Canvas draw bitmap?

Question

I know that to draw bitmap in canvas we need to call canvas.drawBitmap(filterBitmap, 0f, 0f, paint) for full screen image. But I couldn't understand why my code didn't work and my ImageView is empty.

class MainActivity : AppCompatActivity() {

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

    val bitmap = BitmapFactory.decodeResource(resources, R.drawable.grass)
    val filterBitmap = Bitmap.createBitmap(bitmap.width, bitmap.height, bitmap.config)

    val paint = Paint().apply {
        color = Color.RED
        style = Paint.Style.FILL
    }
    val canvas = Canvas(filterBitmap)
    canvas.drawBitmap(filterBitmap, 0f, 0f, paint)
    filter_image.setImageBitmap(filterBitmap)
}

Drawable resource has width and height.

Eugene Surkov Eugene Surkov · Accepted Answer · 2017-07-30T21:24:41

Solution is draw rect with bitmap size and set some clor.

class MainActivity : AppCompatActivity() {

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

    val bitmap = BitmapFactory.decodeResource(resources, R.drawable.grass)
    val filterBitmap = Bitmap.createBitmap(bitmap.width, bitmap.height, bitmap.config)

    button.setOnClickListener {
        val paint = Paint().apply {
            color = Color.RED
        }
        val canvas = Canvas(filterBitmap)
        canvas.drawRect(Rect(/*bitmap size**/), Paint())
        filter_image.setImageBitmap(filterBitmap)
    }
}

} In this case

val filterBitmap = Bitmap.createBitmap(bitmap.width, bitmap.height, bitmap.config)

we have something like transparent bitmap

or use

filterBitmap.eraseColor(Color.RED)

Canvas draw bitmap?

1 Answers