如何在 Mfc C++ 中创建透明矩形？

Question

I want to create a rectangle total transparent i try this code. Any idea how to do that?

 BOOL CHtmlDlgTestDlg::PreTranslateMessage(MSG* pMsg)
    {

        if (pMsg->message == WM_MOUSEMOVE && (pMsg->wParam & MK_LBUTTON))
        {
            CPoint p = pMsg->pt;
            ScreenToClient(&p);
            CRect r(10, 15, 380, 50);
            CDC* pCDC = GetDC();
            pCDC->Rectangle(r);
            CBrush brush;


            brush.CreateSolidBrush(RGB(255, 255, 0));
            pCDC->FillRect(&r, &brush);



            if (r.PtInRect(p))
            {
                ReleaseCapture();
                SendMessage(WM_NCLBUTTONDOWN, HTCAPTION, 0);
                SendMessage(WM_NCLBUTTONUP, HTCAPTION, 0);
                return 1;
            }

        }
        return CDHtmlDialog::PreTranslateMessage(pMsg);
    }

This is mfc c++ code example.

Answer 1

First: How the hell do you want to create a transparent rectangle, if you created a solid brush and after did a FillRect with it?

If you wanted to do that using a brush, you would have to go with one "that not paints anything" like:

brush.CreateStockObject(NULL_BRUSH);

May be you wanted a rectangle with an opaque border and transparent interior. In that case, in addition to the null brush, the object you need to create is a CPen.

CPen p(PS_SOLID, 0, RGB(255, 255, 0));
pCDC->SelectObject(&p);
pCDC->Rectangle(r);

Secondly, I think the DrawEdge function is the simplest way to go if you dont' care about the border color (the colors are fixed; search DrawEdge in Google images to see what I mean).