WM_MOUSEWHEEL (Compact 2013)

3/28/2014

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

A window receives this message through the WindowProc function 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

See Also

Reference

Mouse Messages
DefWindowProc
GetSystemMetrics
mouse_event
SystemParametersInfo
WindowProc