When calling a font-creation function, an application describes the font either by using a LOGFONT structure in a call to the CreateFontIndirect function or by using the parameters of the CreateFont function. The font returned by these functions is called a logical font, because a font matching the described characteristics is not necessarily available in the system. GDI uses the logical font to create a physical font, by finding the closest match to the logical font among the available TrueType, raster, vector, and device-dependent fonts.
The Windows font mapper determines which of the available fonts is the closest match to the requested logical font. The font mapper often chooses a TrueType font as the closest match; it will choose a raster or vector font only when the logical font matches the characteristics of the raster or vector font very closely or when the logical font specifies the name of the raster or vector font. Typically, a TrueType font is chosen when it is specifically requested or when GDI would otherwise have to synthesize the font. For example, if a font name is not specified in the logical font or if the specified name does not exist, the font mapper chooses a TrueType font that matches the requested point size, serif characteristics, and pitch.
When the font mapper determines that a TrueType font is the closest match for a requested logical font, the TrueType engine produces enhanced GDI raster characters that are presented to the raster device. (The characters are enhanced by the use of ABC character widths.) For devices that do not have raster font capabilities, the driver must request the TrueType engine to provide the glyphs in a form the driver can use.
When the font mapper chooses between raster fonts, it chooses the font that is closest to the requested size without being larger than that size.
When an application requests a very small font, the font mapper may choose one of the small fonts stored in the SMALLX.FON font resource file. TrueType fonts specify a suggested minimum size, which can be retrieved by calling the GetOutlineTextMetrics function and checking the otmusMinimumPPEM member of the OUTLINETEXTMETRIC structure. When an application requests a font smaller than this size, the font mapper typically chooses a small font instead of a TrueType font. If the requested size is not available as a small font, however, GDI scales the TrueType font instead. Microsoft's 13 core TrueType fonts are designed to be readable as small as 8 points on a VGA screen, although they can be used at smaller sizes.