Use infix dot product function.

src/main/kotlin/Plane.kt

@@ -1,8 +1,8 @@
 data class Plane(val point: Point, val normal: Vector, val material: Material) : Thing {
     override fun intersects(ray: Ray): Hit? {
-        val bottom = dot(normal, ray.direction)
+        val bottom = normal dot ray.direction
         if (bottom == 0.0f) return null
-        val t = dot(normal, point - ray.origin) / bottom
+        val t = (normal dot point - ray.origin) / bottom
         if (t <= 0.0f) return null
         return Hit(ray.at(t), normal, t, material)
     }

src/main/kotlin/Ray.kt

@@ -7,8 +7,6 @@ data class Ray(val origin: Point, val direction: Vector) {
 }
 
 
-fun dot(lhs: Vector, rhs: Vector): Float = lhs.x * rhs.x + lhs.y * rhs.y + lhs.z * rhs.z
-
 fun main() {
     val bmp = Bitmap(1000, 1000)
     val origin = Point(500f, 500f, -500f)

src/main/kotlin/ReflectiveMaterial.kt

@@ -13,7 +13,7 @@ data class ReflectiveMaterial(
         val rayToLight = offsetPoint.rayTo(light.point)
         if (scene.intersects(rayToLight) == null) {
 
-            val lambert = java.lang.Float.max(0f, dot(hit.normal, rayToLight.direction))
+            val lambert = java.lang.Float.max(0f, hit.normal dot rayToLight.direction)
             color += lambert * light.color
 
             val h = (-ray.direction + rayToLight.direction).normalized()

src/main/kotlin/Sphere.kt

@@ -4,7 +4,7 @@ import kotlin.math.sqrt
 data class Sphere(val center: Point, val radius: Float, val material: Material) : Thing {
     override fun intersects(ray: Ray): Hit? {
         val l = center - ray.origin
-        val tc = dot(l, ray.direction)
+        val tc = l dot ray.direction
         if (tc < 0f) return null
 
         val d = l.squaredLength - tc * tc

src/main/kotlin/WhateverMaterial.kt

@@ -10,12 +10,12 @@ data class WhateverMaterial(val color: MaterialColor,
         val rayToLight = (hit.point + 0.0001f * hit.normal).rayTo(light.point)
         if (scene.intersects(rayToLight) == null) {
 
-            val lambert = java.lang.Float.max(0f, dot(hit.normal, rayToLight.direction))
+            val lambert = java.lang.Float.max(0f, hit.normal dot rayToLight.direction)
             color += lambert * light.color
 
             val h = (-ray.direction + rayToLight.direction).normalized()
 
-            val intensity = dot(hit.normal, h).pow(specular)
+            val intensity = (hit.normal dot h).pow(specular)
 
             color += intensity * MaterialColor(0.3f, 0f, 0f)
         }