readbinary.go

package stl

// This file defines reading functions for the STL binary format.

import (
	"encoding/binary"
	"fmt"
	"io"
	"math"
)

const binaryHeaderSize = 84
const binaryTriangleSize = 50

func readAllBinary(r io.Reader, sw Writer) (err error) {
	var header [binaryHeaderSize]byte
	n, readErr := r.Read(header[:])
	if readErr == io.EOF && n != binaryHeaderSize {
		err = ErrIncompleteBinaryHeader
		return
	} else if readErr != nil {
		err = readErr
		return
	}

	sw.SetBinaryHeader(header[0 : binaryHeaderSize-4])
	sw.SetName(extractASCIIString(header[0 : binaryHeaderSize-4]))
	triangleCount := triangleCountFromBinaryHeader(header[:])
	sw.SetTriangleCount(triangleCount)

	var t Triangle
	for i := uint32(0); i < triangleCount; i++ {
		readErr = readTriangleBinary(r, &t)
		if readErr != nil {
			err = fmt.Errorf("while reading triangle no. %d at byte %d: %s", i, binaryHeaderSize+i*binaryTriangleSize, readErr.Error())
			return
		}
		sw.AppendTriangle(t)
	}

	return
}

func triangleCountFromBinaryHeader(header []byte) uint32 {
	return binary.LittleEndian.Uint32(header[binaryHeaderSize-4 : binaryHeaderSize])
}

func readTriangleBinary(r io.Reader, t *Triangle) error {
	tbuf := make([]byte, binaryTriangleSize)
	n := 0
	for n < binaryTriangleSize {
		l, readErr := r.Read(tbuf[n:])
		n += l
		if readErr != nil {
			if readErr == io.EOF {
				return ErrUnexpectedEOF
			}
			return readErr
		}
	}

	offset := 0
	readBinaryPoint(tbuf, &offset, &(t.Normal))
	readBinaryPoint(tbuf, &offset, &(t.Vertices[0]))
	readBinaryPoint(tbuf, &offset, &(t.Vertices[1]))
	readBinaryPoint(tbuf, &offset, &(t.Vertices[2]))
	t.Attributes = readBinaryUint16(tbuf, &offset)
	return nil
}

func readBinaryPoint(buf []byte, offset *int, p *Vec3) {
	p[0] = readBinaryFloat32(buf, offset)
	p[1] = readBinaryFloat32(buf, offset)
	p[2] = readBinaryFloat32(buf, offset)
}

func readBinaryFloat32(buf []byte, offset *int) float32 {
	v := binary.LittleEndian.Uint32(buf[*offset : (*offset)+4])
	*offset += 4
	return math.Float32frombits(v)
}

func readBinaryUint16(buf []byte, offset *int) uint16 {
	v := binary.LittleEndian.Uint16(buf[*offset : (*offset)+2])
	*offset += 2
	return v
}