diff --git a/.github/workflows/periodic.yml b/.github/workflows/periodic.yml
index c13e4d31c4..7d4c6fd3cf 100644
--- a/.github/workflows/periodic.yml
+++ b/.github/workflows/periodic.yml
@@ -49,6 +49,8 @@ jobs:
       run:  ./v -o v2 cmd/v && ./v2 -o v3 cmd/v
     - name: Test symlink
       run:  sudo ./v symlink
+    - name: Ensure thirdparty/cJSON/cJSON.o is compiled, before running tests.
+      run:  ./v examples/json.v
     - name: Set up pg database
       run: |
         brew services start postgresql
diff --git a/.gitignore b/.gitignore
index 30b1928d31..434cbfb9f7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -57,3 +57,4 @@ info.log
 # vim/emacs editor backup files
 *~
 thirdparty/freetype/
+cachegrind.out.*
diff --git a/examples/.gitignore b/examples/.gitignore
index 6f0b11537e..287844245b 100644
--- a/examples/.gitignore
+++ b/examples/.gitignore
@@ -13,6 +13,8 @@
 /hello_v_js
 /fibonacci
 /sqlite
+/path_tracing
+*.ppm
 empty_gg_freetype
 game_of_life/life_gg
 random_ips
diff --git a/examples/path_tracing.v b/examples/path_tracing.v
index 11fa518cb7..5e753efa78 100644
--- a/examples/path_tracing.v
+++ b/examples/path_tracing.v
@@ -1,5 +1,4 @@
 /**********************************************************************
-*
 * path tracing demo
 *
 * Copyright (c) 2019-2020 Dario Deledda. All rights reserved.
@@ -24,17 +23,19 @@
 *   in linux: ulimit -s byte_size_of_the_stack
 *   example: ulimit -s 16000000
 * - No OpenMP support 
-*
 **********************************************************************/
 import os
 import math
 import rand
+import time
 
-/******************************************************************************
-*
-* 3D Vector utility struct
-*
-******************************************************************************/
+const (
+	inf = f64(1e+10)
+	eps = f64(1e-4)
+	f_0 = f64(0.0)
+)
+	
+/***************************** 3D Vector utility struct **********************/
 struct Vec {     
 mut:  
    x f64 = f64(0.0)
@@ -82,11 +83,38 @@ fn (v Vec) norm () Vec {
 	return Vec{ v.x * tmp_norm , v.y * tmp_norm, v.z * tmp_norm }
 }
 
-/******************************************************************************
-*
-* Ray
-*
-******************************************************************************/
+/*********************************Image***************************************/
+struct Image {
+	width int
+	height int
+	data &Vec
+}
+
+fn new_image(w int, h int) Image {
+	return Image{
+		width: w,
+		height: h,
+		data: &Vec(calloc(sizeof(Vec)*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 { exit }
+	f_out.writeln('P3')
+	f_out.writeln('${image.width} ${image.height}')
+	f_out.writeln('255')
+	for i in 0..npixels {
+		c_r := to_int(image.data[i].x)
+		c_g := to_int(image.data[i].y)
+		c_b := to_int(image.data[i].z)
+		f_out.write('$c_r $c_g $c_b ')
+	}
+	f_out.close()
+}
+
+/*********************************** Ray *************************************/
 struct Ray {
 	o Vec
 	d Vec
@@ -99,11 +127,7 @@ enum Refl_t {
 	refr 
 }  
 
-/******************************************************************************
-*
-* Sphere
-*
-******************************************************************************/
+/********************************* Sphere ************************************/
 struct Sphere {
 	rad f64 = f64(0.0)   // radius
 	p Vec                // position
@@ -112,59 +136,52 @@ struct Sphere {
 	refl Refl_t          // reflection type => [diffuse, specular, refractive]
 }
 
-[inline]
 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 
-	mut t     := f64(0.0)
-	eps       := f64(1e-4)
 	b         := op.dot(r.d)
 	mut det   := b * b - op.dot(op) + sp.rad * sp.rad
 
 	if det < 0 {
 		return f64(0)
-	} else {
-		det = math.sqrt(det)
 	}
-
-	t = b - det
-	if t > eps { return t }
+	
+	det = math.sqrt(det)
+	
+	mut t := b - det
+	if t > eps {
+		return t
+	}
+	
 	t = b + det
-	if t > eps { return t }
+	if t > eps {
+		return t
+	}
 	return f64(0)
 }
 
