3dtrial/tinyrender4/main.go

package main

import (
	"flag"
	"fmt"
	"image"
	"log"
	//"math"
	//"math/rand"
	"os"
	"runtime/pprof" // For performance profiling (unnecessary)

	_ "image/jpeg"
)

const (
	Width       = 512
	Height      = 512
	NearClip    = 0.1
	FarClip     = 5 // Because the head is so small and close
	ObjectFile  = "head.obj"
	TextureFile = "../head.jpg"
)

func must(err error) {
	if err != nil {
		panic(err)
	}
}

// However flag works... idk
var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
var dozbuf = flag.Bool("zbuffer", false, "Write zbuffer instead of image")
var p6file = flag.String("p6file", "", "Output binary ppm to given file instead")
var fov = flag.Float64("fov", 90, "Horizontal FOV in degrees")
var xofs = flag.Float64("xofs", 0, "Offset image by x")
var zofs = flag.Float64("zofs", -1.5, "Offset image by z (should be negative)")
var repeat = flag.Int("repeat", 60, "Amount of times to repeat render")

// var zcuthigh = flag.Float64("zcuthigh", math.MaxFloat32, "High cutoff for z (values above this will be removed)")
// var zcutlow = flag.Float64("zcutlow", -math.MaxFloat32, "Low cutoff for z (values below are removed)")

func main() {
	log.Printf("Program start")

	// Little section for doing cpu profiling. I guess that's all you have to do?
	flag.Parse()
	if *cpuprofile != "" {
		log.Printf("CPU profiling requested, write to %s", *cpuprofile)
		f, err := os.Create(*cpuprofile)
		must(err)
		defer f.Close()
		err = pprof.StartCPUProfile(f)
		must(err)
		defer pprof.StopCPUProfile()
	}

	fb := NewFramebuffer(Width, Height)

	log.Printf("Loading obj %s, texture %s", ObjectFile, TextureFile)

	of, err := os.Open(ObjectFile)
	must(err)
	defer of.Close()
	o, err := ParseObj(of)
	must(err)

	jf, err := os.Open(TextureFile)
	must(err)
	defer jf.Close()
	timg, _, err := image.Decode(jf)
	must(err)
	texture := NewTexture(timg, 4)

	log.Printf("Running render")

	light := Vec3f{0, 0, -1}

	var projection Mat44f
	var worldToCamera Mat44f
	projection.SetProjection(float32(*fov), NearClip, FarClip)
	worldToCamera.SetTranslation(float32(*xofs), 0, float32(*zofs))

	// Premultiply all the translation/etc matrices. Why do we do world to camera THEN
	// projection? I guess that makes sense actually, oops... projection is the last step.
	screenmat := worldToCamera.Multiply(&projection)
	// light = worldToCamera.MultiplyPoint3(light)
	// light = light.Normalize()

	halfwidth := float32(fb.Width / 2)
	halfheight := float32(fb.Height / 2)
	var sc [3]Vertex
	var hi = float32(fb.Height - 1)
	for range *repeat {
		fb.ResetZBuffer()
		for _, f := range o.Faces {
			// Precompute perspective for vertices to save time. Notice Z
			// is not considered: is this orthographic projection? Yeah probably...
			var fpt [3]Vec3f
			for i := range 3 { // Triangles, bro
				fp := screenmat.MultiplyPoint3(f[i].Pos)
				fpt[i] = worldToCamera.MultiplyPoint3(f[i].Pos)
				sc[i] = f[i]
				sc[i].Pos.X = (fp.X + 1) * halfwidth
				sc[i].Pos.Y = hi - (fp.Y+1)*halfheight
				sc[i].Pos.Z = fp.Z
				// NOTE: WE USE NEGATIVE Z BECAUSE IT'S SUPPOSED TO BE DISTANCE! AS-IS, CLOSER
				// POINTS HAVE HIGHER Z VLAUES
				// sc[i].Pos.Z = -fp.Z // Pull Z value directly. This is fine, our z-buffer is currently float32
			}

			l1 := fpt[2].Sub(fpt[0])
			n := l1.CrossProduct(fpt[1].Sub(fpt[0]))
			n = n.Normalize()
			intensity := n.MultSimp(&light)
			if intensity > 0 {
				Triangle3t(&fb, &texture, intensity, sc[0], sc[1], sc[2])
			}
		}
	}

	if *dozbuf {
		log.Printf("Exporting zbuffer ppm to stdout")
		fmt.Print(fb.ZBuffer_ExportPPM())
	} else {
		if *p6file != "" {
			err := os.WriteFile(*p6file, fb.ExportPPMP6(), 0660)
			must(err)
		} else {
			log.Printf("Exporting ppm to stdout")
			fmt.Print(fb.ExportPPM())
		}
	}

	log.Printf("Program end")
}