Cclientdc and dc not drawing on chtmleditctrl

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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.

What I have tried:

The ChtmlEditCtrl control is created from static using this snippet:

C++

    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?

Posted 3-Mar-16 23:49pm

Ashiru Ali

Updated 22-Mar-16 1:17am

Richard MacCutchan

v2

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Comments

Richard MacCutchan 4-Mar-16 5:59am

I think you are doing things in the wrong place. All drawing in Windows should be done in response to a WM_PAINT message. If you draw on a control anywhere else then whatever you render is likely to be erased as soon as the control (Window) receives the next WM_PAINT message. I am not sure why you chose this particular control but maybe you should just use a basic Window.

Ashiru Ali 7-Mar-16 4:50am

Hi, According to MSDN "The system sends an internal WM_PAINT message only once. After an internal WM_PAINT message is returned from GetMessage or PeekMessage or is sent to a window by UpdateWindow, the system does not post or send further WM_PAINT messages until the window is invalidated or until RedrawWindow is called again with the RDW_INTERNALPAINT flag set." in my understanding to get a DC for this message, the CPaintDC is more appropriate. it happens only once (The window is drawn or specifically redrawn)

Richard MacCutchan 7-Mar-16 6:53am

Well if it works for you that is fine.

Arthur V. Ratz 21-Mar-16 2:31am

5.

[no name] 9-Mar-16 16:16pm

At some point, Windows will send a WM_PAINT to the control. It will erase any drawing done by your pre-translate code above.

A more ideal approach would be to have the control draw to a memory DC. You would have to override the WM_PAINT handler (and likely the WM_ERASEBKGND too), cause control to draw itself to a memory DC, add your own "owner" drawings to the memory DC, and then BitBlt the memory DC to a screen DC.

Some controls can tolerate being diverted to a memory DC. Some do not.

Arthur V. Ratz 21-Mar-16 2:31am

5.

Arthur V. Ratz 20-Mar-16 11:20am

Anyway in this case you have to handle a WM_PAINT AND WM_ERASEBKGND messages in your application. This gives you a handle to a valid device-context object.

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KarstenK · Answer 1 · 2016-03-22T01:17:00

Your drawing code belongs in the OnPaint() function. At first make the default call and than your stuff.

C++

void CHtmlEditCtrlEx::OnPaint()
{
  CWnd::OnPaint();

  //here comes your drawing code
  DrawSquigly(...);
}

For controlling the drawing you should use a member variable activated in the WM_RBUTTONUP message.