-/******************************************************************************
-*
-* Scenes
-*
+/*********************************** Scenes **********************************
 * 0) Cornell Box with 2 spheres
 * 1) Sunset
 * 2) Psychedelic
-*
-* the sphere fileds are: Sphere{radius, position, emission, color, material}
-*
+* The sphere fileds are: Sphere{radius, position, emission, color, material}
 ******************************************************************************/
-const (
-
+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{1e-16, 1e-16, 1e-16}, refl: .diff},//Frnt 
+	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{27.0,16.5,47.0}     , e: Vec{}        , c: Vec{1,1,1}.mult_s(.999) , refl: .spec},//Mirr 
+	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{1e-16, 1e-16, 1e-16}, refl: .diff} //Lite 
-]
+	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
+[// 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
 
@@ -175,10 +192,10 @@ spheres = [
 	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
+[// 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}
@@ -188,15 +205,11 @@ spheres = [
 
 )
 
-/******************************************************************************
-*
-* Utility
-*
-******************************************************************************/
+/*********************************** Utilities *******************************/
 [inline]
 fn clamp(x f64) f64 {
-	if x < f64(0.0) { return f64(0.0) }
-	if x > f64(1.0) { return f64(1.0) }
+	if x < 0 { return 0 }
+	if x > 1 { return 1 }
 	return x
 }
 
@@ -206,39 +219,27 @@ fn to_int(x f64) int {
 	return int(p*f64(255.0)+f64(0.5))
 }
 
-[inline]
-//fn intersect(r Ray, id1 int, scene int) (bool, f64, int){
-fn intersect(r Ray, id1 int, spheres []Sphere) (bool, f64, int){
+fn intersect(r Ray, spheres &Sphere, nspheres int) (bool, f64, int){
 	mut d  := f64(0)
-	inf    := f64(1e+20)
-	mut t  := f64(1e+20)
-	//mut i  := spheres[scene].len-1
-	mut i  := spheres.len-1
-	mut id := id1
-	for i >= 0 {
-		//d = spheres[scene][i].intersect(r)
+	mut t  := inf
+	mut id := 0
+	for i:=nspheres-1; i >= 0; i-- {
 		d = spheres[i].intersect(r)
-		if d != 0.0 && d < t {
+		if d > 0 && d < t {
 			t = d
 			id = i
 		}
-		i--
 	}
 	return (t < inf) , t, id
 }
 
 // some casual random function, try to avoid the 0
-[inline]
 fn rand_f64() f64 {
- 	x := (C.rand()+1) & 0x3FFF_FFFF
- 	return f64(x)/f64(0x3FFF_FFFF)
+	x := (C.rand()+1) & 0x3FFF_FFFF
+	return f64(x)/f64(0x3FFF_FFFF)
 }
 
-/******************************************************************************
-*
-* Cache for sin/cos speed-up table and scene selector
-*
-******************************************************************************/
+
 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
@@ -246,243 +247,236 @@ const(
 
 struct Cache {
 mut:
-	scene int = 0
 	sin_tab [cache_len]f64
 	cos_tab [cache_len]f64
 }
 
