From c842fcf713e9c7e6777019a6822feb9ed1aefd07 Mon Sep 17 00:00:00 2001
From: Fabien Freling <public@ffreling.com>
Date: Thu, 27 May 2021 21:19:31 +0200
Subject: [PATCH] implement Material as tagged union

---
 in_one_weekend/src/main.zig     | 24 ++++++-----
 in_one_weekend/src/material.zig | 73 ++++++++++++++++++---------------
 2 files changed, 53 insertions(+), 44 deletions(-)

diff --git a/in_one_weekend/src/main.zig b/in_one_weekend/src/main.zig
index ab41cc1..656f66b 100644
--- a/in_one_weekend/src/main.zig
+++ b/in_one_weekend/src/main.zig
@@ -14,8 +14,6 @@ const World = @import("world.zig").World;
 const Camera = @import("camera.zig").Camera;
 const material = @import("material.zig");
 const Material = material.Material;
-const MaterialType = material.MaterialType;
-const scatter = @import("material.zig").scatter;
 
 // From: https://github.com/Nelarius/weekend-raytracer-zig/blob/master/src/main.zig
 // See https://github.com/zig-lang/zig/issues/565
@@ -46,7 +44,7 @@ fn rayColor(ray: Ray, world: World, rng: *Random, depth: i32) Color {
     }
 
     if (world.hit(ray, 0.001, 99999)) |hit| {
-        if (scatter(ray, hit, rng)) |sRay| {
+        if (material.scatter(ray, hit, rng)) |sRay| {
             return sRay.color.mul(rayColor(sRay.ray, world, rng, depth - 1));
         }
         return Color{ .x = 0, .y = 0, .z = 0 };
@@ -94,20 +92,24 @@ pub fn main() anyerror!void {
 
     // World
     const materialGround = Material{
-        .materialType = .Lambertian,
-        .color = Color{ .x = 0.8, .y = 0.8, .z = 0.0 },
+        .lambertian = material.Lambertian{
+            .color = Color{ .x = 0.8, .y = 0.8, .z = 0.0 }
+        }
     };
     const materialCenter = Material{
-        .materialType = .Lambertian,
-        .color = Color{ .x = 0.7, .y = 0.3, .z = 0.3 },
+        .lambertian = material.Lambertian{
+            .color = Color{ .x = 0.7, .y = 0.3, .z = 0.3 }
+        }
     };
     const materialLeft = Material{
-        .materialType = .Metal,
-        .color = Color{ .x = 0.8, .y = 0.8, .z = 0.8 },
+        .metal = material.Metal{
+            .color = Color{ .x = 0.8, .y = 0.8, .z = 0.8 }
+        }
     };
     const materialRight = Material{
-        .materialType = .Metal,
-        .color = Color{ .x = 0.8, .y = 0.6, .z = 0.2 },
+        .metal = material.Metal{
+            .color = Color{ .x = 0.8, .y = 0.6, .z = 0.2 }
+        }
     };
 
     const spheres = [_]Sphere{
diff --git a/in_one_weekend/src/material.zig b/in_one_weekend/src/material.zig
index 174bd05..95edca2 100644
--- a/in_one_weekend/src/material.zig
+++ b/in_one_weekend/src/material.zig
@@ -7,13 +7,41 @@ const Ray = @import("ray.zig").Ray;
 const HitRecord = @import("hittable.zig").HitRecord;
 
 pub const MaterialType = enum {
-    Lambertian,
-    Metal,
+    lambertian,
+    metal,
 };
 
-pub const Material = struct {
-    materialType: MaterialType,
+pub const Lambertian = struct {
     color: Color,
+
+    pub fn scatter(self: Lambertian, ray: Ray, hit: HitRecord, rng: *Random) ?ScatteredRay {
+        var scatterDirection = hit.normal.add(vec3.random_unit_vector(rng));
+        // Catch degenerate scatter direction
+        if (scatterDirection.nearZero()) {
+            scatterDirection = hit.normal;
+        }
+        return ScatteredRay{
+            .ray = Ray{ .origin = hit.p, .direction = scatterDirection},
+            .color = self.color,
+        };
+    }
+};
+
+pub const Metal = struct {
+    color: Color,
+    // fuzzy: f32,
+
+    pub fn scatter(self: Metal, ray: Ray, hit: HitRecord, rng: *Random) ?ScatteredRay {
+        const reflected = ray.direction.unit().reflect(hit.normal);
+        const scattered = Ray{ .origin = hit.p, .direction = reflected };
+        if (scattered.direction.dot(hit.normal) <= 0) {
+            return null;
+        }
+        return ScatteredRay{
+            .ray = scattered,
+            .color = self.color,
+        };
+    }
 };
 
 pub const ScatteredRay = struct {
@@ -21,35 +49,14 @@ pub const ScatteredRay = struct {
     color: Color,
 };
 
+pub const Material = union(MaterialType) {
+    lambertian: Lambertian,
+    metal: Metal,
+};
+
 pub fn scatter(ray: Ray, hit: HitRecord, rng: *Random) ?ScatteredRay {
-    const scatteredDirection = switch (hit.material.materialType) {
-
-        .Lambertian => blk: {
-            var scatterDirection = hit.normal.add(vec3.random_unit_vector(rng));
-            // Catch degenerate scatter direction
-            if (scatterDirection.nearZero()) {
-                scatterDirection = hit.normal;
-            }
-            break :blk scatterDirection;
-        },
-
-        .Metal => blk: {
-            const reflected = ray.direction.unit().reflect(hit.normal);
-            const scattered = Ray{ .origin = hit.p, .direction = reflected };
-            if (scattered.direction.dot(hit.normal) <= 0) {
-                break :blk null;
-            }
-            break :blk scattered.direction;
-        },
-
+    return switch (hit.material) {
+        .lambertian => |m| m.scatter(ray, hit, rng),
+        .metal => |m| m.scatter(ray, hit, rng),
     };
-
-    if (scatteredDirection) |dir| {
-        return ScatteredRay{
-            .ray = Ray{ .origin = hit.p, .direction = dir},
-            .color = hit.material.color,
-        };
-    }
-
-    return null;
 }
\ No newline at end of file