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What is Noise?

Noise in world generation refers to pseudo-random mathematical functions that create natural-looking patterns. Unlike true randomness (which looks chaotic), noise functions create smooth, continuous variation — perfect for terrain, clouds, and organic shapes. Iris uses noise for:
  • Terrain height (mountains, valleys, plains)
  • Biome distribution (where biomes spawn)
  • Block variation (stone mixed with andesite)
  • Feature placement (tree density, grass coverage)
Think of noise as “controlled randomness.” It’s predictable (same seed = same output) but looks organic and natural.

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Noise Dimensions

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2D Noise (X, Z)

Used for:
  • Terrain height (Y-value based on X/Z position)
  • Biome placement
  • Surface decoration density
Input: (x, z)
Output: value (typically -1.0 to 1.0)

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3D Noise (X, Y, Z)

Used for:
  • Caves (3D carving)
  • Ore veins
  • Density functions
  • 3D biome blending
Input: (x, y, z)
Output: value (typically -1.0 to 1.0)

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Noise Types in Iris

Iris provides multiple noise algorithms through the NoiseStyle enum:

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Simplex Noise

SIMPLEX - Smooth, organic noise 
{
  "style": "SIMPLEX",
  "zoom": 0.5
}
Characteristics:
  • Very smooth gradients
  • No directional bias
  • Fast computation
  • Good for: Natural terrain, hills, general-purpose use

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Perlin Noise

PERLIN - Classic gradient noise 
{
  "style": "PERLIN",
  "zoom": 0.4
}
Characteristics:
  • Slightly more grid-aligned than Simplex
  • Smooth transitions
  • Good for: Classic terrain, gentle slopes

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Cellular Noise (Worley)

CELLULAR - Cell-based patterns 
{
  "style": "CELLULAR",
  "zoom": 1.0
}
Characteristics:
  • Creates distinct cells/regions
  • Sharp transitions
  • Voronoi diagram-based
  • Good for: Plateaus, mesas, biome borders, cracked terrain

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Fractal Noise Variants

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Fractal Billow

FRACTAL_BILLOW_SIMPLEX - Billowy, cloud-like 
{
  "style": "FRACTAL_BILLOW_SIMPLEX",
  "zoom": 0.3,
  "fractalOctaves": 3
}
Characteristics:
  • Rounded, puffy features
  • Multiple octaves for detail
  • Good for: Rolling hills, dunes, clouds

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Fractal Rigid Multi

FRACTAL_RIGID_MULTI_SIMPLEX - Sharp ridges 
{
  "style": "FRACTAL_RIGID_MULTI_SIMPLEX",
  "zoom": 0.4,
  "fractalOctaves": 4
}
Characteristics:
  • Sharp, rigid ridges
  • Excellent for mountain ranges
  • Creates dramatic peaks
  • Good for: Mountains, canyons, sharp terrain

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Fractal FBM (Fractional Brownian Motion)

FRACTAL_FBM_SIMPLEX - Layered detail 
{
  "style": "FRACTAL_FBM_SIMPLEX",
  "zoom": 0.5,
  "fractalOctaves": 5
}
Characteristics:
  • Standard fractal layering
  • Each octave adds detail
  • Good for: Natural terrain with fine detail

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Noise Parameters

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Zoom (Frequency)

Controls feature size 
{
  "zoom": 0.2  // Large features (continental scale)
}

{
  "zoom": 2.0  // Small features (rocky detail)
}
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zoom
number
default:"1.0"
Noise frequency/scale. Lower = larger features, higher = smaller features.Typical ranges:
  • 0.05-0.2: Continental/regional features
  • 0.3-0.8: Hills and valleys
  • 1.0-3.0: Local detail
  • 4.0+: Fine texture

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Fractal Octaves

Adds layered detail 
{
  "fractalOctaves": 1  // Smooth, simple
}

{
  "fractalOctaves": 5  // Detailed, complex
}
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fractalOctaves
integer
default:"1"
Number of noise layers for fractal types. Each octave adds finer detail.
  • 1: Simple, smooth noise
  • 2-3: Moderate detail (recommended)
  • 4-6: High detail (performance cost)
  • 7+: Very detailed (heavy performance impact)
Each octave roughly doubles computation time. Keep octaves under 6 for production worlds.

