Texas Instruments TI89 Developer Guide - Page 234
Two Graph Mode, System apps and routines, including
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192 Chapter 17: Graphing 17.3. Two Graph Mode If the app or ASM may be executing when the calculator is in two graph mode and needs to interact with the Graph application, graphing system variables or graph system functions, or any graph related application (Window Editor, Y= Editor, or Table), it must be aware of how two graph mode works. In two graph mode (split screen selected and Number of Graphs = 2 on the MODE screen) two independent graphs can be shown at the same time. The graph mode for each is set separately. Other settings on the MODE screen are global and apply to both graphs, such as Current Folder, Angle mode and Complex Format. Stat plot definitions and graph functions are also global although different functions and stat plots can be selected for each graph. In two graph mode, any graph related application or reference to graphing system variables or graph system functions always refers to the graph corresponding to the active split screen window. In the top or left split (AP_SIDE_A), this will always be Graph 1. Graph 2 is always in the bottom or right split (AP_SIDE_B). A calculator user keeps track of this visually, with the active graph number and its mode both shown in the status line which gets updated as the user switches from one window to the other. Graph 1 and Graph 2 can both be different graph modes or they can have the same mode. When they have the same mode, the function definitions and styles are shared (if the Y= Editor is displayed in both windows, they show the same function definitions), but different functions can be selected to be plotted in each screen. The Smart Graph feature still applies to each graph individually as much as possible so changing a function that is only graphed on one screen does not cause the other screen to also regraph. The Window variables, graph format settings, and table editors are completely independent for each graph, even when both have the same graph mode. If a graph is in one window and a table is in the other, one is using Graph 1 data and the other is using Graph 2 data. Two applications generated from the same set of graph data cannot be shown at the same time in two graph mode. System apps and routines, including VarStore, access all graph related data through the global variables gr_active and gr_other. gr_active is a pointer to a GR_WIN_VARS struct containing all the information for the active graph. gr_other points to the information for the second graph in two graph mode. As the calculator user switches between the two windows in two graph mode, the pointers in gr_active and gr_other are swapped so that gr_active is always referring to the active graph. An app or ASM will be referencing graph related data that corresponds to whichever window is active when the app or ASM is executing. This means that the first time your app is opened, gr_active may be referring to Graph 1, and if it is opened again, it may be referring to Graph 2, depending on which window the app happens to be opened in. Although the user refers to Graph 1 and Graph 2 to distinguish between the two graphs, internally an app or ASM is usually not aware whether it is working with Graph 1 or 2 since TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001
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