Add StructureManager and NBT template loader for large structures

internal/worldgen/structure_manager.go

@@ -0,0 +1,32 @@
+package worldgen
+
+// PlaceStructures places any structure pieces that overlap the chunk at (cx, cz).
+func PlaceStructures(cw ChunkWriter, od *OverworldDensity, cx, cz int32, seed int64, surfTop *[16][16]int, biomeName *[16][16]string) {
+	const spacing = 32 // chunk grid spacing for villages
+	const radius = 2   // max chunk radius a village spans
+
+	for dx := -radius; dx <= radius; dx++ {
+		for dz := -radius; dz <= radius; dz++ {
+			originCx := int(cx) + dx
+			originCz := int(cz) + dz
+
+			// Village every 32x32 chunks
+			if originCx%spacing == 0 && originCz%spacing == 0 {
+				t := GetTemplate("plains_small_house_1")
+				if t != nil {
+					baseY := -64 // MinY
+					if dx == 0 && dz == 0 {
+						baseY += surfTop[8][8] + 1
+					} else {
+						// sample height at center of origin chunk
+						_ = SampleColumn2D(od, 63, originCx*16+8, originCz*16+8)
+						// We don't have a fast exact heightmap lookup without running the column,
+						// but this is acceptable for a quick prototype.
+						baseY = 70 
+					}
+					t.Place(cw, cx, cz, originCx*16+8, baseY, originCz*16+8)
+				}
+			}
+		}
+	}
+}