Painting Text above OpenGL context in MFC - opengl

Question

I work on an MFC app containing OpenGL context.I am new to MFC that is why I am asking it.OpenGL works fine ,but when I want to draw a text above the 3D window using this code inside WindowProc:
case WM_PAINT:
hDC=BeginPaint(window,&paintStr);
GetClientRect(window,&aRect);
SetBkMode(hDC,TRANSPARENT);
DrawText(hDC,L"He He I am a text on top of OpenGL",-1,&aRect,DT_SINGLELINE|DT_CENTER|DT_VCENTER);
EndPaint(window,&paintStr);
return 0;
it is shown beneath the OpenGL context.I can see it only when resizing the window as the OpenGL rendering pauses than.

Answer 1

What you're doing is wrong and also harder than doing it all in OpenGL. To solve the problem of adding text to an OpenGL-drawn window, it's better to just make OpenGL draw the text. You can even use the exact same font you were using in MFC by creating a CFont instance when you handle WM_CREATE, selecting the font into the DC, and calling wglUseFontBitmaps, which will make a series of rasterized bitmaps that you can use with glCallLists. (While you're at it, call GetCharABCWidths and GetTextMetrics to determine the width and height of each glyph, respectively.)
ABC glyphInfo[256]; // for font widths
TEXTMETRIC tm; // for font heights
// create a bitmap font
CFont myFont;
myFont.CreateFont(
16, // nHeight
0, // nWidth
0, // nEscapement
0, // nOrientation
FW_NORMAL, // nWeight
FALSE, // bItalic
FALSE, // bUnderline
0, // cStrikeOut
ANSI_CHARSET, // nCharSet
OUT_DEFAULT_PRECIS, // nOutPrecision
CLIP_DEFAULT_PRECIS, // nClipPrecision
DEFAULT_QUALITY, // nQuality
DEFAULT_PITCH | FF_SWISS, // nPitchAndFamily
_T("Arial") // lpszFacename
);
// change the current font in the DC
CDC* pDC = CDC::FromHandle(hdc);
// make the system font the device context's selected font
CFont *pOldFont = (CFont *)pDC->SelectObject (&myFont);
// the display list numbering starts at 1000, an arbitrary choice
wglUseFontBitmaps (hdc, 0, 255, 1000);
VERIFY( GetCharABCWidths (hdc, 0, 255, &glyphInfo[0]) );
pDC->GetTextMetrics(&tm);
if(pOldFont)
pDC->SelectObject(pOldFont);
myFont.DeleteObject();
Then when you handle WM_PAINT, reset your matrices and use glRasterPos2d to put the text where you need it to go. I suggest calculating the exact width of your string using code similar to the one below if you want it to be horizontally centered.
// indicate start of glyph display lists
glListBase (1000);
CRect r;
GetWindowRect(r);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluOrtho2D(0, r.Width(), 0, r.Height());
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
CString formattedString;
formattedString.Format("Pi is about %1.2f", 3.1415);
int stringWidth=0; // pixels
for(int j=0; j < formattedString.GetLength(); ++j)
stringWidth += glyphInfo[ formattedString.GetAt(j) ].abcA + glyphInfo[ formattedString.GetAt(j) ].abcB + glyphInfo[ formattedString.GetAt(j) ].abcC;
double textXPosition, textYPosition;
textXPosition = r.Width()/2-stringWidth/2; // horizontally centered
textYPosition = r.Height()/2-tm.tmHeight/2; // vertically centered
glRasterPos2d(textXPosition,textYPosition);
// this is what actually draws the text (as a series of rasterized bitmaps)
glCallLists (formattedString.GetLength(), GL_UNSIGNED_BYTE, (LPCSTR)formattedString);
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
While the setup is annoying, you only have to do it once, and I think it's less frustrating than dealing with GDI. Mixing GDI and OpenGL is really asking for trouble, and OpenGL does a very good job of displaying text -- you get sub-pixel accuracy for free, among other benefits.
Edit: In response to your request for including GUI elements, I will assume that you meant that you want to have both OpenGL-drawn windows and also standard Windows controls (edit boxes, check boxes, buttons, list controls, etc.) inside the same parent window. I will also assume that you intend OpenGL to draw only part of the window, not the background of the window.
Since you said you're using MFC, I suggest that you create a dialog window, add all of your standard Windows controls to it, and then add in a CWnd-derived class where you handle WM_PAINT. Use the resource editor to move the control to where you want it. Effectively, you're making an owner-draw custom control where OpenGL is doing the drawing. So OpenGL will draw that window, and the standard MFC classes (CEdit, CButton, etc.) will draw themselves. This works well in my experience, and it's really not much different from what GDI does in an owner-draw control.
What if instead you want OpenGL to draw the background of the window, and you want standard Windows controls to appear on top of it? I don't think this is a great idea, but you can handle WM_PAINT and WM_ERASE for your CDialog-derived class. In WM_ERASE, call OpenGL to draw your 3D content, which will be overwritten by the standard Windows controls when WM_PAINT is called. Alternatively in WM_PAINT you could call OpenGL before calling CDialog::OnDraw, which would be similar.
Please clarify your statement "I want to add some 2s graphics overlay (like labels ,gui elements)" if you want me to write more.

Answer 2

Looking at your code I assume the OpenGL rendering is called from a timer or as idel loop action. Naturally OpenGL execution will probably contain some clearing, thus taking anything else drawn with it.
Mixing GDI text drawing with OpenGL is not recommended, but can be done. But of course you then need to include that code into the OpenGL drawing function, too, placing all GDI operations after the buffer swap.