-fn (c mut Cache) fill() {
-	inv_len := 1.0 / f64(cache_len)
+fn new_tabs() Cache {
+	mut c := Cache{}
+	inv_len := f64(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, tb &Cache) Vec {
-		mut depth   := depthi      // actual depth in the reflection tree
-		mut t       := f64(0)      // distance to intersection 
-		mut id      := 0           // id of intersected object
-		mut res     := false       // result of intersect
-
-		v_1 := f64(1.0)
-		//v_2 := f64(2.0)
-
-		//res, t, id = intersect(r, id, tb.scene)
-		res, t, id = intersect(r, id, spheres[tb.scene])
-		if !res { return Vec{} }  //if miss, return black 
-
-		obj := spheres[tb.scene][id]        // the hit object 
-
-		x := r.o + r.d.mult_s(t)
-		n := (x - obj.p).norm()
-		
-		mut nl := n
-		if n.dot(r.d) >= 0.0 {
-			nl = 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(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 := C.rand() & cache_mask
-			
-			r2  := rand_f64()
-			r2s := math.sqrt(r2)
-
-			w   := nl
-
-			mut u := Vec{1, 0, 0}
-			if math.abs(w.x) > 0.1 {
-				u = Vec{0, 1, 0}
-			} 
-			u = u.cross(w)
-			u = u.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(tb.cos_tab[r1] * r2s) + v.mult_s(tb.sin_tab[r1] * r2s) + w.mult_s(1.0 - r2)).norm()
-			
-			return obj.e + (f * radiance(Ray{x, d}, depth, tb))
-		} 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, tb))
-			}
-		}
-
-		refl_ray := Ray{x, r.d - n.mult_s(2.0 * n.dot(r.d))}     // Ideal dielectric REFRACTION
-		into     := n.dot(nl) > 0.0                          // Ray from outside going in? 
-		
-		nc       := f64(1.0)
-		nt       := f64(1.5)
-
-		mut nnt      := nt / nc
-		if into { nnt = nc / nt }
-
-		ddn      := r.d.dot(nl)
-		mut cos2t:= f64(0)
-		cos2t = v_1 - nnt * nnt * (v_1 - ddn * ddn)
-
-		if cos2t < 0.0  {   // Total internal reflection
-			return obj.e + (f * radiance(refl_ray, depth, tb))
-		}
-
-		mut dirc := -1
-		if into { dirc = 1 }
-		tdir := r.d.mult_s(nnt) -n.mult_s(dirc).mult_s(ddn * nnt + math.sqrt(cos2t)).norm()
-
-		a  := nt - nc
-		b  := nt + nc
-		r0 := a * a / (b * b) 
-		mut c  := v_1 - tdir.dot(n)
-		if into { c = v_1 + ddn }
-
-		re := r0 + (v_1 - r0) * c * c * c * c * c
-		tr := v_1 - re
-		p  = f64(.25) + f64(.5) * re
-		rp := re / p
-		tp := tr / (v_1 - p)
-
-	mut res_f := obj.e
-
-	mut tmp := radiance(Ray{x, tdir}, depth, tb).mult_s(tp)
-	if rand_f64() < p {
-		tmp = radiance(refl_ray, depth, tb).mult_s(rp)
+/******************* main function for the radiance calculation **************/
+fn radiance(r Ray, depthi int, scene_id int) Vec {
+	sin_tab := &f64( tabs.sin_tab )
+	cos_tab := &f64( tabs.cos_tab )
+	mut depth   := depthi      // actual depth in the reflection tree
+	mut t       := f64(0)      // distance to intersection 
+	mut id      := 0           // id of intersected object
+	mut res     := false       // result of intersect
+	
+	v_1 := f64(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 := C.rand() & 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(cos_tab[r1] * r2s) + v.mult_s(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 {
-		res_f = res_f + f * tmp
-		return res_f
+		// 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)
+}
 
