2D OpenGL text rendering with existing app

[bytebucket]

I have an existing C++ MFC app which renders to a 3D OpenGL view.

I'd like to use Qt to render 2D text over the 3D scene. I found the below example and have been looking through it.

http://qt.nokia.com/doc/4.6/opengl-2dpainting.html

My question is, how do I setup Qt to render to my existing OpenGL context? I don't want Qt to create a new context for me I already have a context and I want Qt to render to my existing context.

The example seems to come down to the QGLContext class. But I didn't see any way to initialize that class to point to an existing GL context.

Basically, although I don't want to convert everything over to Qt yet, I'd like to use Qt to render 2D text within my current application framework (C++ MFC).

[john_god]

My question is, how do I setup Qt to render to my existing OpenGL context?

I don't know, but if your main goal is just to write 2D text to your 3D scene than you can use the code below, is from an example of the "Opengl Superbible" book. It works fine with me. Also you can check this site, lots of information about opengl and Qt.

Basically, although I don't want to convert everything over to Qt yet, I'd like to use Qt to render 2D text within my current application framework (C++ MFC).

MFC ... I've been there and since I meet Qt never use it again

#define MAX_STRING	1024
 
GLuint	SmallFont,		/* Small raster font */
		SymbolFont,    /*symbol font*/
		MediumFont,		/* Medium raster font */
		LargeFont;		/* Large raster font */
 
 
GLuint	FontCreateBitmaps(HDC hdc, char *typeface, int height,
		                  int weight, DWORD italic);
GLuint	FontCreateOutlines(HDC hdc, char *typeface, int height,
		                   int weight, DWORD italic);
void	FontDelete(GLuint font);
 
void	FontPrintf(GLuint font, char *format, ...);
void	FontPuts(GLuint font, char *s);
 
 
 
GLuint
FontCreateBitmaps(HDC   hdc,		/* I - Device Context */
                  char  *typeface,	/* I - Font specification */
                  int   height,		/* I - Font height/size in pixels */
	          int   weight,		/* I - Weight of font (bold, etc) */
	          DWORD italic)		/* I - Text is italic */
{
  GLuint	base;			/* Base display list for font */
  HFONT		font;			/* Windows font ID */
 
 
  //if ((base = glGenLists(96)) == 0)
  if ((base = glGenLists(224)) == 0)
	  return (0);
 
  if (stricmp(typeface, "symbol") == 0)
    font = CreateFont(height, 0, 0, 0, weight, italic, FALSE, FALSE,
                      SYMBOL_CHARSET, OUT_TT_PRECIS,
                      CLIP_DEFAULT_PRECIS, DRAFT_QUALITY,
                      DEFAULT_PITCH, typeface);
  else
    font = CreateFont(height, 0, 0, 0, weight, italic, FALSE, FALSE,
                      ANSI_CHARSET, OUT_TT_PRECIS,
                      CLIP_DEFAULT_PRECIS, DRAFT_QUALITY,
                      DEFAULT_PITCH, typeface);
 
  /*font = CreateFont(height, 0, 0, 0, weight, italic, FALSE, FALSE,
                      UNICODE_CHARSET, OUT_TT_PRECIS,
                      CLIP_DEFAULT_PRECIS, DRAFT_QUALITY,
                      DEFAULT_PITCH, typeface);
*/
  SelectObject(hdc, font);
 
  //wglUseFontBitmaps(hdc, 32, 96, base);
  wglUseFontBitmaps(hdc, 32, 224, base);
 
  return (base);
}
 
 
/*
 * 'FontDelete()' - Delete the OpenGL display lists used for a font.
 */
 
void
FontDelete(GLuint font)	/* I - Font to delete */
{
  if (font == 0)
    return;
 
