zigrtiow: use hemisphere random rays.

zigrtiow/src/color.zig

@@ -8,11 +8,11 @@ pub fn write_color(c: Color, samples_per_pixel: isize) anyerror!void {
     var g = c.y();
     var b = c.z();
 
-    // Divide the color by the number of samples.
-    var scale = 1.0 / @intToFloat(f32, samples_per_pixel);
-    r *= scale;
-    g *= scale;
-    b *= scale;
+    // Divide the color by the number of samples and gamma-correct for gamma=2.0.
+    const scale = 1.0 / @intToFloat(f32, samples_per_pixel);
+    r = @sqrt(scale * r);
+    g = @sqrt(scale * g);
+    b = @sqrt(scale * b);
 
     // Write the translated [0,255] value of each color component.
     var ir = @floatToInt(u8, 256 * clamp(r, 0, 0.999));

zigrtiow/src/main.zig

@@ -15,7 +15,7 @@ const Point3 = vec.Point3;
 const Ray = ray.Ray;
 const Sphere = sphere.Sphere;
 const Vec3 = vec.Vec3;
-const random_in_unit_sphere = vec.random_in_unit_sphere;
+const random_in_hemisphere = vec.random_in_hemisphere;
 const info = std.log.info;
 const write_color = color.write_color;
 
@@ -23,10 +23,10 @@ fn ray_color(r: Ray, world: Hittable, depth: isize) Color {
     // If we've exceeded the ray bounce limit, no more light is gathered.
     if (depth <= 0) return Color.init(0, 0, 0);
 
-    var hit = world.hit(r, 0, std.math.inf(f32));
+    var hit = world.hit(r, 0.0001, std.math.inf(f32));
     if (hit) |rec| {
-        const target = rec.p.add(rec.normal.add(random_in_unit_sphere()));
-        return ray_color(Ray.init(rec.p, target.sub(rec.p)), world, depth - 1);
+        const target = rec.p.add(rec.normal.add(random_in_hemisphere(rec.normal)));
+        return ray_color(Ray.init(rec.p, target.sub(rec.p)), world, depth - 1).scale(0.5);
     }
     var unit_direction = r.direction().unit();
     const t = 0.5 * (unit_direction.y() + 1);

zigrtiow/src/vec.zig

@@ -47,9 +47,9 @@ pub const Vec3 = struct {
     /// Return value in unit cube from -1, 1
     pub fn random() Vec3 {
         return Vec3.init(
-            rand.float(f32) * 2 - 0.5,
-            rand.float(f32) * 2 - 0.5,
-            rand.float(f32) * 2 - 0.5,
+            rand.float(f32) * 2 - 1,
+            rand.float(f32) * 2 - 1,
+            rand.float(f32) * 2 - 1,
         );
     }
 };
@@ -61,6 +61,17 @@ pub fn random_in_unit_sphere() Vec3 {
         return p;
     }
 }
+pub fn random_unit_vector() Vec3 {
+    return random_in_unit_sphere().unit();
+}
+pub fn random_in_hemisphere(normal: Vec3) Vec3 {
+    const in_unit_sphere = random_in_unit_sphere();
+    if (in_unit_sphere.dot(normal) > 0.0) { // In the same hemisphere as the normal
+        return in_unit_sphere;
+    } else {
+        return in_unit_sphere.scale(-1);
+    }
+}
 
 pub const Color = Vec3;
 pub const Point3 = Vec3;