shadow.kt

private var shadow: Bitmap? = null
private val shadowPaint = Paint(ANTI_ALIAS_FLAG)

private var shadowRadius = context.resources.getDimension(R.dimen.shadow_default_radius)
private var shadowXOffset = context.resources.getDimension(R.dimen.shadow_default_x_translation)
private var shadowYOffset = context.resources.getDimension(R.dimen.shadow_default_y_translation)
private var shadowColor = ContextCompat.getColor(context, R.color.shadow_default_color)

private lateinit var shadowView: ImageView

private fun generateShadow() {
    shadow = Bitmap.createBitmap(shadowView.width, shadowView.height, Bitmap.Config.ALPHA_8)
    shadowPaint.apply {
        colorFilter = PorterDuffColorFilter(shadowColor,       PorterDuff.Mode.SRC_IN)
        setShadowLayer(shadowRadius, shadowXOffset, shadowYOffset, shadowColor)
    }
    val c = Canvas(shadow)
    shadowPath.let { path->
        c.drawPath(path, shadowPaint)
        shadowView.setImageBitmap(shadow)
        isShadowDirty = false
    }
}