Add plane at bottom

src/Ray.kt

@@ -4,7 +4,7 @@ import kotlin.math.min
 import kotlin.math.pow
 import kotlin.math.sqrt
 
-data class Hit(val point: Point, val normal: Vector, val color: MaterialColor)
+data class Hit(val point: Point, val normal: Vector, val distance: Float, val color: MaterialColor)
 
 data class MaterialColor(val r: Float, val g: Float, val b: Float) {
     fun toColor(): Color = Color(
@@ -16,14 +16,30 @@ data class MaterialColor(val r: Float, val g: Float, val b: Float) {
     operator fun times(rhs: MaterialColor) = MaterialColor(r * rhs.r, g * rhs.g, b * rhs.b)
     operator fun plus(rhs: MaterialColor) = MaterialColor(r + rhs.r, g + rhs.g, b + rhs.b)
 }
+
 operator fun Float.times(rhs: MaterialColor) = MaterialColor(this * rhs.r, this * rhs.g, this * rhs.b)
 
 data class Ray(val origin: Point, val direction: Vector) {
     fun at(t: Float) = origin + t * direction
 }
 
-data class Sphere(val center: Point, val radius: Float, val color: MaterialColor) {
-    fun intersects(ray: Ray): Hit? {
+interface Thing {
+    fun intersects(ray: Ray): Hit?
+}
+
+
+data class Plane(val point: Point, val normal: Vector, val color: MaterialColor) : Thing {
+    override fun intersects(ray: Ray): Hit? {
+        val bottom = dot(normal, ray.direction)
+        if (bottom == 0.0f) return null
+        val t = dot(normal, point - ray.origin) / bottom
+        if (t <= 0.0f) return null
+        return Hit(ray.at(t), normal, t, color)
+    }
+}
+
+data class Sphere(val center: Point, val radius: Float, val color: MaterialColor) : Thing {
+    override fun intersects(ray: Ray): Hit? {
         val l = center - ray.origin
         val tc = dot(l, ray.direction)
         if (tc < 0f) return null
@@ -37,9 +53,8 @@ data class Sphere(val center: Point, val radius: Float, val color: MaterialColor
 
         val t = min(tc - thc, tc + thc)
 
-
         val hitPoint = ray.at(t)
-        return Hit(hitPoint, (hitPoint - center).normalized(), color)
+        return Hit(hitPoint, (hitPoint - center).normalized(), t, color)
     }
 }
 
@@ -47,11 +62,32 @@ fun dot(lhs: Vector, rhs: Vector): Float = lhs.x * rhs.x + lhs.y * rhs.y + lhs.z
 
 data class PointLight(val point: Point, val color: MaterialColor)
 
+data class Scene(val things: List<Thing>): Thing {
+    override fun intersects(ray: Ray): Hit? {
+        var closest: Hit? = null
+        for (thing in things) {
+            val hit = thing.intersects(ray)
+            if (hit != null && (closest == null || hit.distance < closest.distance)) {
+                closest = hit
+            }
+        }
+
+        return closest
+    }
+}
+
 fun main() {
     val bmp = Bitmap(1000, 1000)
     val origin = Point(500f, 500f, -500f)
 
     val sphere = Sphere(Point(500f, 500f, 500f), radius = 500f, color = MaterialColor(0f, 1.0f, 0f))
+    val plane = Plane(
+        Point(0f, -500f, 0f),
+        normal = Vector(0f, 1f, 0f),
+        color = MaterialColor(0.5f, 0.5f, 0.5f)
+    )
+
+    val scene = Scene(listOf(sphere, plane))
 
     val ambient = MaterialColor(0.1f, 0.1f, 0.1f)
 
@@ -63,12 +99,12 @@ fun main() {
             val point = Point(x.toFloat(), y.toFloat(), 0f)
             val ray = origin.rayTo(point)
 
-            val hit = sphere.intersects(ray)
+            val hit = scene.intersects(ray)
             if (hit != null) {
                 var color = hit.color * ambient
 
                 val rayToLight = hit.point.rayTo(light.point)
-                if (sphere.intersects(rayToLight) == null) {
+                if (scene.intersects(rayToLight) == null) {
 
                     val lambert = max(0f, dot(hit.normal, rayToLight.direction))
                     color += lambert * light.color