android kotlin - Bitmap change opacity

MainActivity.kt

package com.example.jetpack

import android.content.Context
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.graphics.Canvas
import android.graphics.PorterDuff
import android.os.Bundle
import android.widget.SeekBar
import android.widget.SeekBar.OnSeekBarChangeListener
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import java.io.IOException
import kotlin.math.roundToInt


class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // get the bitmap from assets folder
        val bitmap = assetsToBitmap("blueFlower.png")

        bitmap?.apply {
            // show original bitmap in first image view
            imageView.setImageBitmap(this)
            textView.text = "Original Bitmap"

            seekBar.setOnSeekBarChangeListener(object : OnSeekBarChangeListener {
                override fun onProgressChanged(
                    seekBar: SeekBar?,
                    progress: Int,
                    fromUser: Boolean
                ) {
                    // show the transparent bitmap in image view
                    imageView2.setImageBitmap(setOpacity(progress))
                    textView2.text = "Bitmap Opacity $progress%"
                    textView2.append("\n0% full transparent 100% full opaque")

                    val alpha = (progress * 2.55).roundToInt()
                    textView2.append("\nAlpha value $alpha (Range 0..255)")
                }

                override fun onStartTrackingTouch(seekBar: SeekBar?) {
                }

                override fun onStopTrackingTouch(seekBar: SeekBar?) {
                }
            })
        }
    }
}


// extension function to get bitmap from assets
fun Context.assetsToBitmap(fileName:String):Bitmap?{
    return try {
        val stream = assets.open(fileName)
        BitmapFactory.decodeStream(stream)
    } catch (e: IOException) {
        e.printStackTrace()
        null
    }
}


// extension function to set bitmap opacity by percent
fun Bitmap.setOpacity(opacityPercent:Int):Bitmap?{
    val bitmap = copy(Bitmap.Config.ARGB_8888,true)

    // int: set the alpha component [0..255] of the paint's color.
    // 0 is full transparent
    // 255 is full opaque
    val opacity = (opacityPercent * 2.55).roundToInt()
    val color = opacity and 0xFF shl 24

    Canvas(bitmap).drawColor(color, PorterDuff.Mode.DST_IN)
    return bitmap
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="200dp"
        android:layout_marginTop="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:srcCompat="@tools:sample/avatars" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="8dp"
        android:text="Original Bitmap"
        app:layout_constraintEnd_toEndOf="@+id/imageView"
        app:layout_constraintStart_toStartOf="@+id/imageView"
        app:layout_constraintTop_toBottomOf="@+id/imageView" />

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="0dp"
        android:layout_height="200dp"
        android:layout_marginTop="24dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        tools:srcCompat="@tools:sample/avatars" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="8dp"
        android:text="Transparent Bitmap"
        android:gravity="center_horizontal"
        app:layout_constraintEnd_toEndOf="@+id/imageView2"
        app:layout_constraintStart_toStartOf="@+id/imageView2"
        app:layout_constraintTop_toBottomOf="@+id/imageView2" />

    <SeekBar
        android:id="@+id/seekBar"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:max="100"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

</androidx.constraintlayout.widget.ConstraintLayout>