Tuesday, July 14, 2020

android kotlin - Paint linear gradient

MainActivity.kt

package com.cfsuman.kotlintutorials

import android.app.Activity
import android.graphics.*
import android.os.Bundle
import android.widget.*


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(
            drawLinearGradient()
        )
    }
}



// function to draw linear gradient on canvas
fun drawLinearGradient():Bitmap?{
    val bitmap = Bitmap.createBitmap(
        1500,
        850,
        Bitmap.Config.ARGB_8888
    )


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


    // initialize a rectF instance
    val margin = 50F
    val rectF = RectF(
        margin, // left
        margin, // top
        canvas.width - margin, // right
        canvas.height - margin // bottom
    )


    // paint to draw linear gradient
    val paint = Paint().apply {
        isAntiAlias = true
        style = Paint.Style.FILL

        // linear gradient shader
        shader = LinearGradient(
            // x0, x-coordinate for the start of the gradient line
            0F,
            // y0,  y-coordinate for the start of the gradient line
            0F,
            // x1,  x-coordinate for the end of the gradient line
            rectF.width(),
            // y1, y-coordinate for the end of the gradient line
            rectF.height(),
            // color0, sRGB color at the start of the gradient line
            Color.parseColor("#00CC99"),
            // color1, sRGB color at the end of the gradient line
            Color.parseColor("#E30022"),
            // shader tiling mode
            Shader.TileMode.MIRROR
        )
    }


    // finally, draw linear gradient rectangle on canvas
    canvas.drawRect(rectF, 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: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="wrap_content"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>