CClientDC and DC not Drawing on ChtmlEditCtrl - c++

Question

Hi all I am working with a CHtmlEditCtrl in MFC. I want to draw some random rectangles and lines inside a function handling right click event.
The ChtmlEditCtrl control is created from static using this snippet:
bool CHtmlEditCtrlEx::CreateFromStatic( UINT nID, CWnd* pParent ) {
CStatic wndStatic;
if ( !wndStatic.SubclassDlgItem(nID, pParent)) {
return false;
}
CRect rc;
wndStatic.GetWindowRect( &rc );
pParent->ScreenToClient( &rc );
if (Create( 0, (WS_CHILD | WS_VISIBLE), rc, pParent, nID, 0 )) {
...
}
Then I override the CWnd::pretranslate() function as thus:
CClientDC dcc(this);
switch (pMsg->message) {
case WM_RBUTTONUP: // Right-click
// Just some dummy values
DrawSquigly(dcc, 600, 240, 20);
break;
}
the DrawSquigly() function is defined as thus:
void CHtmlEditCtrlEx::DrawSquigly(CDC &dcc, int iLeftX, int iWidth, int iY)
{
CAMTrace trace;
trace.Trace("Drawing Squiggly");
//dcc.TextOut(10, 10, CString(_T("I used a client DC!")));
CPen * oldPen;
CBrush * oldBrush;
oldPen = (CPen *) dc.SelectStockObject(WHITE_PEN);
dcc.MoveTo(5,10);
dcc.LineTo(80, 10);
dcc.SelectObject(oldPen);
//GDI 002_2: Create custom pen with different Line thickness.
CPen thick_pen(PS_SOLID, 3, RGB(0,255,0));
oldPen = dc.SelectObject(&thick_pen);
dcc.MoveTo(5, 20);
dcc.LineTo(80,20);
dcc.SelectObject(oldPen);
//GDI 002_3: Create a Rectangle now
dcc.Draw3dRect(5,30,80,70, RGB(25,25,255), RGB(120,120,120));
//GDI 002_4: Create a Brush that we can use for filling the
// closed surfaces
CBrush brush(RGB(255,0,255));
oldBrush = dc.SelectObject(&brush);
dcc.Rectangle(5,110,80,140);
dcc.SelectObject(oldBrush);
//GDI 002_5: Hatch Brush is useful to apply a pattern in stead
//of solid fill color
CBrush* hatBrush = new CBrush();
hatBrush->CreateHatchBrush(HS_CROSS, RGB(255,0,255));
oldBrush = dc.SelectObject(hatBrush);
dcc.FillRect(new CRect(5,160,80,190), hatBrush);
dcc.SelectObject(oldBrush);
}
but no drawing happens when I right click. I think I am missing something especially because I am new to MFC.
I have added a trace to the top of the event handler to be sure that the function is getting called and it is.
Can anyone please point me the right direction?

Answer 1

There are actually 2 device context in your code: one you pass as parameter in the call (we don't know where it comes from) and the other created locally in the drawing function.
Normally, when the systems gives you a DC it expects you draw something in it, not that you draw into something else.
If the window you are working on is layered, the system gives you a memory context you draw in that is - upon clearing - blit-ted onto the window itself with some window manager effect.
My suspect is that -by allocating a second dc- your drawing are ovewritten when the first one (you left blank) is cleared upon returning from the message handler.