Friday, March 18, 2011

How to Add a Graph Cursor

In this post we explain how to add, present and use a graph cursor.

The goal of adding a graph cursor is to find the exact values of a point along the plotted graph, the next example contains a graph of a simple parabolic curve, clicking anywhere on the graph will snap to the nearest point on the graph and show the values on the designated numeric controls.

To add a graph cursor you need to do the following 2 steps :

1. Adding the Graph Cursor

  • At the .uir tab of the workspace edit the graph control and click the Cursors button.
  • Change the number of cursors to 1 and the mode to "Snap to Point".

2. Showing the Graph Cursor Values

  • At the edit graph window enter a callback function ("graphFunc") and click OK to exit and save changes.
  • Generate the callback function.
  • Go to the .c tab at the workspace and locate the callback function.
  • Define 2 double variables in order to store the graph cursor values.:
double x,y;
  • Assign the graph cursor values to the variables:
GetGraphCursor (panelHandle, PANEL_GRAPH, 1, &x, &y);
  • Assign the variables values to a numeric controls:
SetCtrlVal (panelHandle, PANEL_NUMERIC_X, x);
SetCtrlVal (panelHandle, PANEL_NUMERIC_Y, y);