◄Up► ◄Next► ◄Previous►
────────────────────────────────────────────────────────────────────────────
 
A printer driver provides support for the various fonts provided or
supported by GDI.
 
Big Fonts
 
Some printer drivers use a new format for fonts when running in protected
mode (with Windows running in either standard or 386 enhanced mode) on an
80386 or 80486-based computer. This format allows for fonts that can exceed
64K bytes of data, as well as some other options. In this situation, GDI
will convert all the 2.x format fonts to the new format so that only one
font file format is used in memory.
 
If a printer driver prints GDI bitmap fonts directly, it should be modified
to handle big fonts. In many cases, a driver will not need to be updated if
it is a banding monochrome driver that uses only the brute functions. The
brute functions are already aware of the new format. For more information
about brute functions, see Section 4.1.25 "The Brute Functions," later in
this topic.
 
If a printer driver uses the color library, the library supports the big
font format, as well as the old 2.x format.
 
TrueType
 
GDI provides TrueType support for any driver that supports GDI raster fonts
(that is, it supports drivers that set the DT_RASPRINTER value in the
dpTechnology member of the GDIINFO structure). To support TrueType on these
printers, GDI generates a raster font from the TrueType outlines and passes
the font to the driver just as with any other raster font. This means many
Windows 3.0 printer drivers, especially drivers for dot-matrix printers,
currently support TrueType──no code changes in the driver are required.
 
Printer drivers that do not support raster fonts must be modified to support
TrueType. Typically, the modification consists of adding code to convert
TrueType fonts into a downloadable font format that the printer accepts. To
simplify the task of adding TrueType support to nonraster printer drivers,
GDI provides several TrueType service functions.
 
TrueType Service Functions
 
Printer drivers can use TrueType service functions to retrieve information
about TrueType fonts, to retrieve bitmaps of individual glyphs in the fonts,
and to realize a complete font, retrieving both information and bitmaps.
Following are the service functions and brief descriptions.
 
Function              Description
────────────────────────────────────────────────────────────────────────────
EngineDeleteFont      Deletes a realized TrueType font.
 
EngineEnumerateFont   Enumerates TrueType fonts.
 
EngineGetCharWidth    Retrieves character widths for TrueType fonts.
 
EngineGetGlyphBmp     Retrieves the bitmap for a rasterized glyph.
 
EngineRealizeFont     Realizes a TrueType font.
 
EngineSetFontContext  Sets the context for rasterizing glyphs.
 
GetRasterizerCaps     Specifies whether TrueType is available.
 
A printer driver can determine whether TrueType is currently available by
calling the GetRasterizerCaps function. Since users can turn TrueType off,
it is important that a driver check for TrueType before generating output.
 
If TrueType is on, the driver can call the EngineEnumFonts function whenever
GDI calls the driver's EnumDFonts function. This gives the font engine the
chance to enumerate the TrueType fonts having the specified font. The driver
can call the EngineRealizeFont function whenever GDI calls the driver's
RealizeObject function. This gives the TrueType font engine an opportunity
to generate a physical font that matches the specified logical font. When
the engine realizes a font, it fills a FONTINFO structure with information
about the font as well as the bitmap data for the individual glyphs. A
driver can use this information to create a downloadable font in the format
recognized by the printer.
 
In general, a printer driver should call the EngineRealizeFont and
EngineEnumerateFont functions before processing its own device fonts (if
any). If GDI requests that the driver delete a realized TrueType font (by
calling RealizeObject), the driver must call the EngineDeleteFont function
to delete the font.
 
A printer driver can retrieve character width information for a realized
TrueType font by using the EngineGetCharWidth function. It can retrieve
bitmaps for individual glyphs in the font by using the EngineSetFontContext
and EngineGetGlyphBmp functions. The driver must call EngineSetFontContext
first to set the font before calling EngineGetGlyphBmp. Drivers for printers
that accept individual glyph definitions (as opposed to full font
definitions) can use the character width information and bitmap data to
download individual glyphs.
 
Specifying the Spot Size
 
The spot size is a set of values that help the TrueType rasterizer create
the best glyph bitmaps for a given printer. All printer drivers can benefit
by setting the spot size in their GDIINFO structure regardless of whether
the driver uses TrueType service functions. The spot size should be
specified in the dpSpotSizeX and dpSpotSizeY members of the driver's
GDIINFO structure. If these members are not zero, GDI passes the values to
the TrueType engine to help it rasterize glyphs.
 
 
                                      ♦