added hemispherical scattering, switched to ppm version 6

src/vec3.rs

@@ -1,4 +1,4 @@
-use std::{ops::{Add, Sub, AddAssign, SubAssign, Mul, Div, MulAssign, DivAssign}};
+use std::ops::{Add, Sub, AddAssign, SubAssign, Mul, Div, MulAssign, DivAssign, Neg};
 
 use crate::rtweekend::{random_f64, random_range_f64};
 
@@ -89,6 +89,20 @@ impl Sub for Vec3 {
     }
 }
 
+impl Neg for Vec3 {
+    type Output = Self;
+
+    fn neg(self) -> Self::Output {
+        Self {
+            elements: [
+                -self.x(),
+                -self.y(),
+                -self.z()
+            ]
+        }
+    }
+}
+
 impl Mul<f64> for Vec3 {
     type Output = Self;
 
@@ -185,4 +199,17 @@ pub fn random_in_unit_sphere() -> Vec3 {
         }
         return p;
     }
+}
+
+pub fn random_unit_vector() -> Vec3 {
+    random_in_unit_sphere().unit_vector()
+}
+
+pub fn random_in_hemisphere(normal: &Vec3) -> Vec3 {
+    let in_unit_sphere = random_in_unit_sphere();
+    if in_unit_sphere.dot(&normal) > 0.0 {
+        return in_unit_sphere;
+    } else {
+        return -in_unit_sphere;
+    }
 }