3dtrial/tinyrender2/obj.go

package main

// This reads obj files?
import (
	"bufio"
	"fmt"
	"io"
	"log"
	"math"
	"strings"
)

type Vec3f struct {
	X, Y, Z float32
}

type Vec2i struct {
	X, Y int
}

type Vec2f struct {
	X, Y float32
}

type Facef [3]Vec3f

type ObjModel struct {
	Vertices []Vec3f
	Faces    []Facef
}

func (vi *Vec2i) ToF() Vec2f {
	return Vec2f{float32(vi.X), float32(vi.Y)}
}

func (v0 *Vec3f) Sub(v1 Vec3f) Vec3f {
	return Vec3f{
		X: v0.X - v1.X,
		Y: v0.Y - v1.Y,
		Z: v0.Z - v1.Z,
	}
}

func (v0 *Vec3f) CrossProduct(v1 Vec3f) Vec3f {
	return Vec3f{
		X: v0.Y*v1.Z - v0.Z*v1.Y,
		Y: v0.Z*v1.X - v0.X*v1.Z,
		Z: v0.X*v1.Y - v0.Y*v1.X,
	}
}

func (v *Vec3f) Normalize() Vec3f {
	l := float32(math.Sqrt(float64(v.MultSimp(v))))
	return Vec3f{
		X: v.X / l,
		Y: v.Y / l,
		Z: v.Z / l,
	}
}

func (v0 *Vec3f) MultSimp(v1 *Vec3f) float32 {
	return v0.X*v1.X + v0.Y*v1.Y + v0.Z*v1.Z
}

// Parse an obj file at the given reader. Only handles v and f right now
func ParseObj(reader io.Reader) (*ObjModel, error) {
	result := ObjModel{
		Vertices: make([]Vec3f, 0),
		Faces:    make([]Facef, 0),
	}
	breader := bufio.NewReader(reader)
	done := false
	for !done {
		// Scan a line
		line, err := breader.ReadString('\n')
		if err != nil {
			if err == io.EOF {
				done = true
			} else {
				log.Printf("NOT EOF ERR?")
				return nil, err
			}
		}
		line = strings.Trim(line, " \t\n\r")
		if len(line) == 0 {
			continue
		}
		// Find the first "item", whatever that is. This also gets rid of comments
		// since we just don't use lines that start with # (no handler
		var t string
		_, err = fmt.Sscan(line, &t)
		if err != nil {
			log.Printf("SSCANF ERR")
			return nil, err
		}
		line = line[len(t):]
		if t == "v" {
			// Read a vertex, should be just three floats
			var vertex Vec3f
			_, err := fmt.Sscan(line, &vertex.X, &vertex.Y, &vertex.Z)
			if err != nil {
				return nil, err
			}
			result.Vertices = append(result.Vertices, vertex)
		} else if t == "f" {
			// Read a face; in our example, it's always three sets.
			// For THIS example, we throw away those other values
			var face Facef
			var vi [3]int
			var ti int
			_, err := fmt.Sscanf(line, "%d/%d/%d %d/%d/%d %d/%d/%d",
				&vi[0], &ti, &ti, &vi[1], &ti, &ti, &vi[2], &ti, &ti)
			if err != nil {
				return nil, err
			}
			for i := range 3 {
				if vi[i] > len(result.Vertices) || vi[i] < 1 {
					return nil, fmt.Errorf("Face vertex index out of bounds: %d", vi[i])
				}
				face[i] = result.Vertices[vi[i]-1]
			}
			result.Faces = append(result.Faces, face)
		}
	}
	return &result, nil
}