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Seed

Deterministic variation 
{
  "seed": 12345
}
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seed
integer
Custom seed for this noise layer. Same seed = same pattern. If omitted, uses world seed.

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Advanced Techniques

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Domain Warping (Fracture)

Warp coordinate space before sampling noise: 
{
  "style": "SIMPLEX",
  "zoom": 0.5,
  "fracture": {
    "style": "SIMPLEX",
    "zoom": 0.1,
    "multiplier": 25
  }
}
How it works:
  1. Sample fracture noise at (x, z)
  2. Offset coordinates: x′ = x + fracture_x, z′ = z + fracture_z
  3. Sample main noise at (x′, z′)
Result: Flowing, organic patterns instead of regular noise
Fracture is the secret to natural-looking terrain. Use it on most terrain generators with multiplier 15-35.

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Noise Interpolation

Smooth blending between different noise values: 
{
  "interpolator": "HERMITE"
}
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interpolator
IrisInterpolator
Smoothing function:
  • LINEAR: Sharp transitions
  • HERMITE: Smooth (default for most uses)
  • BEZIER: Very smooth

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Exponent (Noise Shaping)

Shape the noise curve: 
{
  "exponent": 2.0  // Favor lower values (flatter terrain)
}

{
  "exponent": 0.5  // Favor higher values (more peaks)
}
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exponent
number
default:"1.0"
Power applied to noise output. Values greater than 1.0 create more flat areas, less than 1.0 create more peaks.

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Practical Examples

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Natural Hills

{
  "style": "FRACTAL_BILLOW_SIMPLEX",
  "zoom": 0.35,
  "fractalOctaves": 3,
  "fracture": {
    "style": "SIMPLEX",
    "zoom": 0.12,
    "multiplier": 20
  }
}
Why this works:
  • Billow creates rounded hills
  • Fracture adds organic flow
  • 3 octaves provide natural detail

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Dramatic Mountains

{
  "style": "FRACTAL_RIGID_MULTI_SIMPLEX",
  "zoom": 0.5,
  "fractalOctaves": 5,
  "fracture": {
    "style": "CELLULAR",
    "zoom": 0.2,
    "multiplier": 30
  }
}
Why this works:
  • Rigid multi creates sharp peaks
  • Cellular fracture adds angular warping
  • 5 octaves provide rocky detail

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Plateaus and Mesas

{
  "style": "CELLULAR",
  "zoom": 0.6,
  "exponent": 1.5
}
Why this works:
  • Cellular creates distinct regions
  • Exponent flattens the cells
  • Result: Flat-topped plateaus

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Debugging Noise

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Visualization Tips

1

Use Studio Mode

/iris studio for real-time testing
2

Fly high

View terrain from Y=200+ to see large-scale patterns
3

Adjust one parameter at a time

Change zoom, then octaves, then fracture separately
4

Use debug overlays

Enable height debug in Iris settings

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Common Issues

Solution: Add fracture or increase fractal octaves
{
  "fracture": {
    "style": "SIMPLEX",
    "zoom": 0.1,
    "multiplier": 20
  }
}
Solution: Reduce zoom, decrease octaves
{
  "zoom": 0.3,  // Was 1.5
  "fractalOctaves": 2  // Was 6
}
Solution: Increase generator multiplier or use sharper noise
{
  "style": "FRACTAL_RIGID_MULTI_SIMPLEX",  // Was SIMPLEX
  "multiplier": 30  // Was 10
}
Solution: Reduce octaves, simplify fracture
{
  "fractalOctaves": 3,  // Was 7
  "fracture": null  // Remove if not needed
}

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Best Practices

  1. Start with SIMPLEX: It’s fast and versatile
  2. Use fracture for realism: 80% of generators benefit from it
  3. Keep octaves reasonable: 2-4 for most cases
  4. Test at different scales: Fly high and walk on ground
  5. Combine noise types: SIMPLEX for base + CELLULAR for variation

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Next Steps

Generators

Apply noise in terrain generators

Expressions

Use noise in mathematical expressions

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