add Lambertian material

in_one_weekend/src/material.zig

@@ -0,0 +1,35 @@
+const std = @import("std");
+const Random = std.rand.Random;
+
+const vec3 = @import("vec3.zig");
+const Color = @import("color.zig").Color;
+const Ray = @import("ray.zig").Ray;
+const HitRecord = @import("hittable.zig").HitRecord;
+
+pub const MaterialType = enum {
+    Lambertian,
+};
+
+pub const Material = struct {
+    materialType: MaterialType,
+    color: Color,
+};
+
+pub const ScatteredRay = struct {
+    ray: Ray,
+    color: Color,
+};
+
+pub fn scatter(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 = hit.material.color,
+    };
+}