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Overview |
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Group |
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Quick Info
Windows NT
| Yes
| Win95
| No
| Win32s
| No
| Import Library
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| Header File
| winuser.h
| Unicode
| WinNT
| Platform Notes
| None
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WM_MOUSEWHEEL
[New - Windows NT]
The WM_MOUSEWHEEL message is sent to the focus window when the mouse wheel is
rotated. The DefWindowProc function propagates the message to the window's
parent. There should be no internal forwarding of the message, since DefWindowProc
propagates it up the parent chain until it finds a window that processes it.
WM_MOUSEWHEEL
fwKeys = LOWORD(wParam); // key flags
zDelta = (short) HIWORD(wParam); // wheel rotation
xPos = (short) LOWORD(lParam); // horizontal position of pointer
yPos = (short) HIWORD(lParam); // vertical position of pointer
Parameters
fwKeys
Value of the low-order word of wParam. Indicates whether various virtual keys are down. This parameter can be any
combination of the following values:
Value
| Description
| MK_CONTROL
| Set if the CTRL key is down.
| MK_LBUTTON
| Set if the left mouse button is down.
| MK_MBUTTON
| Set if the middle mouse button is down.
| MK_RBUTTON
| Set if the right mouse button is down.
| MK_SHIFT
| Set if the SHIFT key is down.
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zDelta
The value of the high-order word of wParam. Indicates the distance that the wheel is rotated, expressed in multiples or
divisions of WHEEL_DELTA, which is 120. A positive value indicates that the
wheel was rotated forward, away from the user; a negative value indicates that the
wheel was rotated backward, toward the user.
xPos
Value of the low-order word of lParam. Specifies the x-coordinate of the pointer, relative to the upper-left corner
of the screen.
yPos
Value of the high-order word of lParam. Specifies the y-coordinate of the pointer, relative to the upper-left corner
of the screen.
Remarks
The zDelta parameter will be a multiple of WHEEL_DELTA, which is set at 120.
This is the threshold for action to be taken, and one such action (for example,
scrolling one increment) should occur for each delta.
The delta was set to 120 to allow Microsoft or other vendors to build
finer-resolution wheels in the future, including perhaps a freely-rotating wheel with
no notches. The expectation is that such a device would send more messages per
rotation, but with a smaller value in each message. To support this possibility,
you should either add the incoming delta values until WHEEL_DELTA is reached
(so for a given delta-rotation you get the same response), or scroll partial
lines in response to the more frequent messages. You could also choose your scroll
granularity and accumulate deltas until it is reached.
See Also
GetSystemMetrics, mouse_event, SystemParametersInfo
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