func tracer(orig, dir vector.Vector) (st status, dist float64, bounce vector.Vector) {
dist = 1e9
st = missUpward
p := -orig.Z / dir.Z
if 0.01 < p {
dist = p
bounce = vector.Vector{X: 0, Y: 0, Z: 1}
st = missDownward
}
for i, _ := range objects {
p := orig.Add(objects[i])
b := p.DotProduct(dir)
c := p.DotProduct(p) - 1
b2 := b * b
if b2 > c {
q := b2 - c
s := -b - math.Sqrt(q)
if s < dist && s > 0.01 {
dist = s
bounce = p // We can lazy compute bounce based on value of p
st = hit
}
}
}
if st == hit {
bounce = bounce.Add(dir.Scale(dist)).Normalize()
}
return
}
func (r row) render(a, b, c vector.Vector, bytes []byte, seed *uint32) {
k := (*height - int(r) - 1) * 3 * *width
for x := (*width - 1); x >= 0; x-- {
p := vector.Vector{X: 13, Y: 13, Z: 13}
for i := 0; i < 64; i++ {
t := a.Scale(rnd(seed) - 0.5).Scale(99).Add(b.Scale(rnd(seed) - 0.5).Scale(99))
orig := vector.Vector{X: 17, Y: 16, Z: 8}.Add(t)
dir := t.Scale(-1).Add(a.Scale(rnd(seed) + float64(x)).Add(b.Scale(float64(r) + rnd(seed))).Add(c).Scale(16)).Normalize()
p = sampler(orig, dir, seed).Scale(3.5).Add(p)
}
bytes[k] = byte(p.X)
bytes[k+1] = byte(p.Y)
bytes[k+2] = byte(p.Z)
k += 3
}
}
func sampler(orig, dir vector.Vector, seed *uint32) vector.Vector {
st, dist, bounce := tracer(orig, dir)
obounce := bounce
if st == missUpward {
p := 1 - dir.Z
p = p * p
p = p * p
return vector.Vector{X: 0.7, Y: 0.6, Z: 1}.Scale(p)
}
h := orig.Add(dir.Scale(dist))
l := vector.Vector{X: 9 + rnd(seed), Y: 9 + rnd(seed), Z: 16}.Add(h.Scale(-1)).Normalize()
b := l.DotProduct(bounce)
sf := 1.0
if b < 0 {
b = 0
sf = 0
} else {
var st status
if st, dist, bounce = tracer(h, l); st != missUpward {
b = 0
sf = 0
}
}
if st == missDownward {
h = h.Scale(0.2)
fc := vector.Vector{X: 3, Y: 3, Z: 3}
if int(math.Ceil(h.X)+math.Ceil(h.Y))&1 == 1 {
fc = vector.Vector{X: 3, Y: 1, Z: 1}
}
return fc.Scale(b*0.2 + 0.1)
}
r := dir.Add(obounce.Scale(obounce.DotProduct(dir.Scale(-2))))
p := l.DotProduct(r.Scale(sf))
p33 := p * p // p ** 2
p33 = p33 * p33 // p ** 4
p33 = p33 * p33 // p ** 8
p33 = p33 * p33 // p ** 16
p33 = p33 * p33 // p ** 32
p33 = p33 * p // p ** 33
p = p33 * p33 * p33
return vector.Vector{X: p, Y: p, Z: p}.Add(sampler(h, r, seed).Scale(0.5))
}