From 62317d57ae4f73a1c9634196d49a53df2832386b Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Sun, 14 Aug 2022 11:36:50 -0700
Subject: [PATCH] zigrtiow: implement depth of field.

---
 zigrtiow/src/camera.zig | 23 +++++++++++++++++++----
 zigrtiow/src/main.zig   |  8 +++++++-
 zigrtiow/src/vec.zig    |  7 +++++++
 3 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/zigrtiow/src/camera.zig b/zigrtiow/src/camera.zig
index 8232728..4504f78 100644
--- a/zigrtiow/src/camera.zig
+++ b/zigrtiow/src/camera.zig
@@ -5,6 +5,7 @@ const Ray = @import("./ray.zig").Ray;
 
 const Point3 = vec.Point3;
 const Vec3 = vec.Vec3;
+const random_in_unit_disk = vec.random_in_unit_disk;
 const math = std.math;
 const pi = math.pi;
 const tan = math.tan;
@@ -20,6 +21,10 @@ pub const Camera = struct {
     lower_left_corner: Point3,
     horizontal: Vec3,
     vertical: Vec3,
+    u: Vec3,
+    v: Vec3,
+    w: Vec3,
+    lens_radius: f32,
 
     pub fn init(
         lookfrom: Point3,
@@ -27,6 +32,8 @@ pub const Camera = struct {
         vup: Vec3,
         vfov: f32, // vertical field-of-view in degrees
         aspect_ratio: f32,
+        aperature: f32,
+        focus_dist: f32,
     ) Camera {
         const theta = degrees_to_radians(vfov);
         const h = tan(theta / 2);
@@ -38,18 +45,26 @@ pub const Camera = struct {
         const v = w.cross(u);
 
         const origin = lookfrom;
-        const horizontal = u.scale(viewport_width);
-        const vertical = v.scale(viewport_height);
-        const lower_left_corner = origin.sub(horizontal.scale(0.5)).sub(vertical.scale(0.5)).sub(w);
+        const horizontal = u.scale(focus_dist * viewport_width);
+        const vertical = v.scale(focus_dist * viewport_height);
+        const lower_left_corner = origin.sub(horizontal.scale(0.5)).sub(vertical.scale(0.5)).sub(w.scale(focus_dist));
+
+        const lens_radius = aperature / 2;
 
         return Camera{
             .origin = origin,
             .horizontal = horizontal,
             .vertical = vertical,
             .lower_left_corner = lower_left_corner,
+            .u = u,
+            .v = v,
+            .w = w,
+            .lens_radius = lens_radius,
         };
     }
     pub fn get_ray(camera: Camera, s: f32, t: f32) Ray {
-        return Ray.init(camera.origin, camera.lower_left_corner.add(camera.horizontal.scale(s).add(camera.vertical.scale(t).sub(camera.origin))));
+        const rd = random_in_unit_disk().scale(camera.lens_radius);
+        const offset = camera.u.scale(rd.x()).add(camera.v.scale(rd.y()));
+        return Ray.init(camera.origin.add(offset), camera.lower_left_corner.add(camera.horizontal.scale(s).add(camera.vertical.scale(t).sub(camera.origin).sub(offset))));
     }
 };
diff --git a/zigrtiow/src/main.zig b/zigrtiow/src/main.zig
index 6705770..a0802da 100644
--- a/zigrtiow/src/main.zig
+++ b/zigrtiow/src/main.zig
@@ -108,7 +108,13 @@ pub fn main() anyerror!void {
     const world = Hittable{ .hittable_list = tmp_world };
 
     // Camera
-    const cam = Camera.init(Point3.init(-2, 2, 1), Point3.init(0, 0, -1), Vec3.init(0, 1, 0), 20, aspect_ratio);
+    const lookfrom = Point3.init(3, 3, 2);
+    const lookat = Point3.init(0, 0, -1);
+    const vup = Vec3.init(0, 1, 0);
+    const dist_to_focus = lookfrom.sub(lookat).length();
+    const aperature = 2;
+
+    const cam = Camera.init(lookfrom, lookat, vup, 20, aspect_ratio, aperature, dist_to_focus);
 
     // Render
     const Node = Queue(Task).Node;
diff --git a/zigrtiow/src/vec.zig b/zigrtiow/src/vec.zig
index ba13406..c1c098d 100644
--- a/zigrtiow/src/vec.zig
+++ b/zigrtiow/src/vec.zig
@@ -66,6 +66,13 @@ pub const Vec3 = struct {
     }
 };
 
+pub fn random_in_unit_disk() Vec3 {
+    while (true) {
+        const p = Vec3.init(rand.float(f32) * 2 - 1, rand.float(f32) * 2 - 1, 0);
+        if (p.length_squared() >= 1) continue;
+        return p;
+    }
+}
 pub fn random_in_unit_sphere() Vec3 {
     while (true) {
         const p = Vec3.random();