wglUseFontBitmapsA function (wingdi.h)

Article
02/09/2023

The wglUseFontBitmaps function creates a set of bitmap display lists for use in the current OpenGL rendering context. The set of bitmap display lists is based on the glyphs in the currently selected font in the device context. You can then use bitmaps to draw characters in an OpenGL image.

The wglUseFontBitmaps function creates count display lists, one for each of a run of count glyphs that begins with the first glyph in the hdc parameter's selected fonts.

Syntax

BOOL wglUseFontBitmapsA(
  HDC   unnamedParam1,
  DWORD unnamedParam2,
  DWORD unnamedParam3,
  DWORD unnamedParam4
);

Parameters

unnamedParam1

Specifies the device context whose currently selected font will be used to form the glyph bitmap display lists in the current OpenGL rendering context.

unnamedParam2

Specifies the first glyph in the run of glyphs that will be used to form glyph bitmap display lists.

unnamedParam3

Specifies the number of glyphs in the run of glyphs that will be used to form glyph bitmap display lists. The function creates count display lists, one for each glyph in the run.

unnamedParam4

Specifies a starting display list.

Return value

If the function succeeds, the return value is TRUE.

If the function fails, the return value is FALSE. To get extended error information, call GetLastError.

Remarks

The wglUseFontBitmaps function defines count display lists in the current OpenGL rendering context. Each display list has an identifying number, starting at listBase. Each display list consists of a single call to glBitmap. The definition of bitmap listBase + i is taken from the glyph first + i of the font currently selected in the device context specified by hdc. If a glyph is not defined, then the function defines an empty display list for it.

The wglUseFontBitmaps function creates bitmap text in the plane of the screen. It enables the labeling of objects in OpenGL.

In the current version of Microsoft's implementation of OpenGL, you cannot make GDI calls to a device context that has a double-buffered pixel format. Therefore, you cannot use the GDI fonts and text functions with such device contexts. You can use the wglUseFontBitmaps function to circumvent this limitation and draw text in a double-buffered device context.

The function determines the parameters of each call to glBitmap as follows.

glBitmap Parameter	Meaning
width	The width of the glyph's bitmap, as returned in the gmBlackBoxX member of the glyph's GLYPHMETRICS structure.
height	The height of the glyph's bitmap, as returned in the gmBlackBoxY member of the glyph's GLYPHMETRICS structure.
xorig	The x offset of the glyph's origin, as returned in the gmptGlyphOrigin.x member of the glyph's GLYPHMETRICS structure.
yorig	The y offset of the glyph's origin, as returned in the gmptGlyphOrigin.y member of the glyph's GLYPHMETRICS structure.
xmove	The horizontal distance to the origin of the next character cell, as returned in the gmCellIncX member of the glyph's GLYPHMETRICS structure.
ymove	The vertical distance to the origin of the next character cell as returned in the gmCellIncY member of the glyph's GLYPHMETRICS structure.
bitmap	The bitmap for the glyph, as returned by GetGlyphOutline with uFormat equal to 1.

Examples

The following code example shows how to use wglUseFontBitmaps to draw some text.

HDC    hdc; 
HGLRC  hglrc; 
 
// create a rendering context  
hglrc = wglCreateContext (hdc); 
 
// make it the calling thread's current rendering context  
wglMakeCurrent (hdc, hglrc); 
 
// now we can call OpenGL API  
 
// make the system font the device context's selected font  
SelectObject (hdc, GetStockObject (SYSTEM_FONT)); 
 
// create the bitmap display lists  
// we're making images of glyphs 0 thru 254  
// the display list numbering starts at 1000, an arbitrary choice  
wglUseFontBitmaps (hdc, 0, 255, 1000); 
 
// display a string:  
// indicate start of glyph display lists  
glListBase (1000); 
// now draw the characters in a string  
glCallLists (24, GL_UNSIGNED_BYTE, "Hello Windows OpenGL World");

Note

The wingdi.h header defines wglUseFontBitmaps as an alias that automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that is not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	wingdi.h
Library	Opengl32.lib
DLL	Opengl32.dll

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