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4/8/2010

This message is posted to the window that has the focus when the user presses the mouse wheel. The DefWindowProcfunction propagates the message to the parent window of the window that has focus. You should not forward the message internally because DefWindowProcpropagates the message up the chain of parent windows until DefWindowProcfinds a window that processes the message.

A window receives this message through the WindowProcfunction for the window.

Syntax 

WM_MOUSEWHEEL 

fwKeys = LOWORD(
wParam); 

zDelta = HIWORD(
wParam);

xPos = LOWORD(
lParam); 

yPos = HIWORD(
lParam);

Parameters

fwKeys

Indicates the mouse buttons and keys that the user pressed. The following table shows the possible values, which can be combined.

Value Description

MK_CONTROL

The user pressed the CTRL key.

MK_LBUTTON

The user pressed the left mouse button.

MK_MBUTTON

The user pressed the middle mouse button.

MK_RBUTTON

The user pressed the right mouse button.

MK_SHIFT

The user pressed the SHIFT key.
zDelta

Indicates that the mouse wheel was pressed, expressed in multiples or divisions of WHEEL_DELTA, which is 120.

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.

Return Value

An application that processes this message should return zero.

Remarks

None.

Requirements

Header windows.h
Library coredll.lib
Windows Embedded CE Windows CE .NET 4.0 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also