Add StructureManager and NBT template loader for large structures

cmd/genblocks/main.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+func main() {
+	f, err := os.Open("generated/reports/blocks.json")
+	if err != nil {
+		panic(err)
+	}
+	var data map[string]struct {
+		States []struct {
+			ID      int  `json:"id"`
+			Default bool `json:"default"`
+		} `json:"states"`
+	}
+	if err := json.NewDecoder(f).Decode(&data); err != nil {
+		panic(err)
+	}
+
+	out, _ := os.Create("internal/worldgen/generated_blocks.go")
+	fmt.Fprintln(out, "package worldgen")
+	fmt.Fprintln(out, "")
+	fmt.Fprintln(out, "// defaultBlockIDs maps block names to their default state ID.")
+	fmt.Fprintln(out, "var defaultBlockIDs = map[string]uint16{")
+
+	for name, block := range data {
+		for _, state := range block.States {
+			if state.Default {
+				fmt.Fprintf(out, "\t%q: %d,\n", name, state.ID)
+			}
+		}
+	}
+	fmt.Fprintln(out, "}")
+	out.Close()
+}

internal/world/vanilla.go

@@ -111,7 +111,7 @@ func generateVanilla(od *worldgen.OverworldDensity, seed int64, cx, cz int32) *C
 		}
 	}
 	fillBiomes3D(c, od, s2D, baseX, baseZ)
-	decorate(c, cx, cz, seed, &surfTop, &grass, &biomeName)
+	decorate(c, od, cx, cz, seed, &surfTop, &grass, &biomeName)
 	return c
 }
 
@@ -300,7 +300,7 @@ func bedrockAt(rng chunkRand, d int) bool {
 // decorate places simple oak trees on grassy columns. Trunks are kept two
 // blocks inside the chunk so the radius-2 canopy never crosses into a neighbour
 // (avoiding cross-chunk coordination); placement is deterministic per chunk.
-func decorate(c *Chunk, cx, cz int32, seed int64, surfTop *[16][16]int, grass *[16][16]bool, biomeName *[16][16]string) {
+func decorate(c *Chunk, od *worldgen.OverworldDensity, cx, cz int32, seed int64, surfTop *[16][16]int, grass *[16][16]bool, biomeName *[16][16]string) {
 	r := newChunkRand(cx, cz, seed)
 
 	placeOres(c, &r)
@@ -318,6 +318,9 @@ func decorate(c *Chunk, cx, cz int32, seed int64, surfTop *[16][16]int, grass *[
 		baseY := MinY + surfTop[lx][lz] + 1
 		placeOak(c, lx, baseY, lz, &r)
 	}
+
+	// Place large structures like villages and strongholds
+	worldgen.PlaceStructures(c, od, cx, cz, seed, surfTop, biomeName)
 }
 
