From 438b1e9105aa0b34a5f41afacc6a5bfa29cbca73 Mon Sep 17 00:00:00 2001
From: Luxdragon <kopse@e.email>
Date: Mon, 12 Feb 2024 13:05:10 +0100
Subject: [PATCH] Implemented fast inverse square

---
 main.go | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/main.go b/main.go
index 634b79b..0400c38 100644
--- a/main.go
+++ b/main.go
@@ -3,6 +3,7 @@ package main
 import "fmt" // for IO and standard library
 import "os" // for handling the progress bar
 import "math" // for maths
+import "unsafe"
 
 // ================ VEC3 CLASS =====================
 
@@ -93,8 +94,16 @@ func Cross(v1 Vec3, v2 Vec3) Vec3 {
 		v1.E[0]*v2.E[1] - v1.E[1]*v2.E[0])
 }
 
+func q_rsqrt(v Vec3) float32 {
+	var x float32 = v.E[0]*v.E[0] + v.E[1]*v.E[1] + v.E[2]*v.E[2]
+	i := *(*int32)(unsafe.Pointer(&x)) // evil floating point bit level hacking
+    i = 0x5f3759df - (i >> 1)          // what the fuck?
+    y := *(*float32)(unsafe.Pointer(&i))
+    return y
+}
+
 func Unit_vector(v Vec3) Vec3 {
-	new_v := v.Div(v.Length())
+	new_v := v.Mult(q_rsqrt(v))
     return new_v
 }
 
@@ -141,8 +150,10 @@ func (r *Ray) At(t float32) Vec3 {
 }
 
 func Ray_color(r *Ray) Vec3 {
-	if (hit_sphere(NewPoint3(0,0,-1), 0.5, r)) {
-		return NewColor(1, 0, 0)
+	var t float32 = hit_sphere(NewPoint3(0,0,-1), 0.5, r)
+	if (t > 0.0) {
+		N := Unit_vector(r.At(t).Sub(NewVec3(0,0,-1)))
+		return NewColor(N.X()+1, N.Y()+1, N.Z()+1).Mult(0.5)
 	}
 	
 	unit_direction := Unit_vector(r.Direction())
@@ -153,16 +164,16 @@ func Ray_color(r *Ray) Vec3 {
 
 // =============== SPHERE ===================
 
-func hit_sphere(center Vec3, radius float32, r *Ray) bool {
+func hit_sphere(center Vec3, radius float32, r *Ray) float32 {
 	oc := r.Origin().Sub(center)
 	a := Dot(r.Direction(), r.Direction())
 	b := Dot(oc, r.Direction()) * 2.0
 	c := Dot(oc, oc) - radius*radius
 	discriminant := b*b - 4*a*c
-	if discriminant >= 0 {
-		return true
+	if (discriminant < 0) {
+		return -1.0
 	} else {
-		return false
+		return (-b-float32(math.Sqrt(float64(discriminant)))) / (2.0*a)
 	}
 }