-	tmp1 := radiance(refl_ray, depth, tb).mult_s(re) + radiance( Ray{x, tdir}, depth, tb).mult_s(tr)
-	res_f = res_f + f * tmp1
-	return res_f
-} 
-
-/******************************************************************************
-*
-* beam scan routine
-*
-******************************************************************************/
-fn ray_trace(w int, h int, samps int, file_name string, tb &Cache) {
-
+/************************ 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 / w)
 	h1     := f64(1.0 / h)
 	samps1 := f64(1.0 / samps)
-
-	cam   := Ray{Vec{50, 52, 296.5},  Vec{0, -0.042612, -1}.norm()} // cam position, direction
-	cx    := Vec{ f64(w) * .5135 / f64(h), 0, 0}
-	cy    := ((cx.cross(cam.d)).norm()).mult_s(0.5135)
-	mut c := [Vec{}].repeat(w * h)
+	
+	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++ {
-		eprint("\rRendering (${samps * 4} spp) ${(100.0 * f64(y)) / (f64(h) - 1.0)}%")
+		eprint("\rRendering (${samps * 4} spp) ${(100.0 * f64(y)) / (f64(h) - 1.0):5.2f}%")
 		for x := 0; x < w; x++ {
-
+			
 			i := (h - y - 1) * w + x
+			mut ivec := &image.data[i]
 			// we use sx and sy to perform a square subsampling of 4 samples
-			for sy := f64(0.5) ; sy < 2.5; sy += 1.0 {
-				for sx := f64(0.5); sx < 2.5; sx += 1.0 {
-					r.x = 0
-					r.y = 0
-					r.z = 0
+			for sy := 0; sy < 2; sy ++ {
+				for sx := 0; sx < 2; sx ++ {
+					r = Vec{0,0,0}
 					for s := 0; s < samps; s++ {
-						// speed-up constants
-						v_1 := f64(1.0)
-						v_2 := f64(2.0)
-
 						r1 := v_2 * rand_f64()
-						mut dx := v_1 - math.sqrt(v_2 - r1)
-						if r1 < v_1 { dx = math.sqrt(r1) - v_1 }
-
+						dx := if r1 < v_1 { math.sqrt(r1) - v_1 } else { v_1 - math.sqrt(v_2 - r1) }
+						
 						r2 := v_2 * rand_f64()
-						mut dy := v_1 - math.sqrt(v_2 - r2)
-						if r2 < v_1 { dy = math.sqrt(r2) - v_1 }
-
-                        d := cx.mult_s( ( (sx + dx)*0.5 + f64(x))*w1 - .5) + 
-                             cy.mult_s( ( (sy + dy)*0.5 + f64(y))*h1 - .5) + cam.d
-
-                        r = r + radiance(Ray{cam.o+d.mult_s(140.0), d.norm()}, 0, tb).mult_s(samps1)
-
+						dy := if r2 < v_1 { math.sqrt(r2) - v_1 } else { v_1 - math.sqrt(v_2 - r2) }
+						
+                        d := cx.mult_s( ( (f64(sx) + 0.5 + dx)*0.5 + f64(x))*w1 - .5) + 
+							cy.mult_s( ( (f64(sy) + 0.5 + dy)*0.5 + f64(y))*h1 - .5) + cam.d
+                        r = r + radiance(Ray{cam.o+d.mult_s(140.0), d.norm()}, 0, scene_id).mult_s(samps1)
 					}
 					tmp_vec := Vec{clamp(r.x),clamp(r.y),clamp(r.z)}.mult_s(.25)
-					c[i] = c[i] + tmp_vec
+					*ivec = *ivec + tmp_vec
 				}
 			}
 		} 
 	}
-	eprintln('\nRendering finished.')
-
-	//
-	// write out a .ppm file
-	//
-	mut f_out := os.create(file_name) or { exit }
-	f_out.writeln('P3')
-	f_out.writeln('${w} ${h}')
-	f_out.writeln('255')
-	for i in 0..w*h {
-		c_r := to_int(c[i].x)
-		c_g := to_int(c[i].y)
-		c_b := to_int(c[i].z)
-		f_out.write('$c_r $c_g $c_b ')
-	}
-	f_out.close()
-
-	println("image saved as [${file_name}]")
+	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()
+	}
+	
 	// init the rand, using the same seed allows to obtain the same result in different runs
 	// change the seed from 2020 for different results
-	rand.seed(2020)  
+	rand.seed(2020)	 
 	
-	// init the sin/cos cache table 
-	mut tb := Cache{}
-	tb.fill()
+	t1:=time.ticks()
 
