code: public void drawInBackground(Canvas canvas) {
          Axis axis = chart.getChartData().getAxisYLeft();
          if (null != axis) {
              prepareAxisToDraw(axis, LEFT);
              drawAxisLines(canvas, axis, LEFT);
          }
  
          axis = chart.getChartData().getAxisYRight();
          if (null != axis) {
              prepareAxisToDraw(axis, RIGHT);
              drawAxisLines(canvas, axis, RIGHT);
          }
  
          axis = chart.getChartData().getAxisXBottom();
          if (null != axis) {
              prepareAxisToDraw(axis, BOTTOM);
              drawAxisLines(canvas, axis, BOTTOM);
          }
  
          axis = chart.getChartData().getAxisXTop();
          if (null != axis) {
              prepareAxisToDraw(axis, TOP);
              drawAxisLines(canvas, axis, TOP);
          }
      }
docs: Prepare axes coordinates and draw axes lines(if enabled) in the background.
  
  @param canvas