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Overview

Density functions control terrain shape and cave generation in Minecraft. Lithostitched adds specialized density function types for preserving original terrain data while allowing modifications through worldgen modifiers.

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Density Function Types

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Merged Density Function

Holds references to both original and modified density functions, allowing the system to maintain access to the root density function while applying modifications. Java Interface: 
public record MergedDensityFunction(
    DensityFunction original,
    DensityFunction wrapped,
    DensityFunction full
) implements DensityFunction {
    @Override
    public double compute(FunctionContext context) {
        return this.full.compute(context);
    }
    
    private static DensityFunction unwrappedOriginal(DensityFunction df) {
        return df instanceof MergedDensityFunction merged 
            ? unwrappedOriginal(merged.original()) 
            : df;
    }
}
Source: MergedDensityFunction.java:11-52 Purpose:
  • Preserves the original density function for reference
  • Stores the wrapped (modified) version
  • Executes the full (combined) density function
  • Enables recursive unwrapping to find root functions
JSON Serialization: 
{
  "type": "lithostitched:merged",
  "original": {
    "type": "minecraft:noise",
    "noise": "minecraft:offset"
  }
}
When serialized, MergedDensityFunction only saves the original function to prevent duplication. The wrapped and full functions are regenerated on load.

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Original Marker Density Function

A marker type that indicates a reference to the original, unmodified density function. Java Interface: 
public class OriginalMarkerDensityFunction implements MarkerFunction {
    // No computation - throws exception if called
    @Override
    public double compute(FunctionContext context) {
        throw new IllegalStateException("Marker density function should never be computed!");
    }
}
Source: OriginalMarkerDensityFunction.java:8-16 Purpose:
  • Acts as a placeholder in density function graphs
  • Signals that the original function should be used
  • Never actually executed - resolved before computation
JSON Format: 
{
  "type": "lithostitched:original_marker"
}
Usage in Modifiers: 
{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "modifier": {
    "type": "minecraft:add",
    "argument1": {
      "type": "lithostitched:original_marker"
    },
    "argument2": {
      "type": "minecraft:noise",
      "noise": "mymod:terrain_variation",
      "xz_scale": 0.25,
      "y_scale": 1.0
    }
  }
}
The original_marker is replaced with the actual target density function during processing.

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Wrapped Marker Density Function

A marker type that indicates a reference to the wrapped (modified) density function. Java Interface: 
public class WrappedMarkerDensityFunction implements MarkerFunction {
    // No computation - throws exception if called
    @Override
    public double compute(FunctionContext context) {
        throw new IllegalStateException("Marker density function should never be computed!");
    }
}
Source: WrappedMarkerDensityFunction.java:8-15 Purpose:
  • References the already-modified density function
  • Allows chaining multiple modifications
  • Resolved before execution
JSON Format: 
{
  "type": "lithostitched:wrapped_marker"
}
Usage in Modifier Chains: 
{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "modifier": {
    "type": "minecraft:mul",
    "argument1": {
      "type": "lithostitched:wrapped_marker"
    },
    "argument2": {
      "type": "minecraft:constant",
      "argument": 1.5
    }
  }
}
If this is the second modifier on the same density function, wrapped_marker references the result of the first modification.

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Marker Function Interface

Base interface for marker density functions. Java Interface: 
public interface MarkerFunction extends DensityFunction.SimpleFunction {
    @Override
    default double compute(FunctionContext context) {
        throw new IllegalStateException("Marker density function should never be computed!");
    }

    @Override
    default double minValue() {
        return 0;
    }

    @Override
    default double maxValue() {
        return 0;
    }
}
Source: MarkerFunction.java:5-20 Characteristics:
  • Cannot be computed directly
  • Returns 0 for min/max values
  • Acts as a symbolic reference
  • Resolved during density function graph building

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How Markers Work

Markers enable safe reference to density functions that are being modified:

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Without Markers

{
  "type": "minecraft:add",
  "argument1": {
    "type": "minecraft:noise",
    "noise": "minecraft:offset"
  },
  "argument2": {
    "type": "minecraft:constant",
    "argument": 0.5
  }
}
This creates a new density function but doesn’t preserve the original.