 // glDeleteLists(font, 96);
  glDeleteLists(font, 224);
}
 
 
/*
 * 'FontPuts()' - Display a string using the specified font.
 */
 
void
FontPuts(GLuint font,	/* I - Font to use */
         char   *s)	/* I - String to display */
{
  if (font == 0)
    return;
 
  if (s == NULL)
    return;
 
  glPushAttrib(GL_LIST_BIT);
    glListBase(font - 32);
    glCallLists(strlen(s), GL_UNSIGNED_BYTE, s);
  glPopAttrib();
}
 
 
 
/*
 * 'FontPrintf()' - Display a formatted string using the specified font.
 */
 
void
FontPrintf(GLuint font,		/* I - Font to use */
           char   *format,	/* I - printf() style format string */
           ...)			/* I - Other arguments as necessary */
{
  va_list	ap;			/* Argument pointer */
  char		s[MAX_STRING + 1];	/* Output string */
 
 
  if (format == NULL)
    return;
 
  va_start(ap, format);
  vsprintf(s, format, ap);
  va_end(ap);
 
  FontPuts(font, s);
}
 
 
//finnally to draw the text inside your function
 
{
	SmallFont  = FontCreateBitmaps(m_hDC, "Courier", 12,  FW_BOLD, 0);
	double x=10;
	double y=20;
	double z=15;
 
	glRasterPos3d(x , y, z);
	FontPuts(SmallFont, "-x");	
 
}

#define MAX_STRING	1024

GLuint	SmallFont,		/* Small raster font */
		SymbolFont,    /*symbol font*/
		MediumFont,		/* Medium raster font */
		LargeFont;		/* Large raster font */


GLuint	FontCreateBitmaps(HDC hdc, char *typeface, int height,
		                  int weight, DWORD italic);
GLuint	FontCreateOutlines(HDC hdc, char *typeface, int height,
		                   int weight, DWORD italic);
void	FontDelete(GLuint font);

void	FontPrintf(GLuint font, char *format, ...);
void	FontPuts(GLuint font, char *s);



GLuint
FontCreateBitmaps(HDC   hdc,		/* I - Device Context */
                  char  *typeface,	/* I - Font specification */
                  int   height,		/* I - Font height/size in pixels */
	          int   weight,		/* I - Weight of font (bold, etc) */
	          DWORD italic)		/* I - Text is italic */
{
  GLuint	base;			/* Base display list for font */
  HFONT		font;			/* Windows font ID */

  
  //if ((base = glGenLists(96)) == 0)
  if ((base = glGenLists(224)) == 0)
	  return (0);

  if (stricmp(typeface, "symbol") == 0)
    font = CreateFont(height, 0, 0, 0, weight, italic, FALSE, FALSE,
                      SYMBOL_CHARSET, OUT_TT_PRECIS,
                      CLIP_DEFAULT_PRECIS, DRAFT_QUALITY,
                      DEFAULT_PITCH, typeface);
  else
    font = CreateFont(height, 0, 0, 0, weight, italic, FALSE, FALSE,
                      ANSI_CHARSET, OUT_TT_PRECIS,
                      CLIP_DEFAULT_PRECIS, DRAFT_QUALITY,
                      DEFAULT_PITCH, typeface);
  
  /*font = CreateFont(height, 0, 0, 0, weight, italic, FALSE, FALSE,
                      UNICODE_CHARSET, OUT_TT_PRECIS,
                      CLIP_DEFAULT_PRECIS, DRAFT_QUALITY,
                      DEFAULT_PITCH, typeface);
*/
  SelectObject(hdc, font);
  
  //wglUseFontBitmaps(hdc, 32, 96, base);
  wglUseFontBitmaps(hdc, 32, 224, base);

  return (base);
}


/*
 * 'FontDelete()' - Delete the OpenGL display lists used for a font.
 */

void
FontDelete(GLuint font)	/* I - Font to delete */
{
  if (font == 0)
    return;

 // glDeleteLists(font, 96);
  glDeleteLists(font, 224);
}


/*
 * 'FontPuts()' - Display a string using the specified font.
 */

void
FontPuts(GLuint font,	/* I - Font to use */
         char   *s)	/* I - String to display */
{
  if (font == 0)
    return;

  if (s == NULL)
    return;

  glPushAttrib(GL_LIST_BIT);
    glListBase(font - 32);
    glCallLists(strlen(s), GL_UNSIGNED_BYTE, s);
  glPopAttrib();
}



