~/nikkyamresh
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active · Mar 2025

WorldBuilder

A C++ plugin for Unreal Engine 5 — click in the viewport to draw road networks with auto-junctions, snapping, and spline-based mesh generation. Also does buildings.

WB
C++ Unreal Engine 5 Spline Mesh Dynamic Mesh Python
GitHub →

The problem

Hand-placing roads in Unreal’s level editor is tedious, and the existing marketplace plugins for procedural roads are either expensive, bloated, or miss the editor UX I wanted. I wanted a “click, click, road” tool that felt native — extend, split, snap — and that also handled buildings so I could block out a whole neighborhood in a morning.

What it does

A UE5 editor-mode plugin with two main tools:

  • Point Capture Tool — click in the viewport to place road points. Roads extend as you go; click an existing road to split it; click near an endpoint to snap and join. Dynamic junction meshes get generated at intersections automatically.
  • Building Generator — three modes (spline-based, polygon-based, area-fill). Choose wall meshes, door frequency, floor heights, roof style. Presets save combinations for reuse.

Plus a Measure Distance tool because I got tired of eyeballing scale in a big level.

Architecture

  • Editor Mode: a proper UEdMode subclass so it lives in the mode palette next to Landscape/Foliage.
  • Road system: splines drive a procedural mesh. Multiple road types (flyover, tunnel, city, countryside) — each type is a config struct with its own mesh params, material, lane count, sidewalk.
  • Junctions: when two roads meet within tolerance, I compute the intersection polygon and build a dynamic mesh for the junction cap, stitched to both splines. That was the hardest part to get looking clean.
  • Building system: spline or polygon defines the footprint; a generator walks the perimeter placing wall meshes; interior floors/stairs added based on height.
  • Python utilities: for advanced batch generation — “give me 200 houses in this grid” without clicking 200 times.

Interesting problems I solved

Junction meshes that don’t T-bone each other. Two perpendicular roads meeting is easy; three or four roads converging at odd angles is not. I ended up computing an approximated centroid, projecting each road’s incoming cross-section inward, and triangulating the bounded polygon. Not analytically perfect but visually clean and fast.

Smart snapping without being annoying. Snap-to-grid is fine but it fights user intent. Tolerance-based snap-to-existing (with a clear visual cue when the snap will engage) turned out to be the right trade-off.

Learning C++ in UE5’s module system from scratch. I’m a Node/TypeScript engineer by day. UE5 has its own macros (UPROPERTY, UCLASS), garbage collection semantics, and build system. The learning curve is real — but procedural geometry was the carrot that pulled me through.

What I’d do differently

  • Start with a slice of vertical — a single road type, junctions, done — before adding configurable road types. I scope-crept early.
  • Write unit tests for the junction math. Debugging a triangulation bug in a 3D editor by eye is a bad time.