Basic implementation of the Mandelbrot fractal in Kotlin

MandelbrotSimple.kt

import java.awt.image.BufferedImage

  data class FractalParams(
      val width: Int,
      val height: Int,
      val maxIterations: Int = 256,
  )

  fun render(params: FractalParams): BufferedImage {
      val image = BufferedImage(params.width, params.height, BufferedImage.TYPE_INT_RGB)

      for (py in 0 until params.height) {
          for (px in 0 until params.width) {
              // Map pixel coordinates to the complex plane [-2, 2]
              val cx = (px - params.width / 2.0) / (params.width / 4.0) - 0.5
              val cy = (py - params.height / 2.0) / (params.height / 4.0)

              val iterations = iterate(cx, cy, params.maxIterations)

              // Black = inside the set, white = outside
              val color = if (iterations == params.maxIterations) 0x000000 else 0xFFFFFF
              image.setRGB(px, py, color)
          }
      }

      return image
  }

  // Returns the number of iterations before the sequence escapes,
  // or maxIterations if it never does (point is in the Mandelbrot set).
  fun iterate(cx: Double, cy: Double, maxIterations: Int): Int {
      var zx = 0.0
      var zy = 0.0
      var i = 0

      // The sequence z_{n+1} = z_n^2 + c diverges when |z| >= 2 (i.e. |z|^2 >= 4)
      while (i < maxIterations && zx * zx + zy * zy < 4.0) {
          val newZx = zx * zx - zy * zy + cx   // Re(z^2 + c)
          zy = 2.0 * zx * zy + cy              // Im(z^2 + c)
          zx = newZx
          i++
      }

      return i
  }