object.go

package main

// Hittable is an interface representing something that can be hit by rays.  It
// can be a single item like a Sphere or a group of objects like the World
// (array of Spheres).
type Hittable interface {
	Hit(ray *Ray, min, max float64) (bool, *HitRecord)
}

// Hit Record stores information about a specific intersect of a ray hitting a
// Hittable object.
type HitRecord struct {
	point     Vec3
	normal    Vec3
	t         float64
	frontFace bool

	material Material
}

func (r *HitRecord) SetFaceNormal(ray *Ray, outwardNormal Vec3) {
	r.frontFace = ray.direction.Dot(outwardNormal) < 0
	if r.frontFace {
		r.normal = outwardNormal
	} else {
		r.normal = outwardNormal.Neg()
	}
}

// World is an array of hittable objects (Spheres, etc) that implement the
// Hittable interface. It handles the z-index to know what to draw in front.

type World []Hittable

func (w World) Hit(ray *Ray, tMin, tMax float64) (bool, *HitRecord) {
	tempRecord := &HitRecord{}
	hitAnything := false
	closestSoFar := tMax

	for _, object := range w {
		hit, record := object.Hit(ray, tMin, closestSoFar)
		if hit {
			hitAnything = true
			closestSoFar = record.t
			tempRecord = record
		}
	}
	return hitAnything, tempRecord
}