From 2f025ebfc6c9e3146ef1c356f99045edc203c9ee Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Mon, 24 Jun 2024 16:50:36 +0100
Subject: Chapter 8

---
 camera.go   | 30 +++++++++++++++++++++++-------
 interval.go | 18 ++++++++++++++++++
 rtiaw.go    |  2 +-
 vec3.go     |  8 +++++---
 4 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/camera.go b/camera.go
index e460cc0..569d385 100644
--- a/camera.go
+++ b/camera.go
@@ -12,15 +12,18 @@ type Camera struct {
   PDU Vec3
   PDV Vec3
   Pixel00 Vec3
+  AntiAliasing uint
 }
 
-func NewCamera(w uint, ar float64) (cam Camera) {
+func NewCamera(w uint, ar float64, aa uint) (cam Camera) {
   cam.ImageWidth = w;
   cam.ImageHeight = uint(float64(cam.ImageWidth) / ar);
   if cam.ImageHeight < 1 {
     cam.ImageHeight = 1;
   }
 
+  cam.AntiAliasing = aa;
+
   focal_length := 1.0;
   viewport_height := 2.0;
   viewport_width := viewport_height *
@@ -51,14 +54,27 @@ func (cam Camera) Render(world Hittable) {
                 "Scanlines remaining: %3d...",
                 (cam.ImageHeight - row));
     for col := uint(0); col < cam.ImageWidth; col++ {
-      pixel_centre := cam.Pixel00.
-                      Add(cam.PDU.Mul(Splat(float64(col)))).
-                      Add(cam.PDV.Mul(Splat(float64(row))));
-      ray_direction := pixel_centre.Sub(cam.Centre);
-      ray := Ray{cam.Centre, ray_direction}
-      pixel_colour := ray.Colour(world);
+      pixel_colour := Splat(0);
+      for i := uint(0); i < cam.AntiAliasing; i++ {
+        r := cam.GetRay(row, col);
+        pixel_colour = pixel_colour.Add(r.Colour(world));
+      }
+      pixel_colour = pixel_colour.Div(Splat(float64(cam.AntiAliasing)));
       fmt.Printf("%s    ", pixel_colour.ToPPM());
     }
     fmt.Printf("\n");
   }
 }
+
+func (cam Camera) GetRay(row uint, col uint) Ray {
+  offset := unit_square();
+  pixel_sample := cam.Pixel00.
+                  Add(cam.PDU.Mul(Splat(float64(col) + offset.X))).
+                  Add(cam.PDV.Mul(Splat(float64(row) + offset.Y)));
+  return Ray{cam.Centre, pixel_sample.Sub(cam.Centre)};
+}
+
+func unit_square() Vec3 {
+  i := Interval{-0.5, 0.5};
+  return Vec3{i.Sample(), i.Sample(), 0};
+}
diff --git a/interval.go b/interval.go
index 5f44f51..763939a 100644
--- a/interval.go
+++ b/interval.go
@@ -1,5 +1,9 @@
 package main
 
+import (
+  "math/rand"
+)
+
 type Interval struct {
   Min float64
   Max float64
@@ -16,3 +20,17 @@ func (i Interval) Include(x float64) bool {
 func (i Interval) Surround(x float64) bool {
   return i.Min < x && x < i.Max;
 }
+
+func (i Interval) Clamp(x float64) float64 {
+  if x < i.Min {
+    return i.Min;
+  }
+  if x > i.Max {
+    return i.Max;
+  }
+  return x;
+}
+
+func (i Interval) Sample() float64 {
+  return rand.Float64() * i.Size() + i.Min;
+}
diff --git a/rtiaw.go b/rtiaw.go
index 03cee09..ec5975e 100644
--- a/rtiaw.go
+++ b/rtiaw.go
@@ -13,7 +13,7 @@ func main() {
   world.Add(Sphere{Vec3{0,    0  , -1},   0.5});
   world.Add(Sphere{Vec3{0, -100.5, -1}, 100  });
 
-  cam := NewCamera(400, 16.0/9.0);
+  cam := NewCamera(400, 16.0/9.0, 100);
   cam.Render(world);
 
   dur := time.Since(start);
diff --git a/vec3.go b/vec3.go
index 65d14e5..4212b46 100644
--- a/vec3.go
+++ b/vec3.go
@@ -53,9 +53,11 @@ func (v Vec3) Cross(w Vec3) Vec3 {
 }
 
 func (v Vec3) ToPPM() string {
-  r := uint8(255.999 * v.X);
-  g := uint8(255.999 * v.Y);
-  b := uint8(255.999 * v.Z);
+  i := Interval{0, 0.999};
+
+  r := uint8(256 * i.Clamp(v.X));
+  g := uint8(256 * i.Clamp(v.Y));
+  b := uint8(256 * i.Clamp(v.Z));
 
   return fmt.Sprintf("%3d %3d %3d", r, g, b);
 }
-- 
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