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+/**********************************************************************
+* path tracing demo
+*
+* Copyright (c) 2019-2021 Dario Deledda. All rights reserved.
+* Use of this source code is governed by an MIT license
+* that can be found in the LICENSE file.
+*
+* This file contains a path tracer example in less of 500 line of codes
+* 3 demo scenes included
+*
+* This code is inspired by:
+* - "Realistic Ray Tracing" by Peter Shirley 2000 ISBN-13: 978-1568814612
+* - https://www.kevinbeason.com/smallpt/
+*
+* Known limitations:
+* - there are some approximation errors in the calculations
+* - to speed-up the code a cos/sin table is used
+* - the full precision code is present but commented, can be restored very easily
+* - an higher number of samples ( > 60) can block the program on higher resolutions
+* without a stack size increase
+* - as a recursive program this code depend on the stack size,
+* for higher number of samples increase the stack size
+* in linux: ulimit -s byte_size_of_the_stack
+* example: ulimit -s 16000000
+* - No OpenMP support
+**********************************************************************/
+import os
+import math
+import rand
+import time
+import term
+
+const (
+ inf = 1e+10
+ eps = 1e-4
+ f_0 = 0.0
+)
+
+//**************************** 3D Vector utility struct *********************
+struct Vec {
+mut:
+ x f64 = 0.0
+ y f64 = 0.0
+ z f64 = 0.0
+}
+
+[inline]
+fn (v Vec) + (b Vec) Vec {
+ return Vec{v.x + b.x, v.y + b.y, v.z + b.z}
+}
+
+[inline]
+fn (v Vec) - (b Vec) Vec {
+ return Vec{v.x - b.x, v.y - b.y, v.z - b.z}
+}
+
+[inline]
+fn (v Vec) * (b Vec) Vec {
+ return Vec{v.x * b.x, v.y * b.y, v.z * b.z}
+}
+
+[inline]
+fn (v Vec) dot(b Vec) f64 {
+ return v.x * b.x + v.y * b.y + v.z * b.z
+}
+
+[inline]
+fn (v Vec) mult_s(b f64) Vec {
+ return Vec{v.x * b, v.y * b, v.z * b}
+}
+
+[inline]
+fn (v Vec) cross(b Vec) Vec {
+ return Vec{v.y * b.z - v.z * b.y, v.z * b.x - v.x * b.z, v.x * b.y - v.y * b.x}
+}
+
+[inline]
+fn (v Vec) norm() Vec {
+ tmp_norm := 1.0 / math.sqrt(v.x * v.x + v.y * v.y + v.z * v.z)
+ return Vec{v.x * tmp_norm, v.y * tmp_norm, v.z * tmp_norm}
+}
+
+//********************************Image**************************************
+struct Image {
+ width int
+ height int
+ data &Vec
+}
+
+fn new_image(w int, h int) Image {
+ vecsize := int(sizeof(Vec))
+ return Image{
+ width: w
+ height: h
+ data: unsafe { &Vec(vcalloc(vecsize * w * h)) }
+ }
+}
+
+// write out a .ppm file
+fn (image Image) save_as_ppm(file_name string) {
+ npixels := image.width * image.height
+ mut f_out := os.create(file_name) or { panic(err) }
+ f_out.writeln('P3') or { panic(err) }
+ f_out.writeln('$image.width $image.height') or { panic(err) }
+ f_out.writeln('255') or { panic(err) }
+ for i in 0 .. npixels {
+ c_r := to_int(unsafe { image.data[i] }.x)
+ c_g := to_int(unsafe { image.data[i] }.y)
+ c_b := to_int(unsafe { image.data[i] }.z)
+ f_out.write_string('$c_r $c_g $c_b ') or { panic(err) }
+ }
+ f_out.close()
+}
+
