AirBrush Medium article example

TinyThumbDecoder.kt

class TinyThumbDecoder(
    private var context: Context,
    private val bitmapPool: BitmapPool,
    private val blurProvider: (source: Bitmap, options: BlurOptions?) -> Bitmap
) : ResourceDecoder<TinyThumb, BitmapDrawable> {

    override fun handles(source: TinyThumb, options: Options) = source.base64.isNotEmpty()

    override fun decode(
        source: TinyThumb,
        width: Int,
        height: Int,
        options: Options
    ): Resource<BitmapDrawable>? {
        // Down sample the blurred bitmap to save resources. 
        // The later hardware upscale will look almost identical anyway.
        val sampleSize = source.options?.sampleSize?.coerceAtLeast(1) ?: 6
        val bitmap = generateBitmap(source, width / sampleSize, height / sampleSize)

        val bitmapResource = BitmapResource.obtain(bitmap, bitmapPool)
        return LazyBitmapDrawableResource.obtain(context.resources, bitmapResource)
    }
    
    private fun generateBitmap(thumb: TinyThumb, width: Int, height: Int): Bitmap {
        // This is application specific and must match how it was encoded
        val decodeFlag = Base64.URL_SAFE 
        val bytes = Base64.decode(thumb.base64, decodeFlag)

        val options = BitmapFactory.Options().apply {
            // RGB565 will take less memory, but the resulting gradient is horrible.
            inPreferredConfig = Bitmap.Config.ARGB_8888
        }
        // Convert the byte array into a bitmap.
        val source = requireNotNull(BitmapFactory.decodeByteArray(bytes, 0, bytes.size, options)) {
            "Failed to decode byte array. This can happen if the decode flag does not match the flag the data was encoded with."
        }

        // If the thumb is square or landscape, center crop it. Otherwise leave it as is.
        val centerCrop = crop(source, width, height, 0.5f, 1f)
        return blurProvider(centerCrop, thumb.options).also { centerCrop.recycle() }
    }

    /**
     * Returns a new Bitmap (from the pool) with a crop effect depending on the crop anchor given. 
     * 0.5f is like [android.widget.ImageView.ScaleType.CENTER_CROP]. The crop anchor will be be nudged
     * so the entire cropped bitmap will fit inside the src. May return the input bitmap if no
     * scaling is necessary.
     */
    private fun crop(
        source: Bitmap,
        width: Int,
        height: Int,
        horizontalCenterPercent: Float,
        verticalCenterPercent: Float
    ): Bitmap = TODO("Beyond the scope of this article")
}