@Override
        public boolean onScale(ScaleGestureDetector detector) {
            if (isZoomEnabled) {
                float scale = detector.getCurrentSpan() / detector.getPreviousSpan();
                if (Float.isInfinite(scale)) {
                    scale = 1;
                }
                return chartZoomer.scale(computator, detector.getFocusX(), detector.getFocusY(), scale);
            }

            return false;
        }
Touch Handler for preview charts. It scroll and zoom only preview area, not all preview chart data.
hellocharts-library/src/lecho/lib/hellocharts/gesture/PreviewChartTouchHandler.java