+//********************************** Ray ************************************
+struct Ray {
+ o Vec
+ d Vec
+}
+
+// material types, used in radiance()
+enum Refl_t {
+ diff
+ spec
+ refr
+}
+
+//******************************** Sphere ***********************************
+struct Sphere {
+ rad f64 = 0.0 // radius
+ p Vec // position
+ e Vec // emission
+ c Vec // color
+ refl Refl_t // reflection type => [diffuse, specular, refractive]
+}
+
+fn (sp Sphere) intersect(r Ray) f64 {
+ op := sp.p - r.o // Solve t^2*d.d + 2*t*(o-p).d + (o-p).(o-p)-R^2 = 0
+ b := op.dot(r.d)
+ mut det := b * b - op.dot(op) + sp.rad * sp.rad
+
+ if det < 0 {
+ return 0
+ }
+
+ det = math.sqrt(det)
+
+ mut t := b - det
+ if t > eps {
+ return t
+ }
+
+ t = b + det
+ if t > eps {
+ return t
+ }
+ return 0
+}
+
+/*********************************** Scenes **********************************
+* 0) Cornell Box with 2 spheres
+* 1) Sunset
+* 2) Psychedelic
+* The sphere fileds are: Sphere{radius, position, emission, color, material}
+******************************************************************************/
+const (
+ cen = Vec{50, 40.8, -860} // used by scene 1
+ spheres = [
+ [/* scene 0 cornnel box */ Sphere{
+ rad: 1e+5
+ p: Vec{1e+5 + 1, 40.8, 81.6}
+ e: Vec{}
+ c: Vec{.75, .25, .25}
+ refl: .diff
+ }, /* Left */ Sphere{
+ rad: 1e+5
+ p: Vec{-1e+5 + 99, 40.8, 81.6}
+ e: Vec{}
+ c: Vec{.25, .25, .75}
+ refl: .diff
+ }, /* Rght */ Sphere{
+ rad: 1e+5
+ p: Vec{50, 40.8, 1e+5}
+ e: Vec{}
+ c: Vec{.75, .75, .75}
+ refl: .diff
+ }, /* Back */ Sphere{
+ rad: 1e+5
+ p: Vec{50, 40.8, -1e+5 + 170}
+ e: Vec{}
+ c: Vec{}
+ refl: .diff
+ }, /* Frnt */ Sphere{
+ rad: 1e+5
+ p: Vec{50, 1e+5, 81.6}
+ e: Vec{}
+ c: Vec{.75, .75, .75}
+ refl: .diff
+ }, /* Botm */ Sphere{
+ rad: 1e+5
+ p: Vec{50, -1e+5 + 81.6, 81.6}
+ e: Vec{}
+ c: Vec{.75, .75, .75}
+ refl: .diff
+ }, /* Top */ Sphere{
+ rad: 16.5
+ p: Vec{27, 16.5, 47}
+ e: Vec{}
+ c: Vec{1, 1, 1}.mult_s(.999)
+ refl: .spec
+ }, /* Mirr */ Sphere{
+ rad: 16.5
+ p: Vec{73, 16.5, 78}
+ e: Vec{}
+ c: Vec{1, 1, 1}.mult_s(.999)
+ refl: .refr
+ }, /* Glas */ Sphere{
+ rad: 600
+ p: Vec{50, 681.6 - .27, 81.6}
+ e: Vec{12, 12, 12}
+ c: Vec{}
+ refl: .diff
+ } /* Lite */],
+ [/* scene 1 sunset */ Sphere{
+ rad: 1600
+ p: Vec{1.0, 0.0, 2.0}.mult_s(3000)
+ e: Vec{1.0, .9, .8}.mult_s(1.2e+1 * 1.56 * 2)
+ c: Vec{}
+ refl: .diff
+ }, /* sun */ Sphere{
+ rad: 1560
+ p: Vec{1, 0, 2}.mult_s(3500)
+ e: Vec{1.0, .5, .05}.mult_s(4.8e+1 * 1.56 * 2)
+ c: Vec{}
+ refl: .diff
+ }, /* horizon sun2 */ Sphere{
+ rad: 10000
+ p: cen + Vec{0, 0, -200}
+ e: Vec{0.00063842, 0.02001478, 0.28923243}.mult_s(6e-2 * 8)
+ c: Vec{.7, .7, 1}.mult_s(.25)
+ refl: .diff
+ }, /* sky */ Sphere{
+ rad: 100000
+ p: Vec{50, -100000, 0}
+ e: Vec{}
+ c: Vec{.3, .3, .3}
+ refl: .diff
+ }, /* grnd */ Sphere{
+ rad: 110000
+ p: Vec{50, -110048.5, 0}
+ e: Vec{.9, .5, .05}.mult_s(4)
+ c: Vec{}
+ refl: .diff
+ }, /* horizon brightener */ Sphere{
+ rad: 4e+4
+ p: Vec{50, -4e+4 - 30, -3000}
+ e: Vec{}
+ c: Vec{.2, .2, .2}
+ refl: .diff
+ }, /* mountains */ Sphere{
