Initial commit: RegionIO Minecraft server core (26.1.2/protocol 775)

Vanilla-faithful overworld generator (final_density + multi-noise biomes),
full connection lifecycle (status/login/configuration/play), chunk streaming,
creative block editing, and the protocol/nbt/registry infrastructure.

internal/worldgen/normal_noise.go

@@ -0,0 +1,49 @@
+package worldgen
+
+// normalInputFactor is NormalNoise.INPUT_FACTOR, the frequency offset applied
+// to the second Perlin field so the two octave stacks don't align.
+const normalInputFactor = 1.0181268882175227
+
+// NormalNoise combines two PerlinNoise fields, scaled so the result has a
+// normalized deviation. This is the noise type referenced by density functions.
+type NormalNoise struct {
+	first       *PerlinNoise
+	second      *PerlinNoise
+	valueFactor float64
+	maxValue    float64
+}
+
+// NewNormalNoise builds a NormalNoise from the same parameters vanilla uses:
+// two PerlinNoise stacks drawn sequentially from r, plus a value factor derived
+// from the span of non-zero amplitudes.
+func NewNormalNoise(r RandomSource, firstOctave int, amplitudes []float64) *NormalNoise {
+	n := &NormalNoise{
+		first:  NewPerlinNoise(r, firstOctave, amplitudes),
+		second: NewPerlinNoise(r, firstOctave, amplitudes),
+	}
+
+	min, max := len(amplitudes), 0
+	for i, a := range amplitudes {
+		if a != 0 {
+			if i < min {
+				min = i
+			}
+			if i > max {
+				max = i
+			}
+		}
+	}
+	expectedDeviation := 0.1 * (1.0 + 1.0/float64(max-min+1))
+	n.valueFactor = (1.0 / 6.0) / expectedDeviation
+	n.maxValue = (n.first.MaxValue() + n.second.MaxValue()) * n.valueFactor
+	return n
+}
+
+// GetValue samples the combined noise at (x, y, z).
+func (n *NormalNoise) GetValue(x, y, z float64) float64 {
+	return (n.first.GetValue(x, y, z) +
+		n.second.GetValue(x*normalInputFactor, y*normalInputFactor, z*normalInputFactor)) * n.valueFactor
+}
+
+// MaxValue returns the theoretical maximum magnitude.
+func (n *NormalNoise) MaxValue() float64 { return n.maxValue }