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鼠标消息的位置获取正确方式

Posted on 2016-10-10 11:32  sgao  阅读(1059)  评论(0编辑  收藏

今天碰到一个问题,就是在多屏的时候,WM_NCHITTEST结果不正确,经检查发现在多屏的情况下,鼠标的位置是有可能出现负值的,但是如果还是用LoWord(Msg.LParam)和HiWORD(Msg.LParam)取鼠标的位置,就会取出不正确的值,因为这两个函数只会返回正值。

查询MSDN的WM_NCHITTEST有下面一段话。

Remarks

Use the following code to obtain the horizontal and vertical position:

 
 
xPos = GET_X_LPARAM(lParam); 
yPos = GET_Y_LPARAM(lParam);


As noted above, the x-coordinate is in the low-order short of the return value; the y-coordinate is in the high-order short (both represent signed values because they can take negative values on systems with multiple monitors). If the return value is assigned to a variable, you can use the MAKEPOINTS macro to obtain a POINTS structure from the return value. You can also use the GET_X_LPARAM or GET_Y_LPARAM macro to extract the x- or y-coordinate.

Important  Do not use the LOWORD or HIWORD macros to extract the x- and y- coordinates of the cursor position because these macros return incorrect results on systems with multiple monitors. Systems with multiple monitors can have negative x- and y- coordinates, and LOWORD and HIWORD treat the coordinates as unsigned quantities.
 
在delphi中可通过下面代码获取正确的鼠标位置:
 
LMousePt.X := SmallInt(Msg.LParamLo);
LMousePt.Y := SmallInt(Msg.LParamHi);

//或者

LMousePt.X := SmallInt(Msg.LParam);
LMousePt.Y := (SmallInt)HiWord(Msg.LParam);