+ rad: 26.5
+ p: Vec{22, 26.5, 42}
+ e: Vec{}
+ c: Vec{1, 1, 1}.mult_s(.596)
+ refl: .spec
+ }, /* white Mirr */ Sphere{
+ rad: 13
+ p: Vec{75, 13, 82}
+ e: Vec{}
+ c: Vec{.96, .96, .96}.mult_s(.96)
+ refl: .refr
+ }, /* Glas */ Sphere{
+ rad: 22
+ p: Vec{87, 22, 24}
+ e: Vec{}
+ c: Vec{.6, .6, .6}.mult_s(.696)
+ refl: .refr
+ } /* Glas2 */],
+ [/* scene 3 Psychedelic */ Sphere{
+ rad: 150
+ p: Vec{50 + 75, 28, 62}
+ e: Vec{1, 1, 1}.mult_s(0e-3)
+ c: Vec{1, .9, .8}.mult_s(.93)
+ refl: .refr
+ }, Sphere{
+ rad: 28
+ p: Vec{50 + 5, -28, 62}
+ e: Vec{1, 1, 1}.mult_s(1e+1)
+ c: Vec{1, 1, 1}.mult_s(0)
+ refl: .diff
+ }, Sphere{
+ rad: 300
+ p: Vec{50, 28, 62}
+ e: Vec{1, 1, 1}.mult_s(0e-3)
+ c: Vec{1, 1, 1}.mult_s(.93)
+ refl: .spec
+ }],
+ ] // end of scene array
+)
+
+//********************************** Utilities ******************************
+[inline]
+fn clamp(x f64) f64 {
+ if x < 0 {
+ return 0
+ }
+ if x > 1 {
+ return 1
+ }
+ return x
+}
+
+[inline]
+fn to_int(x f64) int {
+ p := math.pow(clamp(x), 1.0 / 2.2)
+ return int(p * 255.0 + 0.5)
+}
+
+fn intersect(r Ray, spheres &Sphere, nspheres int) (bool, f64, int) {
+ mut d := 0.0
+ mut t := inf
+ mut id := 0
+ for i := nspheres - 1; i >= 0; i-- {
+ d = unsafe { spheres[i] }.intersect(r)
+ if d > 0 && d < t {
+ t = d
+ id = i
+ }
+ }
+ return (t < inf), t, id
+}
+
+// some casual random function, try to avoid the 0
+fn rand_f64() f64 {
+ x := rand.u32() & 0x3FFF_FFFF
+ return f64(x) / f64(0x3FFF_FFFF)
+}
+
+const (
+ cache_len = 65536 // the 2*pi angle will be splitted in 65536 part
+ cache_mask = cache_len - 1 // mask to speed-up the module process
+)
+
+struct Cache {
+mut:
+ sin_tab [65536]f64
+ cos_tab [65536]f64
+}
+
+fn new_tabs() Cache {
+ mut c := Cache{}
+ inv_len := 1.0 / f64(cache_len)
+ for i in 0 .. cache_len {
+ x := f64(i) * math.pi * 2.0 * inv_len
+ c.sin_tab[i] = math.sin(x)
+ c.cos_tab[i] = math.cos(x)
+ }
+ return c
+}
+
+//************ Cache for sin/cos speed-up table and scene selector **********
+const (
+ tabs = new_tabs()
+)
+
+//****************** main function for the radiance calculation *************
+fn radiance(r Ray, depthi int, scene_id int) Vec {
+ if depthi > 1024 {
+ eprintln('depthi: $depthi')
+ eprintln('')
+ return Vec{}
+ }
+ mut depth := depthi // actual depth in the reflection tree
+ mut t := 0.0 // distance to intersection
+ mut id := 0 // id of intersected object
+ mut res := false // result of intersect
+
+ v_1 := 1.0
+ // v_2 := f64(2.0)
+
+ scene := spheres[scene_id]
+ // res, t, id = intersect(r, id, tb.scene)
+ res, t, id = intersect(r, scene.data, scene.len)
+ if !res {
+ return Vec{}
+ }
+ // if miss, return black
+
+ obj := scene[id] // the hit object
+
+ x := r.o + r.d.mult_s(t)
+ n := (x - obj.p).norm()
+
+ nl := if n.dot(r.d) < 0.0 { n } else { n.mult_s(-1) }
+
+ mut f := obj.c
+
+ // max reflection
+ mut p := f.z
+ if f.x > f.y && f.x > f.z {
+ p = f.x
+ } else {
+ if f.y > f.z {
+ p = f.y
+ }
+ }
+
+ depth++
+ if depth > 5 {
+ if rand_f64() < p {
+ f = f.mult_s(f64(1.0) / p)
+ } else {
+ return obj.e // R.R.
