PCG: Road, Forest and Vehicle

Background & Goals

Procedural generation is widely used in both large open-world games and indie titles, so I set out to make it part of my portfolio and a key area of future research. This project focuses on terrain-based procedural road generation. To enhance the visuals, it uses terrain-driven material assignment and node editing inspired by Electric Dream, with Unreal Engine's native racing system integrated to showcase the final result.

Pathfinding in Houdini

Cost field design — every terrain point is weighted by multiple factors, and paths generate along low-cost regions:

• Slope cost: using each mesh point's normal unit vector, the dot product (negatively correlated with slope) yields higher cost for steeper areas
• Ascend / Descend cost: surface slope at each point is computed from lines to adjacent points (a calculus-based approach); steeper points cost more
• Convexity / Concavity cost: the measure_curvature node separates convex from concave regions — rivers form where concavity is high, animal trails where slopes are gentle
• User attribute / Slump cost: heightfield_maskbyfeature classifies points above a slope threshold as cliffs

Remesh optimization: Houdini's built-in Remesh node caused excessive overhead when the heightmap was finely divided. A Custom Mesh node triangulating the heightfield gave more controlled density and significantly reduced computation time.

Spline serialization: supports multiple start points and destinations, allowing several disconnected paths.

Spline Editing Tools in Unreal

Via the Public API, the tool instantiates a Houdini actor in Unreal, retrieves parameters and triggers a recook — a full "delete original path, recook new path" editing loop:

• Left click creates a new spline point or inserts one into a segment; Ctrl + left click deletes the selected point
• A Gizmo is created for each spline for direct in-editor adjustment
• Worldtrace (custom function): keeps points anchored to the ground while dragging
• Snap to Ground (custom function): snaps spline points to the terrain on recook

Automatic Landscape Material

Terrain mask data from Houdini drives a landscape layer array in Unreal, assigning materials in order and staying compatible with the path tool (paint layer parameters for man-made roads, animal paths, rivers, etc. are exposed in Houdini). Visual optimization: tile density decreases as the camera approaches the ground and texture density increases in the distance to reduce repetition (fade distance 1000 vs 5000).

Electric Dream PCG Node Editing

I integrated the Electric Dream PCG asset pack and manually adjusted its nodes to match the project's terrain and road generation rules:

• Restricted foliage generation height to a specific range
• Adjusted point placement logic to avoid spawning trees and large rocks on slopes
• Filtered road areas via landscape layers to prevent vegetation on roads

Final Outcome

A complete "Houdini algorithm + UE editing tool" path generation pipeline that artists can adjust directly in-editor, demonstrated with UE's native racing system.