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With Markers

{
  "type": "minecraft:add",
  "argument1": {
    "type": "lithostitched:original_marker"
  },
  "argument2": {
    "type": "minecraft:constant",
    "argument": 0.5
  }
}
The marker is replaced with the actual target function, creating a MergedDensityFunction that maintains both original and modified versions.

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Practical Examples

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Amplify Terrain

{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "modifier": {
    "type": "minecraft:mul",
    "argument1": {
      "type": "lithostitched:original_marker"
    },
    "argument2": {
      "type": "minecraft:constant",
      "argument": 2.0
    }
  }
}
Doubles the terrain height variation.

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Add Noise Layer

{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "modifier": {
    "type": "minecraft:add",
    "argument1": {
      "type": "lithostitched:original_marker"
    },
    "argument2": {
      "type": "minecraft:noise",
      "noise": "mymod:terrain_detail",
      "xz_scale": 1.0,
      "y_scale": 1.0
    }
  }
}
Adds additional noise variation to the base terrain.

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Smooth Terrain

{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "modifier": {
    "type": "minecraft:mul",
    "argument1": {
      "type": "lithostitched:original_marker"
    },
    "argument2": {
      "type": "minecraft:constant",
      "argument": 0.5
    }
  }
}
Reduces terrain variation by half.

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Blend Two Functions

{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "modifier": {
    "type": "minecraft:blend_density",
    "argument": {
      "type": "minecraft:add",
      "argument1": {
        "type": "minecraft:mul",
        "argument1": {
          "type": "lithostitched:original_marker"
        },
        "argument2": {
          "type": "minecraft:constant",
          "argument": 0.7
        }
      },
      "argument2": {
        "type": "minecraft:mul",
        "argument1": {
          "type": "minecraft:noise",
          "noise": "mymod:alternative_terrain",
          "xz_scale": 0.25,
          "y_scale": 1.0
        },
        "argument2": {
          "type": "minecraft:constant",
          "argument": 0.3
        }
      }
    }
  }
}
Blends 70% original terrain with 30% custom noise.

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Chain Modifications

First Modifier: 
{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "priority": 100,
  "modifier": {
    "type": "minecraft:mul",
    "argument1": {
      "type": "lithostitched:original_marker"
    },
    "argument2": {
      "type": "minecraft:constant",
      "argument": 1.5
    }
  }
}
Second Modifier: 
{
  "type": "lithostitched:modify_density_function",
  "target": "minecraft:overworld/base_3d_noise",
  "priority": 200,
  "modifier": {
    "type": "minecraft:add",
    "argument1": {
      "type": "lithostitched:wrapped_marker"
    },
    "argument2": {
      "type": "minecraft:noise",
      "noise": "mymod:detail",
      "xz_scale": 2.0,
      "y_scale": 1.0
    }
  }
}
The second modifier uses wrapped_marker to reference the result of the first (amplified terrain), then adds detail noise.

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Technical Details

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Recursive Unwrapping

The unwrappedOriginal method recursively unwraps MergedDensityFunction layers: 
private static DensityFunction unwrappedOriginal(DensityFunction df) {
    return df instanceof MergedDensityFunction merged 
        ? unwrappedOriginal(merged.original()) 
        : df;
}
This ensures you always get the true original function, no matter how many modifications have been applied.

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Marker Resolution

Markers are resolved during worldgen modifier processing:
  1. Modifier specifies a target density function
  2. System finds the target in the noise router
  3. original_marker is replaced with the current target function
  4. wrapped_marker is replaced with the previous modification result (if any)
  5. A new MergedDensityFunction is created with original, wrapped, and full references

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Registry Information

Custom Density Function Types:
  • lithostitched:merged - Merged function wrapper
  • lithostitched:original_marker - Original function marker
  • lithostitched:wrapped_marker - Wrapped function marker
Marker functions should never appear in final density function graphs. If you encounter “Marker density function should never be computed” errors, a marker was not properly resolved during modifier processing.

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See Also

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