+ }
+ }
+
+ if obj.refl == .diff { // Ideal DIFFUSE reflection
+ // **Full Precision**
+ // r1 := f64(2.0 * math.pi) * rand_f64()
+
+ // tabbed speed-up
+ r1 := rand.u32() & cache_mask
+
+ r2 := rand_f64()
+ r2s := math.sqrt(r2)
+
+ w := nl
+
+ mut u := if math.abs(w.x) > f64(0.1) { Vec{0, 1, 0} } else { Vec{1, 0, 0} }
+ u = u.cross(w).norm()
+
+ v := w.cross(u)
+
+ // **Full Precision**
+ // d := (u.mult_s(math.cos(r1) * r2s) + v.mult_s(math.sin(r1) * r2s) + w.mult_s(1.0 - r2)).norm()
+
+ // tabbed speed-up
+ d := (u.mult_s(tabs.cos_tab[r1] * r2s) + v.mult_s(tabs.sin_tab[r1] * r2s) +
+ w.mult_s(math.sqrt(f64(1.0) - r2))).norm()
+
+ return obj.e + f * radiance(Ray{x, d}, depth, scene_id)
+ } else {
+ if obj.refl == .spec { // Ideal SPECULAR reflection
+ return obj.e + f * radiance(Ray{x, r.d - n.mult_s(2.0 * n.dot(r.d))}, depth, scene_id)
+ }
+ }
+
+ refl_ray := Ray{x, r.d - n.mult_s(2.0 * n.dot(r.d))} // Ideal dielectric REFRACTION
+ into := n.dot(nl) > 0 // Ray from outside going in?
+
+ nc := f64(1.0)
+ nt := f64(1.5)
+
+ nnt := if into { nc / nt } else { nt / nc }
+
+ ddn := r.d.dot(nl)
+ cos2t := v_1 - nnt * nnt * (v_1 - ddn * ddn)
+ if cos2t < 0.0 { // Total internal reflection
+ return obj.e + f * radiance(refl_ray, depth, scene_id)
+ }
+
+ dirc := if into { f64(1) } else { f64(-1) }
+ tdir := (r.d.mult_s(nnt) - n.mult_s(dirc * (ddn * nnt + math.sqrt(cos2t)))).norm()
+
+ a := nt - nc
+ b := nt + nc
+ r0 := a * a / (b * b)
+ c := if into { v_1 + ddn } else { v_1 - tdir.dot(n) }
+
+ re := r0 + (v_1 - r0) * c * c * c * c * c
+ tr := v_1 - re
+ pp := f64(.25) + f64(.5) * re
+ rp := re / pp
+ tp := tr / (v_1 - pp)
+
+ mut tmp := Vec{}
+ if depth > 2 {
+ // Russian roulette
+ tmp = if rand_f64() < pp {
+ radiance(refl_ray, depth, scene_id).mult_s(rp)
+ } else {
+ radiance(Ray{x, tdir}, depth, scene_id).mult_s(tp)
+ }
+ } else {
+ tmp = (radiance(refl_ray, depth, scene_id).mult_s(re)) +
+ (radiance(Ray{x, tdir}, depth, scene_id).mult_s(tr))
+ }
+ return obj.e + (f * tmp)
+}
+
+//*********************** beam scan routine *********************************
+fn ray_trace(w int, h int, samps int, file_name string, scene_id int) Image {
+ image := new_image(w, h)
+
+ // inverse costants
+ w1 := f64(1.0 / f64(w))
+ h1 := f64(1.0 / f64(h))
+ samps1 := f64(1.0 / f64(samps))
+
+ cam := Ray{Vec{50, 52, 295.6}, Vec{0, -0.042612, -1}.norm()} // cam position, direction
+ cx := Vec{f64(w) * 0.5135 / f64(h), 0, 0}
