bounce rays around

in_one_weekend/src/color.zig

@@ -9,9 +9,13 @@ pub fn averageColor(pixelColor: *Color, samplesPerPixel: i32) Color {
     // const scale = 1.0 / @intToFloat(f32, samplesPerPixel);
     var scaledColor = pixelColor.*.div(@intToFloat(f32, samplesPerPixel));
 
+    const r = math.sqrt(scaledColor.x);
+    const g = math.sqrt(scaledColor.y);
+    const b = math.sqrt(scaledColor.z);
+
     return Color{
-        .x = math.clamp(scaledColor.x, 0, 0.999),
-        .y = math.clamp(scaledColor.y, 0, 0.999),
-        .z = math.clamp(scaledColor.z, 0, 0.999),
+        .x = math.clamp(r, 0, 0.999),
+        .y = math.clamp(g, 0, 0.999),
+        .z = math.clamp(b, 0, 0.999),
     };
 }

in_one_weekend/src/main.zig

@@ -1,5 +1,6 @@
 const std = @import("std");
 const print = std.debug.print;
+const Random = std.rand.Random;
 const sdl = @import("sdl.zig");
 const vec3 = @import("vec3.zig");
 const Vec3 = vec3.Vec3;
@@ -33,9 +34,16 @@ fn hitSphere(center: Point3, radius: f32, ray: Ray) f32 {
     }
 }
 
-fn rayColor(ray: Ray, world: World) Color {
-    if (world.hit(ray, 0, 99999)) |hit| {
-        return hit.normal.add(Vec3{ .x = 1, .y = 1, .z = 1}).div(2);
+fn rayColor(ray: Ray, world: World, rng: *Random, depth: i32) Color {
+    // If we've exceeded the ray bounce limit, no more light is gathered.
+    if (depth <= 0) {
+        return Color{ .x = 0, .y = 0, .z = 0 };
+    }
+
+    if (world.hit(ray, 0.001, 99999)) |hit| {
+        const target = hit.p.add(hit.normal).add(vec3.random_in_unit_sphere(rng));
+        const newRay = Ray{ .origin = hit.p, .direction = target.sub(hit.p)};
+        return rayColor(newRay, world, rng, depth - 1).div(2);
     }
     const unitDirection = vec3.unitVector(ray.direction);
     const t = 0.5 * (unitDirection.y + 1.0);
@@ -76,6 +84,7 @@ pub fn main() anyerror!void {
     const imageWidth = 600;
     const imageHeight = @floatToInt(usize, imageWidth / aspectRatio);
     const samplesPerPixel = 100;
+    const maxDepth = 5;
 
     // World
     const spheres = [_]Sphere{
@@ -143,7 +152,7 @@ pub fn main() anyerror!void {
                     const u = (@intToFloat(f32, i) + prng.random.float(f32)) / @intToFloat(f32, (imageWidth - 1));
                     const v = (@intToFloat(f32, j) + prng.random.float(f32)) / @intToFloat(f32, (imageHeight - 1));
                     const r = camera.getRay(u, v);
-                    const sample = rayColor(r, world);
+                    const sample = rayColor(r, world, &prng.random, maxDepth);
                     pixelColor.* = pixelColor.*.add(sample);
 
                     const averageColor = color.averageColor(pixelColor, @intCast(i32, k));

in_one_weekend/src/vec3.zig

@@ -1,4 +1,7 @@
-const math = @import("std").math;
+const std = @import("std");
+const print = std.debug.print;
+const math = std.math;
+const Random = std.rand.Random;
 
 pub const Vec3 = packed struct {
     x: f32 = 0.0,
@@ -66,6 +69,24 @@ pub fn unitVector(vec: Vec3) Vec3 {
     return vec.div(vec.length());
 }
 
+pub fn random(rng: *Random, min: f32, max: f32) Vec3 {
+    const range = max - min;
+    return Vec3{
+        .x = rng.*.float(f32) * range + min,
+        .y = rng.*.float(f32) * range + min,
+        .z = rng.*.float(f32) * range + min,
+    };
+}
+
+pub fn random_in_unit_sphere(rng: *Random) Vec3 {
+    while (true) {
+        const v = random(rng, -1, 1);        
+        if (v.length_squared() < 1) {
+            return v;
+        }
+    }
+}
+
 pub const Point3 = Vec3;
 
 const assert = @import("std").debug.assert;