From e6ef8088e25750bca6ab61bda24fcb7e9e929ed1 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Mon, 24 Jun 2024 23:46:18 +0100
Subject: Chapter 13

---
 camera.go   | 26 +++++++++++++++++++++-----
 interval.go |  4 ----
 rtiaw.go    |  3 ++-
 vec3.go     | 15 ++++++++++++++-
 4 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/camera.go b/camera.go
index 66981aa..8ca0664 100644
--- a/camera.go
+++ b/camera.go
@@ -15,12 +15,16 @@ type Camera struct {
   Pixel00 Vec3
   AntiAliasing uint
   MaxDepth uint
+  DOF float64
+  DefDiskU Vec3
+  DefDiskV Vec3
 }
 
 func NewCamera(wi uint, ar float64,
                aa uint, md uint,
                vfov float64, lookfrom Vec3,
-               lookat Vec3, vup Vec3) (cam Camera) {
+               lookat Vec3, vup Vec3,
+               dof float64, fd float64) (cam Camera) {
   cam.ImageWidth = wi;
   cam.ImageHeight = uint(float64(cam.ImageWidth) / ar);
   if cam.ImageHeight < 1 {
@@ -30,11 +34,11 @@ func NewCamera(wi uint, ar float64,
   cam.AntiAliasing = aa;
   cam.MaxDepth = md;
   cam.Centre = lookfrom;
+  cam.DOF = dof;
 
-  focal_length := lookfrom.Sub(lookat).Mag();
   theta := vfov * maths.Pi / 180;
   h := maths.Tan(theta / 2)
-  viewport_height := 2.0 * h * focal_length;
+  viewport_height := 2.0 * h * fd;
   viewport_width := viewport_height *
                        float64(cam.ImageWidth) /
                        float64(cam.ImageHeight);
@@ -50,12 +54,16 @@ func NewCamera(wi uint, ar float64,
   cam.PDV = viewport_v.Div(SplatVec3(float64(cam.ImageHeight)));
 
   viewport_upperleft := cam.Centre.
-                        Sub(SplatVec3(focal_length).Mul(w)).
+                        Sub(SplatVec3(fd).Mul(w)).
                         Sub(viewport_u.Div(SplatVec3(2))).
                         Sub(viewport_v.Div(SplatVec3(2)));
   cam.Pixel00 = viewport_upperleft.
                  Add(cam.PDU.Add(cam.PDV).Div(SplatVec3(2)));
 
+  def_radius := fd * maths.Tan((cam.DOF / 2) * (maths.Pi / 180));
+  cam.DefDiskU = SplatVec3(def_radius).Mul(u);
+  cam.DefDiskV = SplatVec3(def_radius).Mul(v);
+
   return;
 }
 
@@ -84,7 +92,15 @@ func (cam Camera) GetRay(row uint, col uint) Ray {
   pixel_sample := cam.Pixel00.
                   Add(cam.PDU.Mul(SplatVec3(float64(col) + offset.X))).
                   Add(cam.PDV.Mul(SplatVec3(float64(row) + offset.Y)));
-  return Ray{cam.Centre, pixel_sample.Sub(cam.Centre), true};
+  origin := cam.Centre;
+  if cam.DOF > 0 {
+    p := RandomVec3OnUnitDisk();
+    origin = cam.Centre.
+              Add(SplatVec3(p.X).Mul(cam.DefDiskU)).
+              Add(SplatVec3(p.Y).Mul(cam.DefDiskV));
+  }
+  direction := pixel_sample.Sub(origin);
+  return Ray{origin, direction, true};
 }
 
 func unit_square() Vec3 {
diff --git a/interval.go b/interval.go
index b7deb68..763939a 100644
--- a/interval.go
+++ b/interval.go
@@ -34,7 +34,3 @@ func (i Interval) Clamp(x float64) float64 {
 func (i Interval) Sample() float64 {
   return rand.Float64() * i.Size() + i.Min;
 }
-
-func (i Interval) RandomVec3() Vec3 {
-  return Vec3{i.Sample(), i.Sample(), i.Sample()};
-}
diff --git a/rtiaw.go b/rtiaw.go
index 25dd971..ab2c503 100644
--- a/rtiaw.go
+++ b/rtiaw.go
@@ -25,7 +25,8 @@ func main() {
   cam := NewCamera(400, 16.0/9.0,
                    100, 50,
                    20, Vec3{-2, 2, 1},
-                   Vec3{0, 0, -1}, Vec3{0, 1, 0});
+                   Vec3{0, 0, -1}, Vec3{0, 1, 0},
+                   10.0, 3.4);
   cam.Render(world);
 
   dur := time.Since(start);
diff --git a/vec3.go b/vec3.go
index f590625..068ef6c 100644
--- a/vec3.go
+++ b/vec3.go
@@ -82,7 +82,7 @@ func RandomVec3OnUnitSphere() (v Vec3) {
   i := Interval{-1, 1}
 
   for true {
-    v = i.RandomVec3()
+    v = Vec3{i.Sample(), i.Sample(), i.Sample()}; 
     if v.MagSqr() < 1 {
       v = v.Unit();
       return;
@@ -92,6 +92,19 @@ func RandomVec3OnUnitSphere() (v Vec3) {
   return;
 }
 
+func RandomVec3OnUnitDisk() (v Vec3) {
+  i := Interval{-1, 1}
+
+  for true {
+    v = Vec3{i.Sample(), i.Sample(), 0}; 
+    if v.MagSqr() < 1 {
+      return;
+    }
+  }
+
+  return;
+}
+
 func (v Vec3) Reflect(n Vec3) Vec3 {
   return v.Sub(SplatVec3(2 * v.Dot(n)).Mul(n));
 }
-- 
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