GameViewportClient中有个变量控制是否显示硬件鼠标：
var transient bool bDisplayHardwareMouseCursor
也就是系统的光标，一般通过该类中的函数来操纵：
simulated event SetHardwareMouseCursorVisibility(bool bIsVisible) { local Vector2D ViewportSize; //If we are going to be turning on the hardware cursor when it was not already on, we will move the cursor to the middle of the screen if (bIsVisible && !bDisplayHardwareMouseCursor) { GetViewportSize(ViewportSize); SetMouse(ViewportSize.X/2,ViewportSize.Y/2); } bDisplayHardwareMouseCursor = bIsVisible; ForceUpdateMouseCursor(TRUE); }
其中ForceUpdateMouseCursor是native函数，调用到UGameViewportClient::ForceUpdateMouseCursor，
在Windows上的实现类为FWindowsViewport，其成员函数
void FWindowsViewport::UpdateMouseLock( UBOOL bEnforceMouseLockRequestedFlag )
在每个tick中被调用，会对该控制变量进行检测：
RECT ClipRect; UBOOL bIsHardwareCursorVisible = (GEngine && GEngine->GameViewport && GEngine->GameViewport->bDisplayHardwareMouseCursor); UBOOL bIsAnyCursorVisible = bIsSystemCursorVisible || bIsHardwareCursorVisible; UBOOL bClipRectValid = (::GetClipCursor( &ClipRect ) != 0); UBOOL bHasFocus = HasFocus(); UBOOL bShouldMouseLock = bEnforceMouseLockRequestedFlag ? bMouseLockRequested : bHasFocus && (IsFullscreen() || !bIsAnyCursorVisible || bMouseLockRequested);
最后在bShouldMouseLock为TRUE时，调用::ClipCursor锁定鼠标。
原文：http://www.cnblogs.com/wellbye/p/5330020.html