-	width    := 1280  // width of the rendering in pixels
-	height   := 1280  // height of the rendering in pixels
-	samples  := 10    // number of samples*4 per pixel, increase for better quality
-	tb.scene = 1      // scene to render [0 cornell box,1 sunset,2 psyco]  
-	file_name := "image.ppm" // name of the output file in .ppm format
-
-	ray_trace(width, height, samples, file_name, tb)
+	image := ray_trace(width, height, samples, file_name, scene_id)	
+	t2:=time.ticks()
+	
+	eprintln('\nRendering finished. Took: ${t2-t1:5d}ms')
+	
+	image.save_as_ppm( file_name )	
+	t3:=time.ticks()
+	
+	eprintln('Image saved as [${file_name}]. Took: ${t3-t2:5d}ms')
 }
diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 5779cd1a08..170524e32e 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -116,8 +116,10 @@ pub fn (a mut array) sort_with_compare(compare voidptr) {
 // a.insert(0, &i)
 // ----------------------------
 pub fn (a mut array) insert(i int, val voidptr) {
-	if i < 0 || i > a.len {
-		panic('array.insert: index out of range (i == $i, a.len == $a.len)')
+	$if !no_bounds_checking? {
+		if i < 0 || i > a.len {
+			panic('array.insert: index out of range (i == $i, a.len == $a.len)')
+		}
 	}
 	a.ensure_cap(a.len + 1)
 	size := a.element_size
@@ -135,8 +137,10 @@ pub fn (a mut array) prepend(val voidptr) {
 
 // array.delete deletes array element at the given index
 pub fn (a mut array) delete(i int) {
-	if i < 0 || i >= a.len {
-		panic('array.delete: index out of range (i == $i, a.len == $a.len)')
+	$if !no_bounds_checking? {
+		if i < 0 || i >= a.len {
+			panic('array.delete: index out of range (i == $i, a.len == $a.len)')
+		}
 	}
 	size := a.element_size
 	C.memmove(a.data + i * size, a.data + (i + 1) * size, (a.len - i) * size)
@@ -150,24 +154,30 @@ pub fn (a mut array) clear() {
 
 // Private function. Used to implement array[] operator
 fn (a array) get(i int) voidptr {
-	if i < 0 || i >= a.len {
-		panic('array.get: index out of range (i == $i, a.len == $a.len)')
+	$if !no_bounds_checking? {
+		if i < 0 || i >= a.len {
+			panic('array.get: index out of range (i == $i, a.len == $a.len)')
+		}
 	}
 	return a.data + i * a.element_size
 }
 
 // array.first returns the first element of the array
 pub fn (a array) first() voidptr {
-	if a.len == 0 {
-		panic('array.first: array is empty')
+	$if !no_bounds_checking? {
+		if a.len == 0 {
+			panic('array.first: array is empty')
+		}
 	}
 	return a.data + 0
 }
 
 // array.last returns the last element of the array
 pub fn (a array) last() voidptr {
-	if a.len == 0 {
-		panic('array.last: array is empty')
+	$if !no_bounds_checking? {
+		if a.len == 0 {
+			panic('array.last: array is empty')
+		}
 	}
 	return a.data + (a.len - 1) * a.element_size
 }
@@ -176,9 +186,11 @@ pub fn (a array) last() voidptr {
 // array.left returns a new array using the same buffer as the given array
 // with the first `n` elements of the given array.
 fn (a array) left(n int) array {
-	if n < 0 {
-		panic('array.left: index is negative (n == $n)')
-	}
+//	$if !no_bounds_checking? {
+//		if n < 0 {
+//			panic('array.left: index is negative (n == $n)')
+//		}
+//	}
 	if n >= a.len {
 		return a.slice(0, a.len)
 	}
@@ -190,9 +202,11 @@ fn (a array) left(n int) array {
 // If `n` is bigger or equal to the length of the given array,
 // returns an empty array of the same type as the given array.
 fn (a array) right(n int) array {
-	if n < 0 {
-		panic('array.right: index is negative (n == $n)')
-	}
+//	$if !no_bounds_checking? {
+//		if n < 0 {
+//			panic('array.right: index is negative (n == $n)')
+//		}
+//	}
 	if n >= a.len {
 		return new_array(0, 0, a.element_size)
 	}
@@ -206,14 +220,16 @@ fn (a array) right(n int) array {
 // set to the number of the elements in the slice.
 fn (a array) slice(start, _end int) array {
 	mut end := _end
-	if start > end {
-		panic('array.slice: invalid slice index ($start > $end)')
-	}
-	if end > a.len {
-		panic('array.slice: slice bounds out of range ($end >= $a.len)')
-	}
-	if start < 0 {
-		panic('array.slice: slice bounds out of range ($start < 0)')
+	$if !no_bounds_checking? {
+		if start > end {
+			panic('array.slice: invalid slice index ($start > $end)')
+		}
+		if end > a.len {
+			panic('array.slice: slice bounds out of range ($end >= $a.len)')
+		}
+		if start < 0 {
+			panic('array.slice: slice bounds out of range ($start < 0)')
+		}
 	}
 	l := end - start
 	res := array{
@@ -249,14 +265,16 @@ pub fn (a array) clone() array {
 
