If Flags contains MouseFlags.Wheel, then mouseData specifies the amount of wheel movement. 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. One wheel click is defined as WHEEL_DELTA, which is 120. Windows Vista: If dwFlags contains MouseFlags.HWheel, then dwData specifies the amount of wheel movement. A positive value indicates that the wheel was rotated to the right; a negative value indicates that the wheel was rotated to the left. One wheel click is defined as WHEEL_DELTA, which is 120. If dwFlags does not contain MouseFlags.Wheel, MouseFlags.XDown, or MouseFlags.XUp, then mouseData should be zero. If dwFlags contains MouseFlags.XDown or MouseFlags.XUp, then mouseData specifies which X buttons were pressed or released. This value may be any combination of the following flags. XBUTTON1 = 0x1 XBUTTON2 = 0x2