WHEEL_CB
Action generated when the mouse wheel is rotated. If this callback is not defined, the wheel will automatically scroll the canvas in the vertical direction by some lines, the SCROLL_CB callback if defined will be called with the IUP_SBDRAGV operation.
Callback
int function(Ihandle *ih, float delta, int x, int y, char *status);ih: identifier of the element that activated the
event.
delta: the amount the wheel was rotated in
notches.
x, y: position in the canvas where the
event has occurred, in pixels.
status: status of mouse buttons and certain keyboard
keys at the moment the event was generated. The same macros used for BUTTON_CB can be used for this
status.
Notes
In GTK, GTK 4, Motif, FLTK, EFL and Haiku, delta is always 1 or -1. In Windows, WinUI and Qt, delta is normalized in WHEEL_DELTA units (1 per notch typical, 2 or more on some devices). In macOS and iOS, delta can be fractional (precision or trackpad scrolling reports sub-notch values).