Multiple samples per pixel + focus effect

src/main/kotlin/Ray.kt

@@ -42,14 +42,34 @@ fun main() {
 
     for (y in 0 until bmp.height) {
         for (x in 0 until bmp.width) {
-            val point = Point(x.toFloat(), y.toFloat(), 0f)
-            val ray = origin.rayTo(point)
+            var r = 0f
+            var g = 0f
+            var b = 0f
 
-            val color = scene.colorForRay(ray)
-            if (color != null) {
-                bmp.setPixel(x, y, color.toColor())
+            repeat(samplesPerPixel) {
+                val point = Point(x.toFloat(), y.toFloat(), 0f) + Vector.randomInCircleXY() * blurriness
+                val ray = origin.rayTo(point)
+
+                val color = scene.colorForRay(ray)
+                if (color != null) {
+                    r += color.r
+                    g += color.g
+                    b += color.b
+                }
             }
+
+            bmp.setPixel(
+                x, y,
+                MaterialColor(
+                    r = r / samplesPerPixel,
+                    g = g / samplesPerPixel,
+                    b = b / samplesPerPixel
+                ).toColor()
+            )
         }
     }
     File("test.tga").writeBitmap(bmp)
 }
+
+const val samplesPerPixel = 5
+const val blurriness = 1f

src/main/kotlin/math/Vector.kt

@@ -1,6 +1,9 @@
 package math
 
+import kotlin.math.cos
+import kotlin.math.sin
 import kotlin.math.sqrt
+import kotlin.random.Random
 
 data class Vector(val x: Float, val y: Float, val z: Float) {
     val length: Float get() = sqrt(squaredLength)
@@ -21,6 +24,14 @@ data class Vector(val x: Float, val y: Float, val z: Float) {
     )
 
     infix fun dot(rhs: Vector): Float = x * rhs.x + y * rhs.y + z * rhs.z
+
+    companion object {
+        fun randomInCircleXY(): Vector {
+            val r = sqrt(Random.Default.nextFloat())
+            val theta = Random.Default.nextFloat() * 2 * Math.PI.toFloat()
+            return Vector(r * sin(theta), r * cos(theta), 0f)
+        }
+    }
 }
 
 operator fun Float.times(rhs: Vector): Vector = rhs * this