Monday, June 29, 2020

android kotlin - Bitmap add border

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 the bitmap from assets folder
        val bitmap = assetsToBitmap("whiteDaisy.png")

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

            // add border to bitmap
            // and keep bitmap transparency
            imageView2.setImageBitmap(addBorder(
                color = Color.parseColor("#614051"),
                borderWidth = 20
            ))
            textView2.text = "Bitmap Border 20 px"
        }
    }
}


// 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 border to bitmap
fun Bitmap.addBorder(
    color:Int = Color.DKGRAY,
    borderWidth:Int = 10
):Bitmap?{
    val bitmap = Bitmap.createBitmap(
        width + borderWidth * 2, // width in pixels
        height + borderWidth * 2, // 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 border
    // this will keep bitmap transparency
    Paint().apply {
        xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)
        canvas.drawRect(
            Rect(
                borderWidth, // left
                borderWidth, // top
                bitmap.width - borderWidth, // right
                bitmap.height - borderWidth // bottom
            ),
            this
        )
    }

    // finally, draw bitmap on canvas
    Paint().apply {
        canvas.drawBitmap(
            this@addBorder, // bitmap
            0f + borderWidth, // left
            0f + borderWidth, // 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:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#F0EAD6"
    tools:context=".MainActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="0dp"
        android:layout_height="250dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="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="Transparent 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="250dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="12dp"
        android:layout_marginEnd="8dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        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="Bitmap Border"
        app:layout_constraintEnd_toEndOf="@+id/imageView2"
        app:layout_constraintStart_toStartOf="@+id/imageView2"
        app:layout_constraintTop_toBottomOf="@+id/imageView2" />

</androidx.constraintlayout.widget.ConstraintLayout>