A bitmap util that scale source bitmap to specific size with aspect ratio remained, alpha pixels filled on one dimension if need

BitmapUtils.java

public class BitmapUtils {

    /**
     * scale source bitmap to specific width and height remaining the aspect ratio.
     * If source bitmap aspect ratio is not the same with target ((float) dstWidth / dstHeight),
     * then one dimension will scaled to the target value, and another will be filled with 0 alpha pixels
     *
     * @param src       source bitmap
     * @param dstWidth  target width
     * @param dstHeight target height
     * @param filter    true if the source should be filtered.
     * @return target bitmap
     */
    public static Bitmap createScaledBitmapAspectRatioKept(Bitmap src, int dstWidth, int dstHeight, boolean filter) {
        final Bitmap dstBitmap = Bitmap.createBitmap(dstWidth, dstHeight, Bitmap.Config.ARGB_8888);
        final Canvas canvas = new Canvas(dstBitmap);

        final float srcWidth = src.getWidth();
        final float srcHeight = src.getHeight();

        final float xScale = dstWidth / srcWidth;
        final float yScale = dstHeight / srcHeight;
        final float scale = Math.min(xScale, yScale);

        final Matrix matrix = new Matrix();
        final float xTranslation;
        final float yTranslation;
        if (xScale < yScale) {
            xTranslation = 0.0f;
            yTranslation = (dstHeight - srcHeight * scale) / 2.0f;
        } else {
            xTranslation = (dstWidth - srcWidth * scale) / 2.0f;
            yTranslation = 0.0f;
        }
        matrix.postTranslate(xTranslation, yTranslation);
        matrix.preScale(scale, scale);

        Paint paint = new Paint();
        paint.setFilterBitmap(filter);
        paint.setAntiAlias(!matrix.rectStaysRect());
        canvas.drawBitmap(src, matrix, paint);

        return dstBitmap;
    }

}