1 files changed, 87 insertions, 0 deletions
diff --git a/hittable.go b/hittable.go
new file mode 100644
index 0000000..5320a0f
--- /dev/null
+++ b/hittable.go
@@ -0,0 +1,87 @@
+package main
+
+import (
+  maths "math"
+)
+
+//HitRecord
+
+type HitRecord struct {
+  Valid bool
+  P Vec3
+  N Vec3
+  T float64
+}
+
+func (rec *HitRecord) SetFaceNormal(r Ray, out_n Vec3) {
+  if r.Direction.Dot(out_n) < 0 {
+    rec.N = out_n
+  } else {
+    rec.N = out_n.Neg();
+  }
+}
+
+//Hittable
+
+type Hittable interface {
+  Hit(r Ray, ray_t Interval) (rec HitRecord)
+}
+
+//Sphere < Hittable
+
+type Sphere struct {
+  Origin Vec3
+  Radius float64
+}
+
+func (s Sphere) Hit(r Ray, ray_t Interval) (rec HitRecord) {
+  oc := s.Origin.Sub(r.Origin);
+  a := r.Direction.MagSqr();
+  h := r.Direction.Dot(oc);
+  c := oc.MagSqr() - maths.Pow(s.Radius, 2);
+  disc := maths.Pow(h, 2) - a*c;
+
+  if disc < 0 {
+    return;
+  }
+
+  sqrtd := maths.Sqrt(disc);
+  root := (h - sqrtd) / a;
+  if !ray_t.Surround(root) {
+    root = (h + sqrtd) / a;
+    if !ray_t.Surround(root) {
+      return;
+    }
+  }
+
+  rec.T = root;
+  rec.P = r.At(rec.T);
+  out_n := rec.P.Sub(s.Origin).Div(Splat(s.Radius));
+  rec.SetFaceNormal(r, out_n);
+  rec.Valid = true;
+  return;
+}
+
+//Hittables < Hittable
+
+type Hittables struct {
+  Objects []Hittable
+}
+
+func (l *Hittables) Add(o Hittable) {
+  l.Objects = append(l.Objects, o);
+}
+
+func (l Hittables) Hit(r Ray, ray_t Interval) (rec HitRecord) {
+  closest_so_far := ray_t.Max;
+
+  for _, o := range l.Objects {
+    temp_rec := o.Hit(r, Interval{ray_t.Min, closest_so_far});
+    if temp_rec.Valid {
+      rec = temp_rec;
+      closest_so_far = rec.T;
+    }
+  }
+
+  return;
+}