Cool perspective

tinyrender1_perspective/.gitignore

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+tinyrender1

tinyrender1_perspective/go.mod

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+module tinyrender1
+
+go 1.22.5
+
+require github.com/udhos/gwob v1.0.0

tinyrender1_perspective/go.sum

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+github.com/udhos/gwob v1.0.0 h1:P9br9SLca7H5Hr/WuEcO9+ViUm+wlQnr4vxpPU6c6ww=
+github.com/udhos/gwob v1.0.0/go.mod h1:xj4qGbkwL1sTPm1V17NfcIhkgG2rjfb8cUv9YIqE6DE=

tinyrender1_perspective/image.go

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+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Convert rgb to uint
+func Col2Uint(r, g, b byte) uint {
+	return (uint(r) << 16) | (uint(g) << 8) | uint(b)
+}
+
+// Convert uint to rgb (in that order)
+func Uint2Col(col uint) (byte, byte, byte) {
+	return byte((col >> 16) & 0xFF), byte((col >> 8) & 0xFF), byte(col & 0xFF)
+}
+
+// Color is in ARGB (alpha not used right now)
+type Framebuffer struct {
+	Data   []uint
+	Width  uint
+	Height uint
+}
+
+// Create a new framebuffer for the given width and height.
+func NewFramebuffer(width uint, height uint) Framebuffer {
+	return Framebuffer{
+		Data:   make([]uint, width*height),
+		Width:  width,
+		Height: height,
+	}
+}
+
+// Sure hope this gets inlined...
+func (fb *Framebuffer) Set(x uint, y uint, color uint) {
+	fb.Data[x+y*fb.Width] = color
+}
+
+func (fb *Framebuffer) SetSafe(x uint, y uint, color uint) {
+	if x >= fb.Width || y >= fb.Height {
+		return
+	}
+	fb.Data[x+y*fb.Width] = color
+}
+
+// Given some image data, return a string that is the ppm of it
+func (fb *Framebuffer) ExportPPM() string {
+	var result strings.Builder
+	result.WriteString(fmt.Sprintf("P3\n%d %d\n255\n", fb.Width, fb.Height))
+	for y := range fb.Height {
+		for x := range fb.Width {
+			r, g, b := Uint2Col(fb.Data[x+y*fb.Width])
+			result.WriteString(fmt.Sprintf("%d %d %d\t", r, g, b))
+		}
+		result.WriteRune('\n')
+	}
+	return result.String()
+}

tinyrender1_perspective/main.go

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+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"runtime/pprof" // For performance profiling (unnecessary)
+)
+
+const (
+	Width      = 512
+	Height     = 512
+	FOV        = 110
+	NearClip   = 0.1
+	FarClip    = 2 // Because the head is so small and close
+	ObjectFile = "head.obj"
+	Repeat     = 1000
+)
+
+func must(err error) {
+	if err != nil {
+		panic(err)
+	}
+}
+
+// However flag works... idk
+var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to file")
+
+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(FOV, NearClip, FarClip)
+	worldToCamera.SetIdentity()
+	worldToCamera.Set(2, 3, -1) // Get farther away from the face
+
+	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)
+				x[i] = int((fp.X + 1) * halfwidth)
+				y[i] = hi - int((fp.Y+1)*halfheight)
+				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")
+}

tinyrender1_perspective/obj.go

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+package main
+
+// This reads obj files?
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"math"
+	"strings"
+)
+
+// These should probably go somewhere else but they're here because they're tied
+// with the object format specification and I don't want a lot of granularity right now
+
+type Vec3f struct {
+	X, Y, Z float32
+}
+
+// A ROW MAJOR matrix
+type Mat44f [16]float32
+
+func (m *Mat44f) Set(x int, y int, val float32) {
+	m[x+y*4] = val
+}
+func (m *Mat44f) Get(x int, y int) float32 {
+	return m[x+y*4]
+}
+func (m *Mat44f) ZeroFill() {
+	for i := range m {
+		m[i] = 0
+	}
+}
+func (m *Mat44f) SetIdentity() {
+	m.ZeroFill()
+	for i := range 4 {
+		m.Set(i, i, 1)
+	}
+}
+
+// Compute the projection matrix, filling the given matrix. FOV is in degrees
+func (m *Mat44f) SetProjection(fov float32, near float32, far float32) {
+	// Projection matrix is
+	// S    0    0    0
+	// 0    S    0    0
+	// 0    0 -f/(f-n) -1
+	// 0    0 -fn/(f-n) 0
+	// where S (scale) is 1 / tan(fov / 2) (assuming fov is radians)
+	m.ZeroFill()
+	scale := float32(1 / math.Tan(float64(fov)*0.5*math.Pi/180))
+	m.Set(0, 0, scale)
+	m.Set(1, 1, scale)
+	m.Set(2, 2, -far/(far-near))
+	m.Set(3, 2, -1)
+	m.Set(2, 3, -far*near/(far-near))
+}
+
+// Multiply the given point by our vector. Remember this is row-major order
+func (m *Mat44f) MultiplyPoint3(p Vec3f) Vec3f {
+	var out Vec3f
+	// We hope very much that Go will optimize the function calls for us,
+	// along with computing the constants.
+	out.X = p.X*m.Get(0, 0) + p.Y*m.Get(0, 1) + p.Z*m.Get(0, 2) + m.Get(0, 3)
+	out.Y = p.X*m.Get(1, 0) + p.Y*m.Get(1, 1) + p.Z*m.Get(1, 2) + m.Get(1, 3)
+	out.Z = p.X*m.Get(2, 0) + p.Y*m.Get(2, 1) + p.Z*m.Get(2, 2) + m.Get(2, 3)
+	w := p.X*m.Get(3, 0) + p.Y*m.Get(3, 1) + p.Z*m.Get(3, 2) + m.Get(3, 3)
+	if w != 1 {
+		out.X /= w
+		out.Y /= w
+		out.Z /= w
+	}
+	return out
+}
+
+type Facef [3]Vec3f
+
+type ObjModel struct {
+	Vertices []Vec3f
+	Faces    []Facef
+}
+
+// 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
+}

tinyrender1_perspective/render.go

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+package main
+
+import (
+	"math"
+)
+
+func Bresenham2(fb *Framebuffer, color uint, x0 int, y0 int, x1 int, y1 int) {
+	dx := int(math.Abs(float64(x1 - x0)))
+	sx := -1
+	if x0 < x1 {
+		sx = 1
+	}
+	dy := -int(math.Abs(float64(y1 - y0)))
+	sy := -1
+	if y0 < y1 {
+		sy = 1
+	}
+	err := dx + dy
+
+	for {
+		fb.SetSafe(uint(x0), uint(y0), color)
+		if x0 == x1 && y0 == y1 {
+			break
+		}
+		e2 := 2 * err
+		if e2 >= dy {
+			if x0 == x1 {
+				break
+			}
+			err += dy
+			x0 += sx
+		}
+		if e2 <= dx {
+			if y0 == y1 {
+				break
+			}
+			err += dx
+			y0 += sy
+		}
+	}
+}

tinyrender1_perspective/run.sh

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+#!/bin/sh
+
+if [ $# -ne 1 ]; then
+  echo "You must pass the basename for the .prof and .ppm"
+  exit 1
+fi
+
+echo "Building"
+go build
+echo "Running"
+./tinyrender1 "-cpuprofile=$1.prof" >"$1.ppm"