OpenHeightmap

Quick Start

1. Open Unity 6 with URP.
2. Copy the Assets/OpenHeightmap folder into your project.
3. Go to Tools > OpenHeightmap (or press Ctrl+Alt+H).
4. Pick a preset from the Presets tab, or configure parameters manually.
5. Click Generate. The heightmap appears in the live preview.
6. Click Export to save it as PNG, RAW16, or EXR, or Apply to Terrain to write it to the active terrain in the scene.

If the scene has no terrain, Apply to Terrain offers to create one. Its size comes from New Terrain in the Noise tab: with Match Size To Resolution on, width and length follow the resolution (1025 → 1024 × 1024); turn it off to set them yourself. Auto Height (on by default) sets the height as a percentage of the width (Height (% of width), 40% unless a preset sets its own) so new terrains have natural proportions; turn it off to type a height. If the scene already has a terrain, Apply to Terrain updates that one and keeps its size; the New Terrain section says so, and warns when heightmap samples would be more than 4 units apart (for example a 513 map stretched over 64,000 units), which makes terrain look soft and flat. Each new terrain gets its own TerrainData asset in Assets/OpenHeightmap Generated. Generated files are kept outside the tool folder, so updating or removing the tool never touches your terrains.

Features

Processing Pipeline

Each generation run executes passes in strict order. Only enabled passes run.

Normalization stretches the result to fill [0, 1]. Height Multiplier is applied after it: below 1 lowers the whole terrain, above 1 raises lowlands and slopes with a smooth curve that never flattens the peaks.

Noise is sampled in a fixed reference space (512 units across the map), so the same settings give the same terrain at every resolution — a higher resolution adds detail instead of zooming out. Seed changes the terrain for every noise type.

Noise Algorithms

Erosion Simulation

Filters

Splatmaps

Auto-generate terrain layer weights from height and slope. Each biome rule defines a height range and a maximum slope in real degrees (worked out from the terrain's height-to-width ratio: the active terrain's, or the New Terrain size). Weights are smooth-stepped for natural blending. Where a spot is too steep for every rule at its height, the height match is kept rather than falling back to the first layer.

Height Weight sets how sharply height bands separate (0 = height ignored). Slope Weight sets how strictly Max Slope is enforced (0 = slope ignored, 1 = a layer fades out over 10° past its Max Slope).

Click Generate Splatmap in the Splatmap tab to see a color-coded preview (toggle Splat in the toolbar to switch back to the heightmap). Generating a new heightmap clears the splatmap. Apply to Terrain writes it too: it is resampled to a power-of-two alphamap (513 → 512), each splat rule gets a solid-colour TerrainLayer asset in Assets/OpenHeightmap Generated/TerrainLayers (reused on later applies). Applying again, for example after switching presets, swaps those generated layers for the current rules' colours. A layer you assigned yourself (such as a real texture) keeps its slot and is never replaced.

Presets

Each preset keeps your current Resolution and Seed, and sets the New Terrain Height (% of width) to a value that suits it, so gentle presets don't come out mountainous. You can change that slider afterwards. Presets also set the Splatmap rules: Canyon, Plateau, Desert Dunes, Tundra and Volcanic bring their own layers and colors (red rock, sand, moss, ash and so on), and the rest use the default water, sand, grass, rock and snow layers. Edit the rules freely afterwards; Reset to Defaults in the Splatmap tab goes back to the default layers.

API Reference

public interface INoiseProvider
{
    string Name { get; }
    float Sample(float x, float y, int seed = 0);
}

var generator = new HeightmapGenerator();
var parameters = new HeightmapGeneratorParameters { ... };
HeightmapData result = generator.Generate(parameters);

HeightmapData hm = new HeightmapData(513);
float h = hm.GetHeight(x, y);
float hBilinear = hm.GetHeightBilinear(u, v); // 0-1 UV coordinates
float[] flat = hm.ToFlatArray();
HeightmapData clone = hm.Clone();

HeightmapExporter.Export(heightmap, "/path/to/output.png", ExportFormat.PNG);
HeightmapExporter.Export(heightmap, "/path/to/output.raw", ExportFormat.RAW16);

string status = TerrainApplier.Apply(heightmap, new NewTerrainSettings(), "Assets/MyTerrains", "My Terrain");

File Structure

Assets/OpenHeightmap/
├── Documentation/
│   └── Index.html              ← this file
├── Editor/
│   ├── OpenHeightmapWindow.cs  Main EditorWindow (6 tabs + preview)
│   ├── PreviewRenderer.cs      CPU / GPU preview (rendered once per change)
│   ├── HeightmapExporter.cs    PNG / RAW16 / EXR export
│   ├── TerrainApplier.cs       Apply to Terrain (shared with OpenStamper)
│   ├── OpenHeightmap.Editor.asmdef
│   └── Presets/
│       └── TerrainPresets.cs   10 terrain presets
├── Runtime/
│   ├── HeightmapData.cs        Core float[,] wrapper
│   ├── HeightmapGenerator.cs   Pipeline orchestrator
│   ├── OpenHeightmap.Runtime.asmdef
│   ├── Noise/
│   │   ├── INoiseProvider.cs   Interface
│   │   ├── PerlinNoise.cs
│   │   ├── SimplexNoise.cs
│   │   ├── VoronoiNoise.cs
│   │   ├── WorleyNoise.cs
│   │   ├── ValueNoise.cs
│   │   └── MidpointDisplacement.cs
│   ├── Erosion/
│   │   ├── HydraulicErosion.cs
│   │   └── ThermalErosion.cs
│   ├── Filters/
│   │   ├── GaussianBlur.cs
│   │   ├── LaplacianSmooth.cs
│   │   ├── FalloffGenerator.cs
│   │   └── DomainWarping.cs
│   ├── Sampling/
│   │   ├── PoissonDiskSampler.cs
│   │   └── CellularAutomata.cs
│   └── Splat/
│       └── SplatmapGenerator.cs
└── Shaders/
    ├── PreviewCompute.compute  GPU heightmap-to-color
    └── PreviewShader.shader    URP preview material

Companion Tool: OpenStamper