Two Graph Mode - Texas Instruments TI-89 Developer's Manual

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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
Chapter 17: Graphing
Beta Version January 26, 2001