private void fitImageToView() {
        Drawable drawable = getDrawable();
        if (drawable == null || drawable.getIntrinsicWidth() == 0 || drawable.getIntrinsicHeight() == 0) {
            return;
        }
        if (matrix == null || prevMatrix == null) {
            return;
        }

        int drawableWidth = drawable.getIntrinsicWidth();
        int drawableHeight = drawable.getIntrinsicHeight();

        //
        // Scale image for view
        //
        float scaleX = (float) viewWidth / drawableWidth;
        float scaleY = (float) viewHeight / drawableHeight;

        switch (mScaleType) {
            case CENTER:
                scaleX = scaleY = 1;
                break;

            case CENTER_CROP:
                scaleX = scaleY = Math.max(scaleX, scaleY);
                break;

            case CENTER_INSIDE:
                scaleX = scaleY = Math.min(1, Math.min(scaleX, scaleY));

            case FIT_CENTER:
                scaleX = scaleY = Math.min(scaleX, scaleY);
                break;

            case FIT_XY:
                break;

            default:
                //
                // FIT_START and FIT_END not supported
                //
                throw new UnsupportedOperationException("TouchImageView does not support FIT_START or FIT_END");

        }

        //
        // Center the image
        //
        float redundantXSpace = viewWidth - (scaleX * drawableWidth);
        float redundantYSpace = viewHeight - (scaleY * drawableHeight);
        matchViewWidth = viewWidth - redundantXSpace;
        matchViewHeight = viewHeight - redundantYSpace;
        if (!isZoomed() && !imageRenderedAtLeastOnce) {
            //
            // Stretch and center image to fit view
            //
            matrix.setScale(scaleX, scaleY);
            matrix.postTranslate(redundantXSpace / 2, redundantYSpace / 2);
            normalizedScale = 1;

        } else {
            //
            // These values should never be 0 or we will set viewWidth and viewHeight
            // to NaN in translateMatrixAfterRotate. To avoid this, call savePreviousImageValues
            // to set them equal to the current values.
            //
            if (prevMatchViewWidth == 0 || prevMatchViewHeight == 0) {
                savePreviousImageValues();
            }

            prevMatrix.getValues(m);

            //
            // Rescale Matrix after rotation
            //
            m[Matrix.MSCALE_X] = matchViewWidth / drawableWidth * normalizedScale;
            m[Matrix.MSCALE_Y] = matchViewHeight / drawableHeight * normalizedScale;

            //
            // TransX and TransY from previous matrix
            //
            float transX = m[Matrix.MTRANS_X];
            float transY = m[Matrix.MTRANS_Y];

            //
            // Width
            //
            float prevActualWidth = prevMatchViewWidth * normalizedScale;
            float actualWidth = getImageWidth();
            translateMatrixAfterRotate(Matrix.MTRANS_X, transX, prevActualWidth, actualWidth, prevViewWidth, viewWidth, drawableWidth);

            //
            // Height
            //
            float prevActualHeight = prevMatchViewHeight * normalizedScale;
            float actualHeight = getImageHeight();
            translateMatrixAfterRotate(Matrix.MTRANS_Y, transY, prevActualHeight, actualHeight, prevViewHeight, viewHeight, drawableHeight);

            //
            // Set the matrix to the adjusted scale and translate values.
            //
            matrix.setValues(m);
        }
        fixTrans();
        setImageMatrix(matrix);
    }
If the normalizedScale is equal to 1, then the image is made to fit the screen. Otherwise,
it is made to fit the screen according to the dimensions of the previous image matrix. This
allows the image to maintain its zoom after rotation.
app/src/main/java/home/smart/fly/animations/customview/gallery/TouchImageView.java