From 9c69e2f4e2a15acbaaabf1a9213185f9f7da171a Mon Sep 17 00:00:00 2001
From: Altagos <jakob@altagos.dev>
Date: Fri, 12 Apr 2024 22:44:23 +0200
Subject: [PATCH] schlick approximation

---
 src/main.zig     |  4 +++-
 src/material.zig | 10 +++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/src/main.zig b/src/main.zig
index 9cfbb6c..0cdb675 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -29,13 +29,15 @@ pub fn main() !void {
     // Setting up the world
     var material_ground = Material.lambertian(zm.f32x4(0.8, 0.8, 0.0, 1.0));
     var material_center = Material.lambertian(zm.f32x4(0.1, 0.2, 0.5, 1.0));
-    var material_left = Material.dielectric(1.0 / 1.33);
+    var material_left = Material.dielectric(1.5);
+    var material_bubble = Material.dielectric(1.0 / 1.5);
     var material_right = Material.metal(zm.f32x4(0.8, 0.6, 0.2, 1.0), 1.0);
 
     var world = HittableList.init(allocator);
     try world.add(Hittable.sphere(Sphere{ .center = zm.f32x4(0, -100.5, -1, 0), .radius = 100, .mat = &material_ground }));
     try world.add(Hittable.sphere(Sphere{ .center = zm.f32x4(0, 0, -1, 0), .radius = 0.5, .mat = &material_center }));
     try world.add(Hittable.sphere(Sphere{ .center = zm.f32x4(-1, 0, -1, 0), .radius = 0.5, .mat = &material_left }));
+    try world.add(Hittable.sphere(Sphere{ .center = zm.f32x4(-1, 0, -1, 0), .radius = 0.4, .mat = &material_bubble }));
     try world.add(Hittable.sphere(Sphere{ .center = zm.f32x4(1, 0, -1, 0), .radius = 0.5, .mat = &material_right }));
 
     const s = spall.trace(@src(), "Raytracer", .{});
diff --git a/src/material.zig b/src/material.zig
index 3f3fec1..f5fa743 100644
--- a/src/material.zig
+++ b/src/material.zig
@@ -1,3 +1,5 @@
+const math = @import("std").math;
+
 const zm = @import("zmath");
 
 const hittable = @import("hittable.zig");
@@ -69,7 +71,7 @@ pub const Dielectric = struct {
 
         const cannot_refract = ri * sin_theta > 1.0;
         const direction = blk: {
-            if (cannot_refract) {
+            if (cannot_refract or reflectance(cos_theta, ri) > util.randomF32()) {
                 break :blk util.reflect(unit_direction, rec.normal);
             } else {
                 break :blk util.refract(unit_direction, rec.normal, ri);
@@ -78,4 +80,10 @@ pub const Dielectric = struct {
 
         return Ray.init(rec.p, direction);
     }
+
+    fn reflectance(cosine: f32, refraction_index: f32) f32 {
+        var r0 = (1 - refraction_index) / (1 + refraction_index);
+        r0 = r0 * r0;
+        return r0 + (1 - r0) * math.pow(f32, 1 - cosine, 5);
+    }
 };
-- 
2.51.2