Returns an Observable stream of screen grabs using java.awt.Robot. Uses multiple threads to get a somewhat reasonable FPS as per https://github.com/bahusvel/JavaScreenCapture

RxScreenCaptureSource.kt

fun getScreenCaptureSource(
    screenRectangle: Rectangle,
    numThreads: Int = 6,
    fpsPerThread: Int = 8,
    robot: Robot = Robot()
): Observable<BufferedImage> {
    val periodPerThreadMs: Long = 1000 / fpsPerThread.toLong()
    val perThreadOffsetMs: Long = periodPerThreadMs / numThreads

    val sources = (0 until numThreads).map { i ->
        val initialDelayMs = i * perThreadOffsetMs
        Observable.interval(initialDelayMs, periodPerThreadMs, TimeUnit.MILLISECONDS)
            .observeOn(Schedulers.newThread())
            .map { robot.createScreenCapture(screenRectangle) }
    }

    return Observable.merge(sources)
}