@Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
            if (isRotationEnabled) {
                // Set the pie rotation directly.
                final RectF circleOval = pieChart.getCircleOval();
                final float centerX = circleOval.centerX();
                final float centerY = circleOval.centerY();
                float scrollTheta = vectorToScalarScroll(distanceX, distanceY, e2.getX() - centerX, e2.getY() -
                        centerY);
                pieChart.setChartRotation(pieChart.getChartRotation() - (int) scrollTheta / FLING_VELOCITY_DOWNSCALE,
                        false);
                return true;
            }

            return false;
        }
Reference to PieChartView to use some methods specific for that kind of chart.
hellocharts-library/src/lecho/lib/hellocharts/gesture/PieChartTouchHandler.java