INFO: Font Metrics and the Use of Negative lfHeight

9974 단어 height

INFO: Font Metrics and the Use of Negative lfHeight


 
Print
 Email
 
Article translations 
Article ID: 32667 - 
View products that this article applies to.
Retired KB Content Disclaimer
This article was previously published under Q32667
Expand all | 
Collapse all

On This Page

  • SUMMARY
  • Cell Height
  • Character Height (Also Known as Em)
  • Internal Leading
  • External Leading
  • Overhang

  • Properties
  • Give Feedback

  • 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)

  • Back to the top
     | 
    Give Feedback

    Properties


    Article ID: 32667 - Last Review: March 21, 2005 - Revision: 1.1
    APPLIES TO
  • Microsoft Windows Software Development Kit 3.1

  • Keywords: 
    kbinfo KB32667
    Retired KB Content Disclaimer
    This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is"and will no longer be updated.
    Back to the top
     | 
    Give Feedback

    좋은 웹페이지 즐겨찾기