Java port of https://stackoverflow.com/questions/16702966/rotate-image-and-crop-out-black-borders/16778797#16778797

rotatedRectWithMaxArea.java

//Given width and height of a rectangle which is rotated from center by angle in radians,
//returns width and height of rectangle to crop from center of original image to eliminate the black borders
// https://i.stack.imgur.com/KWoeo.jpg
//Similar to this image above,input params are input's width and height,rotation in radians
//Output is pair.first = width of cropped image in B, pair.second = height of cropped image in B
//You can use the scaleCenterCrop function to crop the image bitmap on android

// Usage:
// Pair<Integer, Integer> pair = rotatedRectWithMaxArea(originalImageWidth, originalImageHeight, Math.toRadians(rotation));

    public Pair<Integer,Integer> rotatedRectWithMaxArea(int w, int h, double angle){
        double height=0;
        double width=0;
        if(w<=0 || h<=0){
            return new Pair<>((int) width, (int) height);
        }

        int quadrant = (int) (Math.floor(angle / (Math.PI / 2))) & 3;
        double sign_alpha = ((quadrant & 1) == 0) ? angle : (Math.PI - angle);
        double alpha = (sign_alpha % Math.PI + Math.PI) % Math.PI;

        double bb_w = w * Math.cos(alpha) + h * Math.sin(alpha);
        double bb_h = w * Math.sin(alpha) + h * Math.cos(alpha);

        double gamma = (w < h) ? (Math.atan2(bb_w, bb_w)) : (Math.atan2(bb_w, bb_w));

        double delta = Math.PI - alpha - gamma;

        int length = (w < h) ? h : w;

        double d = length * Math.cos(alpha);
        double a = d * Math.sin(alpha) / Math.sin(delta);

        double y = a * Math.cos(gamma);
        double x = y * Math.tan(gamma);
        return new Pair<>((int)(bb_w - 2 * x),(int)(bb_h - 2 * y));
    }


    static public Bitmap scaleCenterCrop(Bitmap source,int newWidth, int newHeight) {
        float centerX = (newWidth  - source.getWidth()) * 0.5f;
        float centerY = (newHeight- source.getHeight()) * 0.5f;
        Bitmap dest = Bitmap.createBitmap(newWidth, newHeight,Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(dest);
        canvas.drawBitmap(source, centerX,centerY,new Paint());
        return dest;
    }