MFC: Move a rectangle on client area - mfc

Question

I want to create an MFC application that move an rectangle in the client area by hold left mouse and move to new position. But the rectangle move too fast although I move the mouse slowly.
My code here:
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.
}
I am new in MFC. Can someone help me please ? Thank everyone.

Answer 1

The Problem is that you always add the total Change again to the current Position.
(point.x - oPoint.x) is the complete horizontal change.
But lpStart contains always the current rectangle coords.
Save the rectangle coords of lpStart also as a oRect when the button is clieked.
CRect newRect = oRect;
newRect.OffsetRect(point.x - oPoint.x, point.y - oPoint.y);
lpStart = newRect;
Invalidate();
Or set oPoint to Point after you moved the rectangle. with tis trick you always track only the relative changes.
...your code
// Save the new oPoint to makle the movements relative
oPoint = Point;
Invalidate();