 func placeOak(c *Chunk, lx, baseY, lz int, r *chunkRand) {

internal/worldgen/structure.go

@@ -0,0 +1,163 @@
+package worldgen
+
+import (
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"os"
+
+	"regionio/internal/nbt"
+)
+
+type ChunkWriter interface {
+	SetBlock(lx, y, lz int, state uint16)
+	GetBlock(lx, y, lz int) uint16
+}
+
+// Template represents a loaded NBT structure.
+type Template struct {
+	Size    [3]int
+	Blocks  []TemplateBlock
+	Palette []uint16 // mapped to global block IDs
+}
+
+type TemplateBlock struct {
+	Pos   [3]int
+	State uint16
+}
+
+// LoadTemplate reads a vanilla structure NBT file.
+func LoadTemplate(path string) (*Template, error) {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	
+	// NBT files are usually gzipped.
+	var r io.Reader = bytes.NewReader(b)
+	if len(b) >= 2 && b[0] == 0x1f && b[1] == 0x8b {
+		gr, err := gzip.NewReader(r)
+		if err != nil {
+			return nil, err
+		}
+		defer gr.Close()
+		r = gr
+	}
+
+	out, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	_, root, err := nbt.UnmarshalNamed(out)
+	if err != nil {
+		return nil, err
+	}
+
+	comp, ok := root.(*nbt.Compound)
+	if !ok {
+		return nil, fmt.Errorf("root is not a compound")
+	}
+
+	tmpl := &Template{}
+
+	if tag, ok := comp.Get("size"); ok {
+		if sizeList, ok := tag.(nbt.List); ok && len(sizeList.Elems) == 3 {
+			tmpl.Size[0] = int(sizeList.Elems[0].(nbt.Int))
+			tmpl.Size[1] = int(sizeList.Elems[1].(nbt.Int))
+			tmpl.Size[2] = int(sizeList.Elems[2].(nbt.Int))
+		}
+	}
+
+	// Parse palette
+	if tag, ok := comp.Get("palette"); ok {
+		if paletteList, ok := tag.(nbt.List); ok {
+			for _, v := range paletteList.Elems {
+				stateComp, ok := v.(*nbt.Compound)
+				if !ok {
+					continue
+				}
+				nameTag, _ := stateComp.Get("Name")
+				name := string(nameTag.(nbt.String))
+				props := make(map[string]string)
+				
+				if propTag, ok := stateComp.Get("Properties"); ok {
+					if propComp, ok := propTag.(*nbt.Compound); ok {
+						for _, k := range propComp.Keys() {
+							pval, _ := propComp.Get(k)
+							if str, ok := pval.(nbt.String); ok {
+								props[k] = string(str)
+							}
+						}
+					}
+				}
+				id := surfaceBlockID(name, props)
+				if id == 0 && name != "minecraft:air" {
+					// Fallback to default block ID for the name
+					id = defaultBlockIDs[name]
+				}
+				tmpl.Palette = append(tmpl.Palette, id)
+			}
+		}
+	}
+
+	// Parse blocks
+	if tag, ok := comp.Get("blocks"); ok {
+		if blocksList, ok := tag.(nbt.List); ok {
+			for _, v := range blocksList.Elems {
+				blockComp, ok := v.(*nbt.Compound)
+				if !ok {
+					continue
+				}
+				stateTag, _ := blockComp.Get("state")
+				stateIdx := int(stateTag.(nbt.Int))
+				
+				var pos [3]int
+				if posTag, ok := blockComp.Get("pos"); ok {
+					if posList, ok := posTag.(nbt.List); ok && len(posList.Elems) == 3 {
+						pos[0] = int(posList.Elems[0].(nbt.Int))
+						pos[1] = int(posList.Elems[1].(nbt.Int))
+						pos[2] = int(posList.Elems[2].(nbt.Int))
+					}
+				}
+
+				if stateIdx >= 0 && stateIdx < len(tmpl.Palette) {
+					state := tmpl.Palette[stateIdx]
+					tmpl.Blocks = append(tmpl.Blocks, TemplateBlock{
+						Pos:   pos,
+						State: state,
+					})
+				}
+			}
+		}
+	}
+
+	return tmpl, nil
+}
+
+// Place applies the template blocks to the ChunkWriter if they fall within the given chunk boundaries.
+// cx, cz are the chunk coordinates we are currently generating.
+// originX, originY, originZ is where the [0,0,0] of the template is placed in the world.
+func (t *Template) Place(cw ChunkWriter, cx, cz int32, originX, originY, originZ int) {
+	minX := int(cx) * 16
+	minZ := int(cz) * 16
+	maxX := minX + 15
+	maxZ := minZ + 15
+
+	for _, b := range t.Blocks {
+		wx := originX + b.Pos[0]
+		wy := originY + b.Pos[1]
+		wz := originZ + b.Pos[2]
+
+		if wx >= minX && wx <= maxX && wz >= minZ && wz <= maxZ {
+			lx := wx - minX
+			lz := wz - minZ
+			// Only place if not air, or if you want structures to hollow out space, place air too.
+			// Jigsaw structures use structure_void to mean "don't overwrite", and air to mean "overwrite with air".
+			// Since we fallback to 0 for unknown blocks, we need to be careful.
+			// For now, place everything.
+			cw.SetBlock(lx, wy, lz, b.State)
+		}
+	}
+}

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)
+				}
+			}
+		}
+	}
+}

internal/worldgen/template_cache.go

@@ -0,0 +1,18 @@
+package worldgen
+
+import "sync"
+
+var (
+	templates     = make(map[string]*Template)
+	templatesOnce sync.Once
+)
+
+// GetTemplate loads and caches an NBT template from disk.
+func GetTemplate(name string) *Template {
+	templatesOnce.Do(func() {
+		// Preload some known templates on first use
+		t1, _ := LoadTemplate("internal/worldgen/data/structure/village/plains/houses/plains_small_house_1.nbt")
+		templates["plains_small_house_1"] = t1
+	})
+	return templates[name]
+}

scratch.go

@@ -1,17 +1,13 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
-	"os"
+	"regionio/internal/worldgen"
 )
 
 func main() {
-	f, _ := os.Open("generated/reports/blocks.json")
-	var data map[string]interface{}
-	json.NewDecoder(f).Decode(&data)
-
-	glowstone := data["minecraft:glowstone"]
-	b, _ := json.MarshalIndent(glowstone, "", "  ")
-	fmt.Println("glowstone:", string(b))
+	tmpl, _ := worldgen.LoadTemplate("internal/worldgen/data/structure/village/plains/houses/plains_small_house_1.nbt")
+	for i, b := range tmpl.Palette {
+		fmt.Printf("Palette[%d] = %d\n", i, b)
+	}
 }