DOCUMENT:Q32667  15-JUL-1999  [win16sdk]
TITLE   :INFO: Font Metrics and the Use of Negative lfHeight
PRODUCT :Microsoft Windows Software Development Kit
PROD/VER:WINDOWS:3.1
OPER/SYS:
KEYWORDS:_IK kbSDKWin16

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Windows Software Development Kit (SDK) 3.1 
-------------------------------------------------------------------------------


SUMMARY
=======

The following illustrations show the most commonly used font metrics, including
Character Height, which is selected with negative values of each illustration is
followed by notes describing the metrics.

 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

                     O    O
 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

                       /\ 
                      /  \ 
                     /    \ 
 _ _ _ _ _ _ _ _ _  /______\ _ _ _ ___   _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
                   /        \     /   \|
                  /          \   |     |
 _ _ _ _ _ _ _ _ /_ _ _ _ _ _ \ _ \___/| _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
                                       |
                                       |
 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _\___/_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
                                                      |
                                                      |- External Leading
 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _
                                                      |
                     O    O                           |- Internal Leading
 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _
              |        /\ 
              |       /  \ 
              |      /    \ 
              |     /______\ _ _ _ ___   _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
 Char Height -|    /        \     /   \|
              |   /          \   |     |
              |  /_ _ _ _ _ _ \ _ \___/| _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
              |                        |
              |                        |
 _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _\___/_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

              |                                           |
              |      O    O                               |
              |                                           |
              |        /\                                 |
              |       /  \                                |
              |      /    \                               |- Ascent
 Cell Height -|     /______\       ___                    |
              |    /        \     /   \|                  |
              |   /          \   |     |                  |
              |  /_ _ _ _ _ _ \ _ \___/| _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _
              |                        |                  |
              |                        |                  |- Descent
 _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _\___/_ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _

Cell Height
-----------

This is the height selected on positive lfHeight in the LOGFONT. It is the height
of the font bitmap for raster fonts. It is returned as tmHeight in the
TEXTMETRIC structure from GetTextMetrics().

Character Height (Also Known as Em)
-----------------------------------

This is the height selected on negative lfHeight in the LOGFONT. (That is, the
mapper will try to match a font whose character height matches the absolute
value of the requested height.)

NOTE: By definition, the Em is equal to Cell Height minus Internal Leading. The
Em defines the point size of a font. In MM_TEXT mapping mode, the Em is related
to the point size as follows:

      Em=dpiY*point_size/72;  // where dpiY is dots per inch in Y direction

The dpiY of a font is equal to tmDigitizedAspectY in the TEXTMETRICS structure.

Internal Leading
----------------

This is returned as tmInternalLeading in the TEXTMETRIC structure from
GetTextMetrics() and often, but not necessarily, describes how much space has
been left inside the font bitmap for diacritical marks (accents).

External Leading
----------------

This is returned as tmExternalLeading in the TEXTMETRIC structure from
GetTextMetrics() and describes how much extra space the font designer expects
the application to leave between rows of the font. It is not included in the
bitmap and is not modified by TextOut()/ExtTextOut(), even in OPAQUE mode. When
outputting multiple lines of text, the lines should be separated by (tmHeight +
tmExternalLeading).

 Character Width                       Character Width
        |                                     |
 |-------------|                       |-------------|
 |          |                         /          /   |
 |          |                        /          /    |
 |          |                       /          /     |
 |          |                      /          /      |
 |----------|                     /----------/       |
 |          |                    /          /        |
 |          |                   /          /         |
 |          |                  /          /          |
 |          |                 /          /           |
                                            |________|
 |_____________|              |_____________|    |
        |                            |           Overhang
   Character width        Character width
 (including white space)  (including white space)
   Overhang = 0                  Overhang > 0

Overhang
--------

tmOverhang specifies the per string extra width that may be added to some
synthesized fonts. When synthesizing some attributes such as bold or italic, GDI
or a device may have to add width to a string on both a per character and per
string basis. For example, GDI synthesizes embolding by expanding the
intercharacter spacing and overstriking with an offset and italicizes a font by
skewing the string.

In either case, there is an overhang past the basic string. For bold strings, it
is the distance by which the overstrike is offset. For italic strings, it is the
amount the top of the font is skewed past the bottom of the font. tmOverhang
allows the application to determine how much of the character width returned by
a GetTextExtent() call on a single character is the actual character width and
how much is the per string extra width. The actual width is the extent less the
overhang. In other words, tmOverhang is the difference between the width of a
character when it is output singly versus its width when it is in the interior
of a string.

For more information, look up the following topics in the Windows Software
Development Kit reference:

 - CreateFont() (in Volume 1 of the version 3.0 reference)

 - TEXTMETRIC (in Volume 2 of the version 3.0 reference)

Additional query words: fonts metrics lfHeight height TEXTMETRIC EXTTEXTMETRIC LOGFONT 3.00 3.10

======================================================================
Keywords          : _IK kbSDKWin16 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1999.