android kotlin - Bitmap add padding

MainActivity.kt


package com.cfsuman.kotlintutorials

import android.app.Activity
import android.content.Context
import android.graphics.*
import android.os.Bundle
import android.widget.*
import java.io.IOException

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

        // get the widgets reference from XML layout
        val imageView = findViewById<ImageView>(R.id.imageView)
        val imageView2 = findViewById<ImageView>(R.id.imageView2)
        val textView2 = findViewById<TextView>(R.id.textView2)


        // get the bitmap from assets folder
        val bitmap = assetsToBitmap("flower103.jpg")


        bitmap?.apply {
            // show original bitmap in first image view
            imageView.setImageBitmap(this)

            // add padding to bitmap
            // and keep bitmap transparency
            imageView2.setImageBitmap(addPadding(
                color = Color.parseColor("#F8F8F8"),
                left = 10,
                top = 20,
                right = 30,
                bottom = 40
            ))
            textView2.text = "Padding (10,20,30,40)"
        }
    }
}



// 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 add padding to bitmap
fun Bitmap.addPadding(
    color:Int = Color.GRAY,
    left:Int = 0,
    top:Int = 0,
    right:Int = 0,
    bottom:Int = 0
):Bitmap?{
    val bitmap = Bitmap.createBitmap(
        width + left + right, // width in pixels
        height + top + bottom, // height in pixels
        Bitmap.Config.ARGB_8888
    )

    val canvas = Canvas(bitmap)

    // draw solid color on full canvas area
    canvas.drawColor(color)

    // clear color from bitmap drawing area
    // this is very important for transparent bitmap borders
    // this will keep bitmap transparency
    Paint().apply {
        xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)
        canvas.drawRect(
            Rect(left,top,bitmap.width - right,
                bitmap.height - bottom),
            this
        )
    }

    // finally, draw bitmap on canvas
    Paint().apply {
        canvas.drawBitmap(
            this@addPadding, // bitmap
            0f + left, // left
            0f + top, // top
            this // paint
        )
    }

    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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/rootLayout"
    android:background="#DCDCDC"
    android:padding="24dp">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="250dp"
        android:layout_marginTop="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

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

    <ImageView
        android:id="@+id/imageView2"
        android:layout_width="0dp"
        android:layout_height="250dp"
        android:layout_marginTop="24dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

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

</androidx.constraintlayout.widget.ConstraintLayout>