Unreal Large Blueprint Analysis

Large Blueprint Analysis

Systematic strategy for reading, understanding, and translating large Blueprints (10+ sections, 100+ nodes). Builds on the unreal-blueprint-editing and unreal-object-operation skills.

Prerequisite: UE editor running with UCP plugin enabled. Read the unreal-blueprint-editing skill first for API details.

Why This Skill Exists

Large Blueprints can have 40+ sections and 1000+ nodes. A single ReadGraph call for the EventGraph alone can return 100KB+ of text. Naive approaches fail because:

• Reading all sections at once exceeds context window limits
• Skipping sections and "guessing" from general knowledge produces inaccurate code
• Unstructured reading leads to missed dependencies between functions

Phase 1 — Inventory

Get the complete structure before reading any graph content.

Step 1.1: List all sections

{"object":"/Script/UnrealClientProtocolEditor.Default__NodeCodeEditingLibrary","function":"Outline","params":{"AssetPath":"<asset_path>"}}

Record the full list. Categorize each section:

Step 1.2: Read the Blueprint's variables

Use unreal-object-operation skill's DescribeObject to get all UPROPERTY variables on the Blueprint's CDO. This reveals the full state model — every variable the Blueprint uses.

{"object":"/Script/UnrealClientProtocol.Default__ObjectOperationLibrary","function":"DescribeObject","params":{"ObjectPath":"<blueprint_default_object_path>"}}

The CDO path for a Blueprint class MyBlueprint_C in package /Game/BP/MyBlueprint is: /Game/BP/MyBlueprint.Default__MyBlueprint_C

Step 1.3: Build a section dependency map

Before reading graph content, infer dependencies from section names:

• Function:Initialize likely calls Function:SetupRT, Function:SetCaptureMesh, etc.
• EventGraph likely calls most functions and responds to UI events
• Macros are called by functions — read the caller first, then the macro when you encounter it

Phase 2 — Systematic Reading

Rule: Read sections in dependency order, not alphabetical order. Process each section completely before moving to the next.

Reading strategy

1. Read one section at a time — keep output manageable
2. Start with entry points — EventGraph first, then Construct/PreConstruct
3. Follow the call chain — when a section calls Function:Foo, queue Function:Foo for reading
4. Use a SubAgent for each section's pseudocode translation — see below

Use SubAgents for pseudocode translation

For each section you read, launch a SubAgent to translate the NodeCode into pseudocode. This is critical for large Blueprints because:

• Raw NodeCode for a 50-node function easily fills 5KB+ of text — it will crowd out your reasoning context
• SubAgent processes the NodeCode in isolation, returns a compact pseudocode summary
• You keep only the pseudocode in your main context, staying focused on the big picture

SubAgent prompt template:

Translate the following Blueprint NodeCode into pseudocode. Trace execution flow from entry nodes, resolve all data dependencies into inline expressions.

(paste the ReadGraph output here)

Return:

1. Pseudocode (one line per statement, with comments for non-obvious logic)
2. Summary: what this section does, what variables it reads/writes, what functions it calls

Workflow per section:

1. ReadGraph → get NodeCode
2. Launch SubAgent with the NodeCode → get pseudocode back
3. Record the pseudocode summary in your main context
4. Move to next section

Reading template

Read one section at a time:

{"object":"/Script/UnrealClientProtocolEditor.Default__NodeCodeEditingLibrary","function":"ReadGraph","params":{"AssetPath":"<path>","Section":"Function:Initialize"}}

Handling large outputs

If a single section's ReadGraph output exceeds ~50KB (e.g., a 200+ node EventGraph):

1. Read it alone (not batched with other sections)
2. If the Shell output is written to a file, split and read in chunks
3. Focus on extracting: node types, function calls, variable reads/writes, and link topology
4. For EventGraph specifically, identify all event handlers (Event:*, K2Node_ComponentBoundEvent) as separate logical blocks

Pseudocode translation

CRITICAL: After reading each section, immediately translate the NodeCode into pseudocode. This is the most important step — NodeCode describes structure, not logic. You must reconstruct the control flow and data flow to understand what the section actually does.

1. Find the entry node (FunctionEntry, Event, CustomEvent)
2. Follow then/execute exec links to build statement order
3. At each node, resolve data inputs by tracing backwards through data links
4. Collapse math/utility chains into inline expressions
5. Branch → if/else, ForEachLoop → for, Sequence → sequential blocks

Section summary format

After translating each section, record a summary like:

## Function:Initialize
- Pseudocode:
    if Orthographic:
        OrthoWidth = ObjectRadius * 2
        ProjectionType = Orthographic
    else:
        FOVAngle = Clamp(CameraFOV, 10, 170)
        ProjectionType = Perspective
    SceneCapture.TextureTarget = CreateRT(...)
    SetupShowOnlyList(SceneCapture, TargetMeshes)
    DynamicMesh.SetMaterial(0, CreateMID(BaseMaterial))
    ResetAllCaptureModes()
- Calls: SetupRTAndSaveList, SetCaptureMeshAndSizeInfo, SetupOctahedronLayout, ClearRenderTargets, CreateAndSetupMIDs, ResetAllCaptureModes
- Reads: SceneCaptureComponent2D, StaticMeshComponent, DynamicMeshComponent, CaptureUsingGBuffer, Orthographic, CameraDistance, ObjectRadius
- Writes: OrthoWidth, FOVAngle, ProjectionType, TextureTarget, CurrentMapIndex
- Nodes: 47

Phase 3 — Translation

When converting Blueprint to C++, follow these rules:

Variable mapping

1. All Blueprint variables → UPROPERTY members on a UObject or grouped into settings/state structs
2. Blueprint enums (UserDefinedEnum) → C++ UENUM with different names to avoid conflicts
3. Blueprint structs (UserDefinedStruct) → C++ USTRUCT with different names
4. Local variables in functions → local C++ variables

Function mapping

Node-by-node translation

For each node in a section, translate directly:

Execution flow reconstruction

Links define the execution order. Reconstruct C++ control flow by:

1. Find the entry node (FunctionEntry, Event, CustomEvent)
2. Follow then/execute exec pins to build the statement sequence
3. At Branch nodes, create if/else blocks
4. At Sequence nodes, emit statements in order (then_0, then_1, ...)
5. Data flow pins become variable assignments or inline expressions

Material / MPC references

When the Blueprint references content assets (materials, MPC, textures):

1. Record every asset path referenced in node properties (e.g., pin.Collection:/Game/MPC/MyMPC.MyMPC)
2. In C++, load these via LoadObject<T>(nullptr, TEXT("/Path/To/Asset")) or ConstructorHelpers::FObjectFinder
3. If creating an independent plugin, copy the referenced assets and update all paths

Phase 4 — Verification

Completeness check

After translation, verify every section has been processed:

1. Re-read the Outline output
2. Check off each section against your C++ implementation
3. Any unprocessed section = missing functionality

Compile and test

1. Build with UBT using -Module=YourModule to isolate compilation
2. Fix errors iteratively
3. If UE editor is running, use UCP to test the C++ code at runtime

Anti-Patterns