From c64284af4f5fd44360b88261a1c49a36f8bc7344 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Mon, 24 Jun 2024 23:23:45 +0100
Subject: Chapter 12

---
 camera.go | 26 ++++++++++++++++++--------
 rtiaw.go  |  5 ++++-
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/camera.go b/camera.go
index f33d98a..66981aa 100644
--- a/camera.go
+++ b/camera.go
@@ -2,6 +2,7 @@ package main
 
 import (
   "fmt"
+  maths "math"
   "os"
 )
 
@@ -16,8 +17,11 @@ type Camera struct {
   MaxDepth uint
 }
 
-func NewCamera(w uint, ar float64, aa uint, md uint) (cam Camera) {
-  cam.ImageWidth = w;
+func NewCamera(wi uint, ar float64,
+               aa uint, md uint,
+               vfov float64, lookfrom Vec3,
+               lookat Vec3, vup Vec3) (cam Camera) {
+  cam.ImageWidth = wi;
   cam.ImageHeight = uint(float64(cam.ImageWidth) / ar);
   if cam.ImageHeight < 1 {
     cam.ImageHeight = 1;
@@ -25,22 +29,28 @@ func NewCamera(w uint, ar float64, aa uint, md uint) (cam Camera) {
 
   cam.AntiAliasing = aa;
   cam.MaxDepth = md;
+  cam.Centre = lookfrom;
 
-  focal_length := 1.0;
-  viewport_height := 2.0;
+  focal_length := lookfrom.Sub(lookat).Mag();
+  theta := vfov * maths.Pi / 180;
+  h := maths.Tan(theta / 2)
+  viewport_height := 2.0 * h * focal_length;
   viewport_width := viewport_height *
                        float64(cam.ImageWidth) /
                        float64(cam.ImageHeight);
-  cam.Centre = SplatVec3(0);
 
-  viewport_u := Vec3{viewport_width, 0, 0};
-  viewport_v := Vec3{0, -viewport_height, 0};
+  w := lookfrom.Sub(lookat).Unit();
+  u := vup.Cross(w).Unit();
+  v := w.Cross(u);
+
+  viewport_u := SplatVec3(viewport_width).Mul(u);
+  viewport_v := SplatVec3(viewport_height).Mul(v.Neg());
 
   cam.PDU = viewport_u.Div(SplatVec3(float64(cam.ImageWidth)));
   cam.PDV = viewport_v.Div(SplatVec3(float64(cam.ImageHeight)));
 
   viewport_upperleft := cam.Centre.
-                        Sub(Vec3{0, 0, focal_length}).
+                        Sub(SplatVec3(focal_length).Mul(w)).
                         Sub(viewport_u.Div(SplatVec3(2))).
                         Sub(viewport_v.Div(SplatVec3(2)));
   cam.Pixel00 = viewport_upperleft.
diff --git a/rtiaw.go b/rtiaw.go
index 1427fbf..25dd971 100644
--- a/rtiaw.go
+++ b/rtiaw.go
@@ -22,7 +22,10 @@ func main() {
   world.Add(Sphere{Vec3{-1.0,    0  , -1  },   0.4, mat_bubble});
   world.Add(Sphere{Vec3{ 1.0,    0  , -1  },   0.5, mat_right});
 
-  cam := NewCamera(400, 16.0/9.0, 100, 50);
+  cam := NewCamera(400, 16.0/9.0,
+                   100, 50,
+                   20, Vec3{-2, 2, 1},
+                   Vec3{0, 0, -1}, Vec3{0, 1, 0});
   cam.Render(world);
 
   dur := time.Since(start);
-- 
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