DepthPageTransformer

gistfile1.txt

class DepthPageTransformer: ViewPager.PageTransformer {
    companion object {
        private const val MIN_SCALE = 0.75f
    }

    override fun transformPage(view: View, position: Float) {
        when {
            position < -1 -> // [-Infinity,-1)
                // This page is way off-screen to the left.
                view.alpha = 0f
            position <= 0 ->  // [-1,0]
                // Use the default slide transition when moving to the left page
                view.apply {
                    alpha = 1f
                    translationX = 0f
                    scaleX = 1f
                    scaleY = 1f
                }
            position <= 1 ->  // (0,1]
                view.apply {
                    // Fade the page out.
                    alpha = 1 - position

                    // Counteract the default slide transition
                    translationX = width * -position

                    // Scale the page down (between MIN_SCALE and 1)
                    val scaleFactor = MIN_SCALE + (1 - MIN_SCALE) * (1 - Math.abs(position))
                    scaleX = scaleFactor
                    scaleY = scaleFactor
                }
            else -> // (1,+Infinity]
                // This page is way off-screen to the right.
                view.alpha = 0f
        }
    }
}