A C chart chart generated and painting application example, the control program of the resulting PNG format chart image file, the example will demonstrate to initialize the chart of general properties, initialization and static display coordinates, x, y axis, data points for: (0, 0), (500, 0), (1000, 0)...(3500, 0) of its index is 0 to 7 points, determine the current value of the scroll bar in which range, and get the upper and lower range, determine the direction of the drag of the scroll bar, depending on the value of the scroll bar to update the x axis coordinates, to write content to create a PNG file.