MFC：在客户区域移动一个矩形

Question

我想创建一个MFC应用程序，通过按住鼠标左键并移动到新位置来移动客户区域中的矩形。但是，尽管我慢慢移动鼠标，矩形移动得太​​快。 我的代码在这里：

class CEmpWnd : public CFrameWnd 
{ 
protected: 
    POINT lpStart, rpStart, oPoint; 
    bool clicked; 
public: 
    CEmpWnd(void); 
    virtual ~CEmpWnd(void); 
    afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct); 
    afx_msg void OnPaint(); 
    afx_msg void OnLButtonDown(UINT nFlags, CPoint point); 
    afx_msg void OnLButtonUp(UINT nFlags, CPoint point); 
    afx_msg void OnMouseMove(UINT nFlags, CPoint point); 
    DECLARE_MESSAGE_MAP() 
}; 


int CEmpWnd::OnCreate(LPCREATESTRUCT lpCreateStruct) 
{ 
    lpStart.x = 0; 
    lpStart.y = 0; 
    rpStart.x = 100; 
    rpStart.y = 100; 
    clicked = false; 
    if (CWnd::OnCreate(lpCreateStruct) == -1) 
     return -1; 
    SetTimer(ID_TIMER, 250, NULL); 
    SetWindowText(L"Phùng Khánh Hiên "); 
    return 0; 
} 

void CEmpWnd::OnPaint() 
{ 
    CPaintDC dc(this); // device context for painting 
    Rectangle(dc, lpStart.x, lpStart.y, rpStart.x, rpStart.y);  //Draw a rectangle 
} 

void CEmpWnd::OnLButtonDown(UINT nFlags, CPoint point) 
{ 
    if(point.x >= lpStart.x && point.x <= rpStart.x && point.y >= lpStart.y && point.y <= rpStart.y)  //If click on rectangle area 
    { 
     clicked = true; 
     oPoint = point; 
    } 
} 

void CEmpWnd::OnMouseMove(UINT nFlags, CPoint point) 
{ 
    if(clicked == true) 
    { 
     lpStart.x += (point.x - oPoint.x);    //Increase left-top and right-bot Points 
     rpStart.x += (point.x - oPoint.x);   
     lpStart.y += (point.y - oPoint.y); 
     rpStart.y += (point.y - oPoint.y); 
     lpStart.x = max(0, lpStart.x);     //Keep current size of rectangle. 
     lpStart.y = max(0, lpStart.y); 
     rpStart.x = max(100, rpStart.x); 
     rpStart.y = max(100, rpStart.y); 
     Invalidate();         //Eraze old Rectangle and redraw new one. 
    } 
} 

void CEmpWnd::OnLButtonUp(UINT nFlags, CPoint point) 
{ 
    clicked = false;         //Release drawing. 
} 

我是新的MFC。有人能帮助我吗 ？谢谢大家。

Answer 1

问题是您总是将总变化量再次添加到当前位置。

（point.x - oPoint.x）是完整的水平变化。 但lpStart始终包含当前的矩形坐标。 当按钮被关闭时，将lpStart的矩形坐标也保存为一个oRect。

CRect newRect = oRect; 
newRect.OffsetRect(point.x - oPoint.x, point.y - oPoint.y); 
lpStart = newRect; 
Invalidate(); 

或者在移动矩形后设置oPoint to Point。你总是跟踪相对变化。

...your code 
// Save the new oPoint to makle the movements relative 
oPoint = Point; 
Invalidate();