在上下文之间传输对象的问题

Question

I try to make some easy application which scrolling ECG singal which is drawing on bitmap grid. Environment which I use is Visual Studio 2013 with C++ MFC. My problem is with transfer gdi object like LineTo or Rectangle() function from dcMemory to my main device context (cdc). Before I make similar application using WinAPI and all go well. I spent a lot time with studying msdn and looking answer with google, and I have no idea why only bitmap from Bitmap.LoadBitmapW(IDB_BITMAP2) is printing. Can anybody help me?

Message when button from menu was calling:

 void CToradex_MFC_BitmapView::OnBitmapDraw()
    {
        Bitmap.LoadBitmapW(IDB_BITMAP2);
        cdc.CreateDC(L"DISPLAY", NULL, NULL, NULL);
        dcMemory.CreateCompatibleDC(&cdc);
        LoadData();
        GetObject(Bitmap, sizeof(bmpInfo), &bmpInfo);
        dcMemory.SelectObject(&Pen);
        dcMemory.Rectangle(100, 100, 200, 200);
        dcMemory.LineTo(100, 300);
        dcMemory.SelectObject(&Bitmap);
        druk.DrawECG(&dcMemory, pointer, 3, SIGN_LEN);
    
    }

---

Message on mouse button down:

void CToradex_MFC_BitmapView::OnLButtonDown(UINT,CPoint)
{   

    CToradex_MFC_BitmapDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    POINT p;
    GetCursorPos(&p);
    x_start = p.x;
    y_start = p.y;
}

---

Message on mouse move:

void CToradex_MFC_BitmapView::OnMouseMove(UINT, CPoint)
{   
POINT d;

//CDC * pDC = this->GetDC();
//this->GetClientRect(&rect);
//rect = CRect(rect.left, rect.top, rect.right, rect.bottom);
if (GetCursorPos(&d))
{
    move_x = d.x - x_start;
    move_y = d.y - y_start;
    cdc.BitBlt(move_x, move_y, bmpInfo.bmWidth, bmpInfo.bmHeight, &dcMemory, 0, 0, SRCCOPY);
    x_start = d.x;
    y_start = d.y;
//Invalidate();
Sleep(10);
}

Below link for all.cpp file:

https://pastebin.com/h7hcLJbz

Answer 1

You need to select a bitmap into your DC first, then draw on top of it:

dcMemory.SelectObject(&Bitmap);
dcMemory.SelectObject(&Pen);
dcMemory.Rectangle(100, 100, 200, 200);
dcMemory.LineTo(100, 300);
druk.DrawECG(&dcMemory, pointer, 3, SIGN_LEN);