Custom TextView that fades the final part of the text on the last line. maxLines attribute is required

FadeOutTextView.kt

import android.content.Context
import android.graphics.*
import android.support.v7.widget.AppCompatTextView
import android.text.Layout
import android.util.AttributeSet

class FadeOutTextView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttribute: Int = android.R.attr.textViewStyle
) : AppCompatTextView(context, attrs, defStyleAttribute) {

    companion object {
        private const val FADE_LENGTH = 3
    }

    private val shader: Shader
    private val mMatrix: Matrix = Matrix()
    private val paint: Paint = Paint()
    private val bounds: Rect = Rect()

    init {
        shader = LinearGradient(0f, 0f, 1f, 0f, 0, -0x1000000, Shader.TileMode.CLAMP)
        paint.shader = shader
        paint.xfermode = PorterDuffXfermode(PorterDuff.Mode.DST_OUT)
    }

    override fun onDraw(canvas: Canvas) {

        val layout = layout
        val line = maxLines - 1
        val isRtl = layout.getParagraphDirection(line) == Layout.DIR_RIGHT_TO_LEFT

        getLineBounds(line, bounds)

        val fadeLength = bounds.width() / FADE_LENGTH

        if (isRtl) {
            bounds.right = bounds.left + fadeLength
        } else {
            bounds.left = bounds.right - fadeLength
        }

        val saveCount = canvas.saveLayer(0f, 0f, width.toFloat(), height.toFloat(), null)
        super.onDraw(canvas)

        // Adjust and set the Shader Matrix
        mMatrix.reset()
        mMatrix.setScale(fadeLength.toFloat(), 1f)
        if (isRtl) {
            matrix.postRotate(180f, fadeLength / 2f, 0f)
        }
        mMatrix.postTranslate(bounds.left.toFloat(), 0f)
        shader.setLocalMatrix(mMatrix)

        canvas.drawRect(bounds, paint)
        canvas.restoreToCount(saveCount)

    }
}