Routines (alphabetical) > Object Classes > Graphics Object Classes > IDLgrWindow::OnWheel

# IDLgrWindow::OnWheel

The IDLgrWindow::OnWheel procedure method handles notification (from the native window device) that a mouse wheel event has occurred.

Note: This method is only useful in conjunction with the Export Bridge. The method is only a stub and provides no functionality. In your subclass of IDLgrWindow, you should override this method to provide your own functionality. Your method will be automatically called by the Export Bridge. For more information, see "Exporting Drawable Objects"(Chapter 11, IDL Connectivity Bridges in the `help/pdf` directory of your IDL installation).

## Syntax

Obj->[IDLgrWindow::]OnWheel, X, Y, Delta, Modifiers

## Arguments

### X

A long integer representing the x-location (in device coordinates) of the mouse event.

### Y

A long integer representing the y-location (in device coordinates) of the mouse event.

### Delta

A long integer giving the direction and distance that the wheel was rolled. Pushing the wheel generates positive values, pulling the wheel generates negative values. The magnitude of the value depends on the device setting for the individual mouse, but is usually limited to small integer values such as +1, -1, +2, -2, etc.

### Modifiers

A long integer containing a bitwise mask indicating which modifier keys are active at the time of the wheel event. If a bit is zero, the key is up; if the bit is set, the key is pressed. The following table describes the bits in this bit mask:

Bit | Value | Modifier Key
0 | 1 | Shift
1 | 2 | Control
2 | 4 | Caps Lock
3 | 8 | Alt

## Keywords

None

## Version History

6.4 | Introduced