Glide v4 mask transformation. Supports vector drawables as mask drawable for transformation.

MaskImageTransformation.kt

import android.graphics.*
import android.graphics.drawable.Drawable
import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool
import com.bumptech.glide.load.resource.bitmap.BitmapTransformation
import java.io.UnsupportedEncodingException
import java.security.MessageDigest

class MaskImageTransformation(private val mask: Drawable) : BitmapTransformation() {

    override fun transform(pool: BitmapPool, toTransform: Bitmap, outWidth: Int, outHeight: Int): Bitmap {
        val width = toTransform.width
        val height = toTransform.height

        val bitmap = pool.get(width, height, Bitmap.Config.ARGB_8888)
        bitmap.setHasAlpha(true)

        val canvas = Canvas(bitmap)
        mask.setBounds(0, 0, width, height)
        mask.draw(canvas)
        canvas.drawBitmap(toTransform, 0f, 0f, paint)

        return bitmap
    }

    @Throws(UnsupportedEncodingException::class)
    override fun updateDiskCacheKey(messageDigest: MessageDigest) {
        messageDigest.update(ID_BYTES)
    }

    override fun hashCode(): Int {
        return ID.hashCode()
    }

    override fun equals(other: Any?): Boolean {
        return other is MaskImageTransformation
    }

    companion object {
        private val ID = "MaskImageTransformation"
        private val ID_BYTES = ID.toByteArray(charset(STRING_CHARSET_NAME))
        private val paint = Paint()

        init {
            paint.xfermode = PorterDuffXfermode(PorterDuff.Mode.SRC_IN)
        }
    }
}