Sunday, July 12, 2020

android kotlin - Canvas erase drawing

MainActivity.kt

package com.cfsuman.kotlintutorials

import android.app.Activity
import android.graphics.*
import android.os.Bundle
import android.widget.ImageView
import kotlin.math.min


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)


        // show drawing on image view
        imageView.setImageBitmap(eraseDrawing())
    }
}



// function to erase / clear drawing from canvas
fun eraseDrawing():Bitmap?{
    val bitmap = Bitmap.createBitmap(
        1500,
        850,
        Bitmap.Config.ARGB_8888
    )


    // canvas for drawing
    val canvas = Canvas(bitmap).apply {
        drawColor(Color.parseColor("#A2A2D0"))
    }


    // draw a rectangle on canvas
    canvas.drawRect(
        100F,
        100F,
        canvas.width - 100F,
        canvas.height - 100F,
        Paint().apply { color = Color.parseColor("#333399") }
    )


    // paint to erase / clear drawing from canvas
    val paint = Paint().apply {
        isAntiAlias = true

        // destination pixels covered by
        // the source are cleared to 0
        xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)
    }


    // draw circle to erase / clear circular
    // area drawing from canvas
    canvas.drawCircle(
        canvas.width / 2F,
        canvas.height / 2F,
        min(canvas.width,canvas.height) / 2F - 25F,
        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"
    android:id="@+id/rootLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#DCDCDC"
    android:padding="24dp">

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

</androidx.constraintlayout.widget.ConstraintLayout>