MFC how to save and reuse the current device context CDC - c++

Question

Well simply what I need to do is to create a grid of rectangle and fill any selected case of that grid at the user click. thus I save the parameters (color, position..). The problem is when I try to fill the case at the click event I can't any changes maybe because the device context is changed even if I use GetDC() method. So is there any way to save the current created on OnDraw() method for exmaple and use it somewhere in another function, I tried to use SaveDC() and RestoreDC() but in vain.
Here's some of my code:
void CXThiefManView::OnDraw(CDC* pDC)
{
CXThiefManDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
if (!pDoc)
return;
CRect rcClient;
GetClientRect(&rcClient);
// Get the background color of the board
COLORREF clr = pDoc->GetBoardSpace(-1, -1);
// Draw the background first
pDC->FillSolidRect(&rcClient, clr);
// Create the brush for drawing
CBrush br;
br.CreateStockObject(HOLLOW_BRUSH);
CBrush* pbrOld = pDC->SelectObject(&br);
// Draw the squares
for (int row = 0; row < pDoc->GetRows(); row++)
{
for (int col = 0; col < pDoc->GetColumns(); col++)
{
// Get the color for this board space
clr = pDoc->GetBoardSpace(row, col);
// Calculate the size and position of this space
CRect rcBlock;
rcBlock.top = row * pDoc->GetHeight();
rcBlock.left = col * pDoc->GetWidth();
rcBlock.right = rcBlock.left + pDoc->GetWidth();
rcBlock.bottom = rcBlock.top + pDoc->GetHeight();
// Fill in the block with the correct color
pDC->FillSolidRect(&rcBlock, clr);
// Draw the block outline
pDC->Rectangle(&rcBlock);
}
}
saveState = pDC->SaveDC();
DrawItem(pDC, pDoc->GetThiefRow(), pDoc->GetThiefCol(), pDoc->GetThiefColor());
}
void CXThiefManView::OnLButtonDown(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
CView::OnLButtonDown(nFlags, point);
CXThiefManDoc* pDoc = GetDocument();
// the draw item here to fill the case
DrawItem(GetDC(), 5, 5, RGB(0, 0, 0));
}

Answer 1

Underneath all those MFC function, the WINAPI functions of the same name are being called. In WINAPI, GetDC returns a new device context. SaveDC & RestoreDC allow you to save and restore the state (brush, font etc...) of a specific DC handle, but that doesn't cross to other handles.
There's nothing MFC can do about it, nor can you. You have to reconfigure the new DC handle for your needs.

Answer 2

Handle from GetDC has to be released by ReleaseDC. Please see GetDC
Or use CClientDC dc(this) which has automatic cleanup, it's usage is similar, for example Draw(&dc,...);.
As to your main question, you can save the drawing on a bitmap. The bitmap can be saved.
define:
CBitmap m_bitmap;
CDC m_memdc;
initialize the bitmap and dc:
CClientDC dc(this);
m_bitmap.CreateCompatibleBitmap(&dc, 2000, 1200);
//this creates a bitmap as big as the screen...
m_memdc.CreateCompatibleDC(&dc);
m_memdc.SelectObject(m_bitmap);
m_memdc.FillSolidRect(0, 0, 2000, 1200, RGB(255, 255, 255));
//draw on m_memdc, then draw memdc on to dc
Usage:
void CMyWindow::OnPaint()
{
CWnd::OnPaint();
CClientDC dc(this);
CRect rc;
GetClientRect(&rc);
dc.BitBlt(0, 0, rc.Width(), rc.Height(), &m_memdc, 0, 0, SRCCOPY);
}
void CMyWindow::OnMouseMove(UINT k, CPoint p)
{
CClientDC dc(this);
CRect rc;
GetClientRect(&rc);
if (k & MK_LBUTTON)
{
//draw on m_memdc, (instead of drawing on dc)
m_memdc.SetPixel(p.x, p.y, RGB(0,0,0));
m_memdc.SetPixel(p.x, p.y+1, RGB(0,0,255));
//when finished drawing, draw m_memdc on to dc
dc.BitBlt(0, 0, rc.Width(), rc.Height(), &m_memdc, 0, 0, SRCCOPY);
}
}