 fn (a array) slice_clone(start, _end int) array {
 	mut end := _end
-	if start > end {
-		panic('array.slice: invalid slice index ($start > $end)')
-	}
-	if end > a.len {
-		panic('array.slice: slice bounds out of range ($end >= $a.len)')
-	}
-	if start < 0 {
-		panic('array.slice: slice bounds out of range ($start < 0)')
+	$if !no_bounds_checking? {
+		if start > end {
+			panic('array.slice: invalid slice index ($start > $end)')
+		}
+		if end > a.len {
+			panic('array.slice: slice bounds out of range ($end >= $a.len)')
+		}
+		if start < 0 {
+			panic('array.slice: slice bounds out of range ($start < 0)')
+		}
 	}
 	l := end - start
 	res := array{
@@ -270,8 +288,10 @@ fn (a array) slice_clone(start, _end int) array {
 
 // Private function. Used to implement assigment to the array element.
 fn (a mut array) set(i int, val voidptr) {
-	if i < 0 || i >= a.len {
-		panic('array.set: index out of range (i == $i, a.len == $a.len)')
+	$if !no_bounds_checking? {
+		if i < 0 || i >= a.len {
+			panic('array.set: index out of range (i == $i, a.len == $a.len)')
+		}
 	}
 	C.memcpy(a.data + a.element_size * i, val, a.element_size)
 }
diff --git a/vlib/builtin/float.v b/vlib/builtin/float.v
index abd3438aa8..d0a9d3ddea 100644
--- a/vlib/builtin/float.v
+++ b/vlib/builtin/float.v
@@ -33,20 +33,25 @@ pub fn (x f64) strlong() string {
 	return tmpstr
 }
 
+[inline]
 fn f32_abs(a f32) f32 {
 	return if a < 0 { -a } else { a }
 }
 
+[inline]
 fn f64_abs(a f64) f64 {
 	return if a < 0 { -a } else { a }
 }
 
 // compare floats using C epsilon
 // ==
+
+[inline]
 pub fn (a f64) eq(b f64) bool {
 	return f64_abs(a - b) <= C.DBL_EPSILON
 }
 
+[inline]
 pub fn (a f32) eq(b f32) bool {
 	return f32_abs(a - b) <= C.FLT_EPSILON
 }
diff --git a/vlib/builtin/string.v b/vlib/builtin/string.v
index b9297f3f72..69bb5338dd 100644
--- a/vlib/builtin/string.v
+++ b/vlib/builtin/string.v
@@ -518,8 +518,10 @@ fn (s string) substr2(start, _end int, end_max bool) string {
 }
 
 pub fn (s string) substr(start, end int) string {
-	if start > end || start > s.len || end > s.len || start < 0 || end < 0 {
-		panic('substr($start, $end) out of bounds (len=$s.len)')
+	$if !no_bounds_checking? {
+		if start > end || start > s.len || end > s.len || start < 0 || end < 0 {
+			panic('substr($start, $end) out of bounds (len=$s.len)')
+		}
 	}
 	len := end - start
 	mut res := string{
@@ -1043,8 +1045,10 @@ pub fn (u ustring) count(substr ustring) int {
 }
 
 pub fn (u ustring) substr(_start, _end int) string {
-	if _start > _end || _start > u.len || _end > u.len || _start < 0 || _end < 0 {
-		panic('substr($_start, $_end) out of bounds (len=$u.len)')
+	$if !no_bounds_checking? {
+		if _start > _end || _start > u.len || _end > u.len || _start < 0 || _end < 0 {
+			panic('substr($_start, $_end) out of bounds (len=$u.len)')
+		}
 	}
 	end := if _end >= u.len { u.s.len } else { u.runes[_end] }
 	return u.s.substr(u.runes[_start], end)
@@ -1065,15 +1069,19 @@ pub fn (u ustring) right(pos int) string {
 }
 
