Android - in Android Pie (API 28) RadialGradient draws a rectangle instead of a circle

I'm trying to simulate a TorchView with a background image and a foreground image. It works well on API 27 and below but draw a rectangle on API 28.

Any idea why it doesn't work on Android Pie ?

Screenshot on API 27 and below

Screenshot on API 28

Torch View class

class TorchView : View, OnTouchListener {

    var mBitmapBackground: Bitmap? = null
    var mBitmapForeground: Bitmap? = null
    var mMask: Bitmap? = null
    private var mPosX = 0f
    private var mPosY = 0f

    private lateinit var paintMask: Paint
    private lateinit var paintBackground: Paint
    private lateinit var paintForeground: Paint

    private var radius = 150


    constructor(context: Context) : super(context) {
        init()
    }

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {
        init()
    }


    fun initBitmaps(bitmapBackground: Bitmap, bitmapForeground: Bitmap, radius: Int){
        this.radius = radius
        mBitmapBackground = bitmapBackground
        mBitmapForeground = bitmapForeground
        mMask = makeRadGrad()
        mPosX = (bitmapBackground.width/2 - radius).toFloat()
        mPosY = (bitmapBackground.height/2 - radius).toFloat()
        invalidate()
    }

    fun init() {
        paintBackground = Paint()

        paintMask = Paint()
        paintMask.xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)

        paintForeground = Paint()
        paintForeground.xfermode = PorterDuffXfermode(PorterDuff.Mode.DST_OVER)

        isFocusable = true
        isFocusableInTouchMode = true
        this.setOnTouchListener(this)
    }

    public override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        val mask = mMask
        val bitmapForeground = mBitmapBackground
        val bitmapBackground = mBitmapForeground
        if(mask != null && bitmapForeground != null && bitmapBackground != null){
            canvas.save()
            canvas.drawBitmap(bitmapBackground, 0f, 0f, paintBackground)
            canvas.drawBitmap(mask, mPosX, mPosY, paintMask)
            canvas.drawBitmap(bitmapForeground, 0f, 0f, paintForeground)
            canvas.restore()
        }
    }

    private fun makeRadGrad(): Bitmap {
        val gradient = RadialGradient(
            radius.toFloat(), radius.toFloat(), radius.toFloat(), -0xff0100,
            0x00000000, android.graphics.Shader.TileMode.CLAMP
        )
        val p = Paint()
        p.isDither = true
        p.shader = gradient

        val bitmap = Bitmap.createBitmap(radius*2, radius*2, Config.ARGB_8888)
        val c = Canvas(bitmap)
        c.drawCircle(radius.toFloat(), radius.toFloat(), radius.toFloat(), p)

        return bitmap
    }

    override fun onTouch(v: View?, event: MotionEvent): Boolean {
        mPosX = event.x - radius
        mPosY = event.y - radius
        invalidate()
        return true
    }
}

from Android - in Android Pie (API 28) RadialGradient draws a rectangle instead of a circle