Faster and static random number generator

Cargo.lock

@@ -97,21 +97,21 @@ dependencies = [
 
 [[package]]
 name = "jpeg-decoder"
-version = "0.2.5"
+version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "be7ef4b99870f0c9f2fc2f20dbef72707e2bcca675bb9196734cf433e999b0c5"
+checksum = "9478aa10f73e7528198d75109c8be5cd7d15fb530238040148d5f9a22d4c5b3b"
 
 [[package]]
 name = "libc"
-version = "0.2.125"
+version = "0.2.126"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5916d2ae698f6de9bfb891ad7a8d65c09d232dc58cc4ac433c7da3b2fd84bc2b"
+checksum = "349d5a591cd28b49e1d1037471617a32ddcda5731b99419008085f72d5a53836"
 
 [[package]]
 name = "miniz_oxide"
-version = "0.5.1"
+version = "0.5.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d2b29bd4bc3f33391105ebee3589c19197c4271e3e5a9ec9bfe8127eeff8f082"
+checksum = "6f5c75688da582b8ffc1f1799e9db273f32133c49e048f614d22ec3256773ccc"
 dependencies = [
  "adler",
 ]

Cargo.toml

@@ -7,4 +7,4 @@ edition = "2021"
 
 [dependencies]
 image = { version = "0.24.2", default-features = false, features = ["jpeg", "png", "pnm"] }
-rand = "0.8.5"
+rand = { version = "0.8.5", features = ["small_rng"] }

src/color.rs

@@ -18,9 +18,9 @@ pub fn put_color(img: &mut RgbImage, pixel_color: &Color, x: u32, y: u32, sample
     let mut b = pixel_color.z();
 
     let scale = 1.0 / samples_per_pixel as f64;
-    r *= scale;
+    r = (scale*r).sqrt();
-    g *= scale;
+    g = (scale*g).sqrt();
-    b *= scale;
+    b = (scale*b).sqrt();
 
     img.put_pixel(
         x,

src/main.rs

@@ -26,7 +26,7 @@ fn ray_color(r: &Ray, world: &HittableList, depth: u32) -> Color {
         return Color::new(0.0,0.0,0.0);
     }
 
-    if world.hit(r, 0.0, f64::INFINITY, &mut rec) {
+    if world.hit(r, 0.001, f64::INFINITY, &mut rec) {
         let target = rec.p + rec.normal + Vec3::random_in_unit_sphere();
         return 0.5 * ray_color(&Ray::new(rec.p, target - rec.p), world, depth-1);
     }

src/utility.rs

@@ -1,8 +1,13 @@
-use rand::Rng;
+use rand::prelude::*;
+use std::cell::RefCell;
+
+thread_local! {
+    static RNG: RefCell<SmallRng> = RefCell::new(SmallRng::from_entropy())
+}
 
 /// generates random number 0<= x < 1
 pub fn random_f64() -> f64 {
-    rand::thread_rng().gen_range(0.0..1.0)
+    RNG.with(|rng| (*rng.borrow_mut()).gen())
 }
 
 pub fn random_rng(min: f64, max: f64) -> f64 {