stl2gltf/convert.go

package stl2gltf

import (
	"encoding/base64"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"log"
	"os"
)

func Convert(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 {
		log.Println("padding: ", len(buf)%4)
		for len(buf)%4 != 0 {
			log.Println("padding")
			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(len(positionBuf), len(normalBuf), 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{{Uri: fmt.Sprintf("data:application/gltf-buffer;base64,%s", base), 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,
			},
		},
	}
	// or not indent
	data, err := json.MarshalIndent(gltf, " ", " ")
	if err != nil {
		log.Println("marshal error: ", err.Error())
		return
	}
	// 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(data)
}