add defocus blur

in_one_weekend/src/camera.zig

@@ -1,5 +1,6 @@
 const std = @import("std");
 const math = std.math;
+const Random = std.rand.Random;
 
 const Point3 = @import("vec3.zig").Point3;
 const Vec3 = @import("vec3.zig").Vec3;
@@ -9,11 +10,23 @@ fn degreesToRadians(degrees: f32) f32 {
     return degrees * math.pi / 180.0;
 }
 
+fn random_in_unit_disk(rng: *Random) Vec3 {
+    while (true) {
+        const p = Vec3{ .x = rng.float(f32) * 2 - 1, .y = rng.float(f32) * 2 - 1, .z = 0 };
+        if (p.length_squared() >= 1) continue;
+        return p;
+    }
+}
+
 pub const Camera = struct {
     origin: Point3,
     lowerLeftCorner: Point3,
     horizontal: Vec3,
     vertical: Vec3,
+    u: Vec3,
+    v: Vec3,
+    w: Vec3,
+    lensRadius: f32,
 
     pub fn init(
         lookFrom: Point3,
@@ -21,6 +34,8 @@ pub const Camera = struct {
         vup: Vec3,
         vfov: f32,
         aspectRatio: f32,
+        aperture: f32,
+        focusDist: f32,
     ) Camera {
         const theta = degreesToRadians(vfov);
         const h = math.tan(theta / 2);
@@ -33,22 +48,29 @@ pub const Camera = struct {
         const v = w.cross(u);
 
         const origin = lookFrom;
-        const horizontal = u.mul_s(viewportWidth);
-        const vertical = v.mul_s(viewportHeight);
-        const lowerLeftCorner = origin.sub(horizontal.div(2)).sub(vertical.div(2)).sub(w);
+        const horizontal = u.mul_s(viewportWidth).mul_s(focusDist);
+        const vertical = v.mul_s(viewportHeight).mul_s(focusDist);
+        const lowerLeftCorner = origin.sub(horizontal.div(2)).sub(vertical.div(2)).sub(w.mul_s(focusDist));
 
         return Camera {
             .origin = origin,
             .horizontal = horizontal,
             .vertical = vertical,
             .lowerLeftCorner = lowerLeftCorner,
+            .u = u,
+            .v = v,
+            .w = w,
+            .lensRadius = aperture / 2,
         };
     }
 
-    pub fn getRay(self: Camera, s: f32, t: f32) Ray {
+    pub fn getRay(self: Camera, s: f32, t: f32, rng: *Random) Ray {
+        const rd = random_in_unit_disk(rng).mul_s(self.lensRadius);
+        const offset = self.u.mul_s(rd.x).add(self.v.mul_s(rd.y));
+
         return Ray{
-            .origin = self.origin,
-            .direction = self.lowerLeftCorner.add(self.horizontal.mul_s(s)).add(self.vertical.mul_s(t)).sub(self.origin),
+            .origin = self.origin.add(offset),
+            .direction = self.lowerLeftCorner.add(self.horizontal.mul_s(s)).add(self.vertical.mul_s(t)).sub(self.origin).sub(offset),
         };
     }
 };

in_one_weekend/src/main.zig

@@ -123,12 +123,19 @@ pub fn main() anyerror!void {
     const world = World{ .spheres = spheres[0..spheres.len] };
 
     // Camera
+    const lookFrom = Point3{ .x = 3, .y = 3, .z = 2 };
+    const lookAt = Point3{ .x = 0, .y = 0, .z = -1 };
+    const vup = Vec3{ .x = 0, .y = 1, .z = 0 };
+    const distToFocus = lookFrom.sub(lookAt).length();
+    const aperture = 2.0;
     const camera = Camera.init(
-        Point3{ .x = -2, .y = 2, .z = 1 },
-        Point3{ .x = 0, .y = 0, .z = -1 },
-        Vec3{ .x = 0, .y = 1, .z = 0 },
+        lookFrom,
+        lookAt,
+        vup,
         20.0,
-        aspectRatio
+        aspectRatio,
+        aperture,
+        distToFocus
     );
 
     const window = sdl.c.SDL_CreateWindow(
@@ -186,7 +193,7 @@ 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 r = camera.getRay(u, v, &prng.random);
                     const sample = rayColor(r, world, &prng.random, maxDepth);
                     pixelColor.* = pixelColor.*.add(sample);