In meiner Hilfe zu WM_MOUSEWHEEL steht:
Zitat:
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
...
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.