Texas Instruments TI89 Developer Guide - Page 235

Chapter 17: Graphing 193 17.4. gr_active and gr_other can point to either. An app should also be aware that a user can change graph modes or even change to one graph mode while the app is open, which may cause the app to suddenly start referencing the other graph. If any MODE settings are changed while the app is open, a CM_MODE_CHANGE event message will be sent to the app (see section 8.1. Mode Settings). An ASM can change which window is active, allowing it to choose Graph 1 or Graph 2 if desired. When the calculator is returned to one graph mode, the graph that is kept as the current graph will be the one corresponding to the active split screen at that time. If the top or left split is the active window, Graph 1 will be the current active graph. If the bottom or right split is the active window, Graph 2 will be the current graph. The data for the graph that is not current is not lost, however. If the graphs were different modes, selecting the mode of the other graph will restore that graph as the current active graph. If both graphs were the same mode, all the data is saved but can only be viewed again by going back into two graph mode and setting both graphs to the same mode again. The graph formats and window settings for the second graph will be the same ones that were there before. Since the functions are shared, they will contain the current definitions. If the previous definitions are desired, a graph database should be created before leaving two graph mode. Graphing Functions Each variable in the symbol table has two graph reference flags, one for the graph associated with gr_active and the other for the graph associated with gr_other. Before starting a graph, the gr_active graph reference flags and graph backup screen are cleared and the graph in progress flag is set (gr_flags.gr_in_progress). While the graph in progress flag is set, the graph reference flag for every variable accessed will be set. The graph in progress flag is reset when the graph is stopped for any reason, whether it is complete or not. The dirty flag (gr_active->gr_win_flags & GR_DIRTY) is used to tell the system that the graph must be regraphed the next time it is displayed. It is set if the graph is interrupted for any reason, leaving an incomplete graph on the screen, so the next time the graph screen is displayed another regraph will occur. When the graph is complete and error-free, the dirty flag is reset. These flags are the basis for the Smart Graph feature. Any time a variable is changed, the graph reference flags are checked. If either is set, the dirty flag for the appropriate graph (gr_active or gr_other or both) will be set, triggering a regraph the next time that graph is displayed. Many other things can also cause the dirty flag to be set, such as selecting a new split setting, changing the angle mode, changing any of the Window variables, changing a selected graph system function, etc. Selecting an additional graph function or defining a new graph function (which automatically selects it for graphing), does not set the dirty flag. When a new function is added to the graph, the dirty flag and graph in progress flags operate TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001