 fn (s string) at(idx int) byte {
-	if idx < 0 || idx >= s.len {
-		panic('string index out of range: $idx / $s.len')
+	$if !no_bounds_checking? {
+		if idx < 0 || idx >= s.len {
+			panic('string index out of range: $idx / $s.len')
+		}
 	}
 	return s.str[idx]
 }
 
 pub fn (u ustring) at(idx int) string {
-	if idx < 0 || idx >= u.len {
-		panic('string index out of range: $idx / $u.runes.len')
+	$if !no_bounds_checking? {
+		if idx < 0 || idx >= u.len {
+			panic('string index out of range: $idx / $u.runes.len')
+		}
 	}
 	return u.substr(idx, idx + 1)
 }
diff --git a/vlib/compiler/cheaders.v b/vlib/compiler/cheaders.v
index c2e8a629b7..b3e52f816b 100644
--- a/vlib/compiler/cheaders.v
+++ b/vlib/compiler/cheaders.v
@@ -140,6 +140,25 @@ $c_common_macros
 #define DEFAULT_LE(a, b) (a <= b)
 #define DEFAULT_GT(a, b) (a > b)
 #define DEFAULT_GE(a, b) (a >= b)
+
+// NB: macro_fXX_eq and macro_fXX_ne are NOT used 
+// in the generated C code. They are here just for 
+// completeness/testing.
+
+#define macro_f64_eq(a, b) (a == b)
+#define macro_f64_ne(a, b) (a != b)
+#define macro_f64_lt(a, b) (a <  b)
+#define macro_f64_le(a, b) (a <= b)
+#define macro_f64_gt(a, b) (a >  b)
+#define macro_f64_ge(a, b) (a >= b)
+
+#define macro_f32_eq(a, b) (a == b)
+#define macro_f32_ne(a, b) (a != b)
+#define macro_f32_lt(a, b) (a <  b)
+#define macro_f32_le(a, b) (a <= b)
+#define macro_f32_gt(a, b) (a >  b)
+#define macro_f32_ge(a, b) (a >= b)
+
 //================================== GLOBALS =================================*/
 byte g_str_buf[1024];
 int load_so(byteptr);
diff --git a/vlib/compiler/expression.v b/vlib/compiler/expression.v
index 353a10be1e..eaf76fff16 100644
--- a/vlib/compiler/expression.v
+++ b/vlib/compiler/expression.v
@@ -217,6 +217,10 @@ fn (p mut Parser) bterm() string {
 		if is_float && p.cur_fn.name != 'f32_abs' && p.cur_fn.name != 'f64_abs' {
 			p.gen(')')
 			match tok {
+				// NB: For more precision/stability, the == and != float
+				// comparisons are done with V functions that use the epsilon
+				// constants for the given type.
+				// Everything else uses native comparisons (C macros) for speed.
 				.eq {
 					p.cgen.set_placeholder(ph, '${expr_type}_eq(')
 				}
@@ -224,16 +228,16 @@ fn (p mut Parser) bterm() string {
 					p.cgen.set_placeholder(ph, '${expr_type}_ne(')
 				}
 				.le {
-					p.cgen.set_placeholder(ph, '${expr_type}_le(')
+					p.cgen.set_placeholder(ph, 'macro_${expr_type}_le(')
 				}
 				.ge {
-					p.cgen.set_placeholder(ph, '${expr_type}_ge(')
+					p.cgen.set_placeholder(ph, 'macro_${expr_type}_ge(')
 				}
 				.gt {
-					p.cgen.set_placeholder(ph, '${expr_type}_gt(')
+					p.cgen.set_placeholder(ph, 'macro_${expr_type}_gt(')
 				}
 				.lt {
-					p.cgen.set_placeholder(ph, '${expr_type}_lt(')
+					p.cgen.set_placeholder(ph, 'macro_${expr_type}_lt(')
 				}
 				else {
 				}}