wglUseFontBitmaps
[New
- Windows 95, OEM Service Release 2]
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.
BOOL wglUseFontBitmaps(
|
HDC hdc, |
// device
context whose font will be used |
|
DWORD first, |
// glyph
that is the first of a run of glyphs to be turned into bitmap display lists |
|
DWORD count, |
// number
of glyphs to turn into bitmap display lists |
|
DWORD listBase |
//
specifies starting display list |
|
); |
|
Parameters
hdc
Specifies the
device context whose currently selected font will be used to form the glyph
bitmap display lists in the current OpenGL rendering context.
first
Specifies the
first glyph in the run of glyphs that will be used to form glyph bitmap display
lists.
count
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.
listBase
Specifies a
starting display list.
Return Values
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 in Windows NT and
Windows 95, 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. |
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 255
// 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 Win32
OpenGL World");
See Also