Look ma, no Bukkit API in the core package

common/src/main/java/com/dfsek/terra/math/BlankFunction.java

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+package com.dfsek.terra.math;
+
+import parsii.eval.Expression;
+import parsii.eval.Function;
+
+import java.util.List;
+
+public class BlankFunction implements Function {
+    private final int args;
+
+    public BlankFunction(int args) {
+        this.args = args;
+    }
+
+    @Override
+    public int getNumberOfArguments() {
+        return args;
+    }
+
+    @Override
+    public double eval(List<Expression> list) {
+        return 0;
+    }
+
+    @Override
+    public boolean isNaturalFunction() {
+        return true;
+    }
+}

common/src/main/java/com/dfsek/terra/math/MathUtil.java

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+package com.dfsek.terra.math;
+
+import com.dfsek.terra.generation.Sampler;
+
+public final class MathUtil {
+    private static final double CONST = 0.55;
+
+    public static double derivative(Sampler sampler, double x, double y, double z) {
+        double baseSample = sampler.sample(x, y, z);
+
+        double xVal1 = (sampler.sample(x + CONST, y, z) - baseSample) / CONST;
+        double xVal2 = (sampler.sample(x - CONST, y, z) - baseSample) / CONST;
+        double zVal1 = (sampler.sample(x, y, z + CONST) - baseSample) / CONST;
+        double zVal2 = (sampler.sample(x, y, z - CONST) - baseSample) / CONST;
+        double yVal1 = (sampler.sample(x, y + CONST, z) - baseSample) / CONST;
+        double yVal2 = (sampler.sample(x, y - CONST, z) - baseSample) / CONST;
+
+        return Math.sqrt(((xVal2 - xVal1) * (xVal2 - xVal1)) + ((zVal2 - zVal1) * (zVal2 - zVal1)) + ((yVal2 - yVal1) * (yVal2 - yVal1)));
+    }
+}

common/src/main/java/com/dfsek/terra/math/NoiseFunction.java

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+package com.dfsek.terra.math;
+
+import parsii.eval.Function;
+
+public interface NoiseFunction extends Function {
+}

common/src/main/java/com/dfsek/terra/math/NoiseFunction2.java

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+package com.dfsek.terra.math;
+
+import com.dfsek.terra.api.gaea.math.FastNoiseLite;
+import com.dfsek.terra.generation.config.NoiseBuilder;
+import com.dfsek.terra.util.hash.HashMapDoubleDouble;
+import parsii.eval.Expression;
+
+import java.util.List;
+
+public class NoiseFunction2 implements NoiseFunction {
+    private final FastNoiseLite gen;
+    private final Cache cache = new Cache();
+
+    public NoiseFunction2(long seed, NoiseBuilder builder) {
+        this.gen = builder.build((int) seed);
+    }
+
+    @Override
+    public int getNumberOfArguments() {
+        return 2;
+    }
+
+    @Override
+    public double eval(List<Expression> list) {
+        return cache.get(gen, list.get(0).evaluate(), list.get(1).evaluate());
+    }
+
+    /**
+     * Evaluate without cache. For testing.
+     *
+     * @param list Parameters.
+     * @return Result.
+     */
+    public double evalNoCache(List<Expression> list) {
+        return gen.getNoise(list.get(0).evaluate(), list.get(1).evaluate());
+    }
+
+    @Override
+    public boolean isNaturalFunction() {
+        return true;
+    }
+
+    private static class Cache extends HashMapDoubleDouble {
+        private static final long serialVersionUID = 8915092734723467010L;
+        private static final int cacheSize = 384;
+
+        public double get(FastNoiseLite noise, double x, double z) {
+            double xx = x >= 0 ? x * 2 : x * -2 - 1;
+            double zz = z >= 0 ? z * 2 : z * -2 - 1;
+            double key = (xx >= zz) ? (xx * xx + xx + zz) : (zz * zz + xx);
+            double value = this.get(key);
+            if(this.size() > cacheSize) {
+                this.clear();
+            }
+            return (value == 4.9E-324D ? addAndReturn(noise.getNoise(x, z), key) : value);
+        }
+
+        private double addAndReturn(double value, double key) {
+            this.put(key, value);
+            return value;
+        }
+    }
+}

common/src/main/java/com/dfsek/terra/math/NoiseFunction3.java

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+package com.dfsek.terra.math;
+
+import com.dfsek.terra.api.gaea.math.FastNoiseLite;
+import com.dfsek.terra.generation.config.NoiseBuilder;
+import parsii.eval.Expression;
+
+import java.util.List;
+
+public class NoiseFunction3 implements NoiseFunction {
+    private final FastNoiseLite gen;
+
+    public NoiseFunction3(long seed, NoiseBuilder builder) {
+        this.gen = builder.build((int) seed);
+    }
+
+    @Override
+    public int getNumberOfArguments() {
+        return 3;
+    }
+
+    @Override
+    public double eval(List<Expression> list) {
+        return gen.getNoise(list.get(0).evaluate(), list.get(1).evaluate(), list.get(2).evaluate());
+    }
+
+    @Override
+    public boolean isNaturalFunction() {
+        return true;
+    }
+}

common/src/main/java/com/dfsek/terra/math/RandomFunction.java

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+package com.dfsek.terra.math;
+
+import com.dfsek.terra.api.gaea.util.FastRandom;
+import parsii.eval.Expression;
+import parsii.eval.Function;
+
+import java.util.List;
+
+/**
+ * Provides access to a PRNG ({@link com.dfsek.terra.api.gaea.util.FastRandom})
+ * <p>
+ * Takes 1 argument, which sets the seed
+ */
+public class RandomFunction implements Function {
+    @Override
+    public int getNumberOfArguments() {
+        return 1;
+    }
+
+    @Override
+    public double eval(List<Expression> list) {
+        long seed = (long) list.get(0).evaluate();
+        return new FastRandom(seed).nextDouble();
+    }
+
+    @Override
+    public boolean isNaturalFunction() {
+        return true;
+    }
+}