3dtrial/tinyrender1_perspective/main.go

package main

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

const (
	Width      = 512
	Height     = 512
	FOV        = 70
	NearClip   = 0.1
	FarClip    = 5 // Because the head is so small and close
	ObjectFile = "head.obj"
	Repeat     = 1 // Because I want to see an animation
)

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

// However flag works... idk
var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
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 fov = flag.Float64("fov", 90, "Field of view")

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", ObjectFile)

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

	log.Printf("Running render")

	halfwidth := float32(fb.Width / 2)
	halfheight := float32(fb.Height / 2)

	var projection Mat44f
	var worldToCamera Mat44f
	projection.SetProjection(float32(*fov), NearClip, FarClip)
	worldToCamera.SetIdentity()
	worldToCamera.Set(0, 3, float32(*xofs)) // Let user decide how to offset x
	worldToCamera.Set(2, 3, float32(*zofs)) // Get farther away from the face (user)

	var x [3]int
	var y [3]int
	var c [3]uint
	var hi = int(fb.Height - 1)
	for range Repeat {
		for _, f := range o.Faces {
			// Precompute perspective for vertices to save time. Notice Z
			// is not considered: is this orthographic projection? Yeah probably...
			for i := range 3 { // Triangles, bro
				// The ONLY difference between this and the non-perspective is this multiplication.
				// Is this really all that's required?
				fp := worldToCamera.MultiplyPoint3(f[i])
				fp = projection.MultiplyPoint3(fp)
				//log.Print(uint16(fp.Z * 65535))
				x[i] = int((fp.X + 1) * halfwidth)
				y[i] = hi - int((fp.Y+1)*halfheight)
				c[i] = 0xFFFFFF
				//c[i] = Col2Uint(byte(0xFF*fp.Z), byte(0xFF*fp.Z), byte(0xFF*fp.Z))
			}
			Bresenham2(&fb, c[0], x[0], y[0], x[1], y[1])
			Bresenham2(&fb, c[1], x[1], y[1], x[2], y[2])
			Bresenham2(&fb, c[2], x[2], y[2], x[0], y[0])
		}
	}

	log.Printf("Exporting ppm to stdout")
	fmt.Print(fb.ExportPPM())

	log.Printf("Program end")
}