From Heightmaps to Influence Maps: Rewriting Terrain Generation in a Hex-Based 3D RTS

The Problem with Heightmaps

When I first built the terrain system for my hex-based 3D RTS in Godot, I went with the obvious approach: heightmaps. Elevation dictated everything—sea, land, cliffs, biomes. Simple. Predictable. And way too rigid.

I hit the wall fast. Want tundra at low elevations because of magical frost wells? Nope. Desert on high plateaus but only near trade routes? Not without hacks. The moment gameplay elements like buildings or resources needed to affect terrain, I was stuck juggling spaghetti logic that checked height first, then applied exceptions. It didn’t scale. It didn’t breathe.

The final straw was a commit titled terrain sort of working. It wasn’t sarcastic. It was a surrender. I’d hardcoded SEA/LAND/CLIFF thresholds into the mesh generation, and every new feature made it worse. I needed out.

A Shift to Influence-Driven Terrain

So I ripped it all out.

Instead of asking "How high is this hex?", the new system asks: "What influences this tile, and how strong are they?"

Now, terrain type emerges from layered influence maps. Each hex stores float values for factors like water, heat, magic, civilization, or decay. Biomes aren’t tied to elevation—they’re derived from combinations of these influences. A desert forms where heat is high and water is low. A swamp emerges from high water and high decay. Tundra? High magic and low heat, regardless of height.

But here’s the kicker: those influences aren’t static. Units, buildings, and resources actively push values around. A fortress raises civilization influence, gradually turning scrubland into farmland. A necromancer’s tower pumps decay, corrupting nearby forests into bogs. Even elevation can be a result of influence—say, when terraforming units compress earth influence into raised terrain.

This isn’t just prettier terrain. It’s gameplay baked into the world. Players don’t just move on the map—they shape it, and the map pushes back.

Building It in Godot: Data, Hexes, and Updates

Godot’s flexibility made this pivot possible, but it still took careful architecture.

I represent the world as a HexGrid using axial coordinates (q, r). Each hex has a data container with influence values, stored in a Dictionary for quick access:

var influences = {
    "water": 0.0,
    "heat": 0.0,
    "civilization": 0.0,
    "decay": 0.0
}

Influence sources—like a farm or an oasis—register themselves with the InfluenceManager. Every frame (or on a staggered update for performance), the manager applies falloff and diffusion using a simple flood-fill over hex neighbors. The strength at each tile is a weighted sum, clamped and normalized.

Biome determination happens in a separate system that reads the final influence state. I use a priority-based rule set:

if influences["water"] > 0.8 and influences["decay"] > 0.6:
    return BIOME_SWAMP
elif influences["civilization"] > 0.7 and influences["water"] > 0.4:
    return BIOME_FARMLAND

This decouples biome logic from influence propagation—critical for iteration. Want cities to create suburbs instead of farmland? Tweak the rules, not the math.

Mesh generation now runs after biome assignment. Elevation is just another output—possibly influenced by biome, but not the driver. Cliffs? They’re generated where biome or elevation changes too rapidly between hexes, with Godot’s SurfaceTool stitching the geometry.

Performance was a concern, but by updating influences in chunks and using Godot’s PhysicsServer3D for spatial queries when needed, it runs smooth even on larger maps.

Why This Matters for Indie RTS Devs

If you’re building an RTS—especially in Godot—don’t lock yourself into height-driven terrain early. It feels safe, but it’s a trap. The real magic happens when the world reacts. Influence maps aren’t just for AI pathfinding or strategic scoring. They can be the foundation of your entire world model.

This rewrite let me delete more code than I wrote. The system is more flexible, more readable, and actually fun to extend. Next up: letting players drop terraforming abilities that inject influence pulses directly.

The terrain isn’t just a stage anymore. It’s part of the conversation.