stl2gltf/convert_glb.go

package stl2gltf

import (
	"encoding/binary"
	"encoding/json"
	"log"
	"os"
)

func ConvertGLB(stl STL, outFile string) {
	// buf
	indexBuf := make([]byte, 0)
	normalBuf := make([]byte, 0)
	positionBuf := make([]byte, 0)

	// padding each buffer part
	padding := func(buf []byte) []byte {
		for len(buf)%4 != 0 {
			buf = append(buf, 0x00)
		}
		return buf
	}

	// positions to byte
	for i := range stl.TriangleNum {
		t := stl.Triangles[i]
		positionBuf = append(positionBuf, t.Position...)
	}
	positionBuf = padding(positionBuf)

	// normals to byte
	for i := range stl.TriangleNum {
		t := stl.Triangles[i]
		// each position, write 3 times
		normalBuf = append(normalBuf, t.Normal...)
		normalBuf = append(normalBuf, t.Normal...)
		normalBuf = append(normalBuf, t.Normal...)
	}
	normalBuf = padding(normalBuf)
	// indices to byte
	for i := range stl.TriangleNum * 3 {
		buf := make([]byte, 4)
		binary.LittleEndian.PutUint32(buf, uint32(i))
		indexBuf = append(indexBuf, buf...)
	}
	indexBuf = padding(indexBuf)

	log.Println("positions: ", len(positionBuf), " normals: ", len(normalBuf), " indices: ", len(indexBuf))

	// concat
	allData := make([]byte, 0)
	allData = append(allData, indexBuf...)    // Indices: 0
	allData = append(allData, normalBuf...)   // attributes["NORMAL"] = 1
	allData = append(allData, positionBuf...) // attributes["POSITION"] = 2

	// base := base64.StdEncoding.EncodeToString(allData)
	attributes := make(map[string]int, 0)
	attributes["NORMAL"] = 1
	attributes["POSITION"] = 2

	gltf := GLTF{
		Asset:  Asset{Version: "2.0"},
		Scenes: []Scene{{Nodes: []int{0}}},
		Nodes:  []Node{{Mesh: 0}},
		Meshes: []Mesh{{Primitives: []Primitive{{Attributes: attributes, Indices: 0, Mode: 4}}}},
		// ByteLength not length after base64
		Buffers: []Buffer{{ByteLength: len(allData)}},
		BufferViews: []BufferView{
			// index
			{
				Buffer:     0,
				ByteOffset: 0,
				ByteLength: len(indexBuf),
				Target:     34963, // ELEMENT_ARRAY_BUFFER  float   indices
			},
			// normal
			{
				Buffer:     0,
				ByteOffset: len(indexBuf),
				ByteLength: len(normalBuf),
				Target:     34962, // ARRAY_BUFFER    int   vertex
			},
			// position
			{
				Buffer:     0,
				ByteOffset: len(indexBuf) + len(normalBuf),
				ByteLength: len(positionBuf),
				Target:     34962, // ARRAY_BUFFER    int   vertex
			},
		},
		Accessors: []Accessor{
			{
				BufferView:    0,
				ByteOffset:    0,
				ComponentType: 5125,                // uint ;      5124 int will loss model parts
				Type:          "SCALAR",            // index
				Count:         stl.TriangleNum * 3, // 1 index : 1 position
			},
			{
				BufferView:    1,
				ByteOffset:    0,
				ComponentType: 5126, // float
				Type:          "VEC3",
				Count:         stl.TriangleNum * 3, // 1 normal : 1 position
				Max:           []float32{1, 1, 1},  // or cal from stl data
				Min:           []float32{-1, -1, -1},
			},
			{
				BufferView:    2,
				ByteOffset:    0,
				ComponentType: 5126, // float
				Type:          "VEC3",
				Count:         len(positionBuf) / 12, // xyz = 4x3; or stl.TriangleNum * 3
				Max:           stl.Max,               // cal from stl data
				Min:           stl.Min,
			},
		},
	}

	// 生成glb
	outBuf := make([]byte, 0)

	jsonChunkBuf := make([]byte, 0)

	jsonData, err := json.Marshal(gltf)
	if err != nil {
		log.Println("marshal error: ", err.Error())
		return
	}
	jsonChunkBuf = binary.LittleEndian.AppendUint32(jsonChunkBuf, uint32(len(jsonData)))
	jsonChunkBuf = binary.LittleEndian.AppendUint32(jsonChunkBuf, uint32(0x4E4F534A))
	jsonChunkBuf = append(jsonChunkBuf, jsonData...)

	binChunkBuf := make([]byte, 0)
	binChunkBuf = binary.LittleEndian.AppendUint32(binChunkBuf, uint32(len(allData)))
	binChunkBuf = binary.LittleEndian.AppendUint32(binChunkBuf, uint32(0x004E4942))
	binChunkBuf = append(binChunkBuf, allData...)

	outBuf = binary.LittleEndian.AppendUint32(outBuf, uint32(0x46546C67))
	outBuf = binary.LittleEndian.AppendUint32(outBuf, uint32(2))
	outBuf = binary.LittleEndian.AppendUint32(outBuf, uint32(12+len(jsonChunkBuf)+len(binChunkBuf)))

	outBuf = append(outBuf, jsonChunkBuf...)
	outBuf = append(outBuf, binChunkBuf...)

	// output
	os.Remove(outFile)
	f, err := os.OpenFile(outFile, os.O_CREATE, os.ModePerm)
	if err != nil {
		log.Println("write file error: ", err.Error())
		return
	}
	defer f.Close()
	f.Write(outBuf)
}