Cptdeltay - Texas Instruments TI-89 Developer's Manual

Appendix A: System Routines — Graphing

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 (
Inputs: ptr — Pointer to the GR_WIN_VARS struct to use for viewing window
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
has been changed since the graph was last displayed,
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 );
TI-89 / TI-92 Plus Developer Guide
ptr ->gr_win_flags & GR_DIRTY
y is not equal to the old y.
values and window height (gr_active for the active graph window,
gr_other for the second graph in two graph mode).
/* cannot compute valid deltax and deltay */
Not for Distribution
.
is correct. If the window size
ptr ->ymaxpix
589
) if the newly computed
will
ptr ->ymaxpix
Beta Version January 26, 2001