Texas Instruments TI89 Developer Guide - Page 631
GR_WIN_VARS, Computes Window variable
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Appendix A: System Routines - Graphing 589 CptDeltay Declaration: BYTE CptDeltay (GR_WIN_VARS * ptr) Category(ies): Graphing Description: Computes Window variable ∆y using the viewing window values and window height in the GR_WIN_VARS struct pointed to by ptr and sets the GR_DIRTY flag (ptr ->gr_win_flags & GR_DIRTY) if the newly computed ∆y is not equal to the old ∆y. Inputs: ptr - Pointer to the GR_WIN_VARS struct to use for viewing window values and window height (gr_active for the active graph window, gr_other for the second graph in two graph mode). Outputs: Returns 0 if ∆y could not be computed due to invalid viewing window values, otherwise returns 1. If valid, the new ∆y is stored in (ptr ->rngp)[GR_DELTAY]. Assumptions: Assumes the window height in ptr ->ymaxpix is correct. If the window size has been changed since the graph was last displayed, ptr ->ymaxpix will not have been updated, so the new ∆y will not be correct. In this case, ∆y will automatically be recomputed the next time the graph is displayed, using the correct window height. Side Effects: If the GR_DIRTY flag is set, the graph will be redrawn next time it is displayed. Availability: All versions of the TI-89 / TI-92 Plus. TI-89 / TI-92 Plus Differences: None See Also: CptDeltax Example: /* make sure deltax and deltay are correct */ if(gr_active->gr_win_flags & GR_DIRTY) /* viewing window values may have changed, recompute deltax and deltay */ if ( ! ( CptDeltax(gr_active) && CptDeltay(gr_active) ) ) ER_throw( ER_RANGE ); /* cannot compute valid deltax and deltay */ TI-89 / TI-92 Plus Developer Guide Not for Distribution Beta Version January 26, 2001
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