/*
 * 'FontPrintf()' - Display a formatted string using the specified font.
 */

void
FontPrintf(GLuint font,		/* I - Font to use */
           char   *format,	/* I - printf() style format string */
           ...)			/* I - Other arguments as necessary */
{
  va_list	ap;			/* Argument pointer */
  char		s[MAX_STRING + 1];	/* Output string */


  if (format == NULL)
    return;

  va_start(ap, format);
  vsprintf(s, format, ap);
  va_end(ap);

  FontPuts(font, s);
}


//finnally to draw the text inside your function

{
	SmallFont  = FontCreateBitmaps(m_hDC, "Courier", 12,  FW_BOLD, 0);
	double x=10;
	double y=20;
	double z=15;
	
	glRasterPos3d(x , y, z);
	FontPuts(SmallFont, "-x");	

}

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[bytebucket]

if your main goal is just to write 2D text to your 3D scene than you can use the code below

My experience with the GL text output methods you referred to is that you don't get anti-aliasing and so the text doesn't look very good.

MFC ... I've been there and since I meet Qt never use it again

That's great, and perhaps thats eventually the way to go. But from a standpoint of cost, I was hoping I could have Qt perform OpenGL rendering using my existing GL rendering context. I mentioned MFC for completeness, but really, the question is that I have a GL rendering context setup and ready to render, so how do I get Qt to just use that and do its GL rendering.

I've seen examples of Qt doing 2D rendering in OpenGL and it looks FAR nicer than what I've achieved using the font techniques you included in your reply. So I'm wondering how I can leverage that Qt OpenGL rendering in my existing app.

[john_god]

I dont think this will work for you, but in a QGLWidget I actually just render 2D text with

QFont font;
    font.setPointSize(10);   
    renderText(x,y,z,"some text",font);

QFont font;
    font.setPointSize(10);   
    renderText(x,y,z,"some text",font);

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this is somewath powerfull because QFont gives a lot of text format options. I have no experience in using Qt with MFC, I am assuming you're using visual studio integration, so I dont know if this renderText will work for you. Good look.

[bytebucket]

I noticed that sort of text rendering code in the 2D GL example. But if you look at the other classes involved you end up needing a QGLContext class which houses the OpenGL rendering context.

The problem is, I can't see a way to tell QGLContext to just use my existing context.

MFC is not the issue and I don't think the issue has anything to do with MFC.

Its just that I have already setup an OpenGL rendering context and I'd like Qt to render using that context. Getting Qt to render GL seems to hinge on the QGLContext class, but I'm not sure how to set that up to use an existing GL context.

[john_god]

Perhaps a workaround would be to use Qt opengl context to render text to a image, than import that image to your current gl context. Of course this could have performance issues.
Or depending the dimension of your project, with more or less work, you could instead of triyng to draw to an existent context, adapt your existent gl methods to draw to the Qt opengl context.

[bytebucket]

Maybe that's what I need to try -- See if I can just use Qt to create the GL rendering context instead of doing it directly with Windows APIs. I suspect that to create a Qt context it expects to create its own windowing surface as well. So the question just migrates to, ok how do I create a Qt GL context attached to my own window I'll take a look at it and see what I can find. If that doesn't work then maybe I'd have to have Qt create the window for me which might get messy because currently MFC creates the window. Not impossible I guess. Time to see how far down the rabbit hole this will go!

Certainly for a new application (or if there was unlimited time and resources) just doing it all with Qt would be cleaner. I'm hoping I can leverage Qt for some snazzy GL rendering without some major conversion or overhaul of an existing app though.

[john_god]

I just remember some months ago googling the web I find some librarys do draw text in opengl. Dont remember witch library or witch site but perhaps
you can find other ways to display better quality text than the methods of the previews posts. Than you would avoid messing with qt gl context.