+ cy := cx.cross(cam.d).norm().mult_s(0.5135)
+ mut r := Vec{}
+
+ // speed-up constants
+ v_1 := f64(1.0)
+ v_2 := f64(2.0)
+
+ // OpenMP injection point! #pragma omp parallel for schedule(dynamic, 1) shared(c)
+ for y := 0; y < h; y++ {
+ term.cursor_up(1)
+ eprintln('Rendering (${samps * 4} spp) ${(100.0 * f64(y)) / (f64(h) - 1.0):5.2f}%')
+ for x in 0 .. w {
+ i := (h - y - 1) * w + x
+ mut ivec := unsafe { &image.data[i] }
+ // we use sx and sy to perform a square subsampling of 4 samples
+ for sy := 0; sy < 2; sy++ {
+ for sx := 0; sx < 2; sx++ {
+ r = Vec{0, 0, 0}
+ for _ in 0 .. samps {
+ r1 := v_2 * rand_f64()
+ dx := if r1 < v_1 { math.sqrt(r1) - v_1 } else { v_1 - math.sqrt(v_2 - r1) }
+
+ r2 := v_2 * rand_f64()
+ dy := if r2 < v_1 { math.sqrt(r2) - v_1 } else { v_1 - math.sqrt(v_2 - r2) }
+
+ d := cx.mult_s(((f64(sx) + 0.5 + dx) * 0.5 + f64(x)) * w1 - .5) +
+ cy.mult_s(((f64(sy) + 0.5 + dy) * 0.5 + f64(y)) * h1 - .5) + cam.d
+ r = r + radiance(Ray{cam.o +
+ d.mult_s(140.0), d.norm()}, 0, scene_id).mult_s(samps1)
+ }
+ tmp_vec := Vec{clamp(r.x), clamp(r.y), clamp(r.z)}.mult_s(.25)
+ (*ivec) = *ivec + tmp_vec
+ }
+ }
+ }
+ }
+ return image
+}
+
+fn main() {
+ if os.args.len > 6 {
+ eprintln('Usage:\n path_tracing [samples] [image.ppm] [scene_n] [width] [height]')
+ exit(1)
+ }
+ mut width := 320 // width of the rendering in pixels
+ mut height := 200 // height of the rendering in pixels
+ mut samples := 4 // number of samples per pixel, increase for better quality
+ mut scene_id := 0 // scene to render [0 cornell box,1 sunset,2 psyco]
+ mut file_name := 'image.ppm' // name of the output file in .ppm format
+
+ if os.args.len >= 2 {
+ samples = os.args[1].int() / 4
+ }
+ if os.args.len >= 3 {
+ file_name = os.args[2]
+ }
+ if os.args.len >= 4 {
+ scene_id = os.args[3].int()
+ }
+ if os.args.len >= 5 {
+ width = os.args[4].int()
+ }
+ if os.args.len == 6 {
+ height = os.args[5].int()
+ }
+ // change the seed for a different result
+ rand.seed([u32(2020), 0])
+
+ t1 := time.ticks()
+
+ eprintln('Path tracing samples: $samples, file_name: $file_name, scene_id: $scene_id, width: $width, height: $height')
+ eprintln('')
+ image := ray_trace(width, height, samples, file_name, scene_id)
+ t2 := time.ticks()
+
+ eprintln('Rendering finished. Took: ${(t2 - t1):5}ms')
+
+ image.save_as_ppm(file_name)
+ t3 := time.ticks()
+
+ eprintln('Image saved as [$file_name]. Took: ${(t3 - t2):5}ms')
+}