReference>
  </p:TypeArguments>
</p:TypeAnnotation>

Slot Element (State Fields)

<Slot Id="..." Name="MyField">
  <p:TypeAnnotation><Choice Kind="TypeFlag" Name="Float32" /></p:TypeAnnotation>
  <p:Value>0.5</p:Value>
</Slot>

Complete Minimal Example

<?xml version="1.0" encoding="utf-8"?>
<Document xmlns:p="property" Id="A1b2C3d4E5f6G7h8I9j0Kl"
          LanguageVersion="2024.6.0" Version="0.128">
  <NugetDependency Id="B2c3D4e5F6g7H8i9J0k1Lm" Location="VL.CoreLib"
                   Version="2024.6.0" />
  <Patch Id="C3d4E5f6G7h8I9j0K1l2Mn">
    <Canvas Id="D4e5F6g7H8i9J0k1L2m3No" DefaultCategory="Main"
            BordersChecked="false" CanvasType="FullCategory" />
    <Node Name="Application" Bounds="100,100" Id="E5f6G7h8I9j0K1l2M3n4Op">
      <p:NodeReference>
        <Choice Kind="ContainerDefinition" Name="Process" />
        <CategoryReference Kind="Category" Name="Primitive" />
      </p:NodeReference>
      <Patch Id="F6g7H8i9J0k1L2m3N4o5Pq">
        <Canvas Id="G7h8I9j0K1l2M3n4O5p6Qr" CanvasType="Group" />
        <Patch Id="H8i9J0k1L2m3N4o5P6q7Rs" Name="Create" />
        <Patch Id="I9j0K1l2M3n4O5p6Q7r8St" Name="Update" />
        <ProcessDefinition Id="J0k1L2m3N4o5P6q7R8s9Tu">
          <Fragment Id="K1l2M3n4O5p6Q7r8S9t0Uv"
                   Patch="H8i9J0k1L2m3N4o5P6q7Rs" Enabled="true" />
          <Fragment Id="L2m3N4o5P6q7R8s9T0u1Vw"
                   Patch="I9j0K1l2M3n4O5p6Q7r8St" Enabled="true" />
        </ProcessDefinition>
      </Patch>
    </Node>
  </Patch>
</Document>

Validation Rules

1. All IDs must be unique (22-char base62 GUIDs)
2. xmlns:p="property" must be on Document
3. Version="0.128" always required
4. Fragment Patch must reference existing sibling Patch IDs
5. Link Ids: exactly "sourceId,sinkId" — output first
6. CanvasType="FullCategory" only for root canvas
7. Every document needs VL.CoreLib dependency
8. Application node is the entry point (Name="Application", ContainerDefinition)
9. Element names are case-sensitive (Patch not patch)
10. isIOBox uses lowercase i
11. Dependencies are children of Document, not Patch

Common Mistakes

• Forgetting xmlns:p="property" namespace declaration
• Putting dependencies inside Patch instead of Document
• Reversed Link direction (first ID must be source/output)
• Missing ProcessDefinition for process/class type definitions
• Wrong Bounds format (use commas, no spaces: "100,200,65,19")
• Using IsIOBox instead of isIOBox

For the complete element reference with all attributes, Choice kinds, and serialization details, see [format-reference.md](format-reference.md). For layout conventions, spacing, positioning, and visual organization best practices, see [best-practices.md](best-practices.md).