add Lambertian material

in_one_weekend/src/vec3.zig

@@ -24,7 +24,15 @@ pub const Vec3 = packed struct {
         };
     }
 
-    pub fn mul(self: Vec3, scalar: f32) Vec3 {
+    pub fn mul(self: Vec3, v: Vec3) Vec3 {
+        return Vec3{
+            .x = self.x * v.x,
+            .y = self.y * v.y,
+            .z = self.z * v.z,
+        };
+    }
+
+    pub fn mul_s(self: Vec3, scalar: f32) Vec3 {
         return Vec3{
             .x = self.x * scalar,
             .y = self.y * scalar,
@@ -60,14 +68,17 @@ pub const Vec3 = packed struct {
         };
     }
 
-    // pub fn unit_vector() Vec3 {
-    //     return
-    // }
-};
+    pub fn unit(self: Vec3) Vec3 {
+        return self.div(self.length());
+    }
 
-pub fn unitVector(vec: Vec3) Vec3 {
-    return vec.div(vec.length());
-}
+    pub fn nearZero(self: Vec3) bool {
+        const t = 1e-8;
+        return math.absFloat(self.x) < t
+            and math.absFloat(self.y) < t
+            and math.absFloat(self.z) < t;
+    }
+};
 
 pub fn random(rng: *Random, min: f32, max: f32) Vec3 {
     const range = max - min;
@@ -88,7 +99,7 @@ pub fn random_in_unit_sphere(rng: *Random) Vec3 {
 }
 
 pub fn random_unit_vector(rng: *Random) Vec3 {
-    return unitVector(random_in_unit_sphere(rng));
+    return random_in_unit_sphere(rng).unit();
 }
 
 pub fn random_in_hemisphere(rng: *Random, normal: Vec3) Vec3 {
@@ -97,7 +108,7 @@ pub fn random_in_hemisphere(rng: *Random, normal: Vec3) Vec3 {
         // In the same hemisphere as the normal
         return in_unit_sphere;
     } else {
-        return in_unit_sphere.mul(-1);
+        return in_unit_sphere.mul_s(-1);
     }
 }