android kotlin - ImageView rounded top corners programmatically

MainActivity.kt


package com.example.jetpack

import android.content.Context
import android.graphics.*
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import java.io.IOException


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

        // get bitmap from assets
        val bitmap: Bitmap? = assetsToBitmap("flower.jpg")

        // set the image view image from assets
        bitmap?.apply {
            imageView.setImageBitmap(this)
        }

        // make the bitmap rounded top corners
        button.setOnClickListener {
            bitmap?.toRoundedCorners(
                topLeftRadius = 150F,
                topRightRadius = 150F
            )?.apply {
                // show the rounded top corners bitmap in image view
                imageView.setImageBitmap(this)
            }
        }
    }
}


// extension function to make rounded corners bitmap
fun Bitmap.toRoundedCorners(
    topLeftRadius: Float = 0F,
    topRightRadius: Float = 0F,
    bottomRightRadius: Float = 0F,
    bottomLeftRadius: Float = 0F
):Bitmap?{
    val bitmap = Bitmap.createBitmap(
        width, // width in pixels
        height, // height in pixels
        Bitmap.Config.ARGB_8888
    )
    val canvas = Canvas(bitmap)

    // the bounds of a round-rectangle to add to the path
    val rectF = RectF(0f,0f,width.toFloat(),height.toFloat())

    // float array of 8 values, 4 pairs of [x,y] radii
    val radii = floatArrayOf(
        topLeftRadius,topLeftRadius, // top left corner
        topRightRadius,topRightRadius, // top right corner
        bottomRightRadius,bottomRightRadius, // bottom right corner
        bottomLeftRadius,bottomLeftRadius // bottom left corner
    )

    // path to draw rounded corners bitmap
    val path = Path().apply {
        // add a closed round-rectangle contour to the path
        // each corner receives two radius values [x, y]
        addRoundRect(
            rectF,
            radii,
            // the direction to wind the round-rectangle's contour
            Path.Direction.CCW
        )
    }

    // intersect the current clip with the specified path
    canvas.clipPath(path)

    // draw the rounded corners bitmap on canvas
    canvas.drawBitmap(this,0f,0f,null)
    return bitmap
}


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

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"
    android:background="#EDEAE0"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="Round Top Corners"
        android:backgroundTint="#333399"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="250dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="12dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button"
        tools:srcCompat="@tools:sample/avatars" />

</androidx.constraintlayout.widget.ConstraintLayout>