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/world/terrain.go

@@ -0,0 +1,88 @@
+package world
+
+import (
+	"sync"
+
+	"regionio/internal/worldgen"
+)
+
+// SeaLevel is the water surface height for generated terrain.
+const SeaLevel = 63
+
+// NewTerrainGenerator returns a chunk generator backed by a density function.
+// The density tree is built once (shared, read-only noise state) and sampled
+// per block.
+func NewTerrainGenerator(seed int64) Generator {
+	density := worldgen.SimpleTerrain(seed)
+	return func(cx, cz int32) *Chunk {
+		return generateFromDensity(density, cx, cz)
+	}
+}
+
+// generateFromDensity fills a chunk by sampling the density function (>0 is
+// solid). The per-column sampling is the expensive part and is run in parallel
+// across the 16 x-rows; chunk assembly is sequential to avoid racing on lazy
+// section allocation. Sampling the density only reads shared noise state, so it
+// is safe to run concurrently.
+func generateFromDensity(d worldgen.DensityFunction, cx, cz int32) *Chunk {
+	c := NewChunk(cx, cz, BiomePlains)
+
+	var columns [16][16][WorldHeight]uint16
+	var wg sync.WaitGroup
+	for lx := 0; lx < 16; lx++ {
+		wg.Add(1)
+		go func(lx int) {
+			defer wg.Done()
+			for lz := 0; lz < 16; lz++ {
+				wx := float64(int(cx)*16 + lx)
+				wz := float64(int(cz)*16 + lz)
+				computeColumn(d, wx, wz, &columns[lx][lz])
+			}
+		}(lx)
+	}
+	wg.Wait()
+
+	for lx := 0; lx < 16; lx++ {
+		for lz := 0; lz < 16; lz++ {
+			col := &columns[lx][lz]
+			for i := 0; i < WorldHeight; i++ {
+				if s := col[i]; s != StateAir {
+					c.SetBlock(lx, MinY+i, lz, s)
+				}
+			}
+		}
+	}
+	return c
+}
+
+// computeColumn fills out with the block state for each Y in one column.
+func computeColumn(d worldgen.DensityFunction, wx, wz float64, out *[WorldHeight]uint16) {
+	var solid [WorldHeight]bool
+	top := -1
+	for i := 0; i < WorldHeight; i++ {
+		y := MinY + i
+		if d.Compute(worldgen.FunctionContext{X: wx, Y: float64(y), Z: wz}) > 0 {
+			solid[i] = true
+			top = i
+		}
+	}
+
+	for i := 0; i < WorldHeight; i++ {
+		y := MinY + i
+		switch {
+		case y == MinY:
+			out[i] = StateBedrock
+		case solid[i]:
+			switch {
+			case i == top && y >= SeaLevel:
+				out[i] = StateGrass
+			case i > top-4:
+				out[i] = StateDirt
+			default:
+				out[i] = StateStone
+			}
+		case y < SeaLevel:
+			out[i] = StateWater
+		}
+	}
+}