您的位置：首页 > 其它

INFO: Font Metrics and the Use of Negative lfHeight

2013-12-24 10:51 573 查看

INFO: Font Metrics and the Use of Negative lfHeight

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

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

内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理

标签：

相关文章推荐

新的分享

章节导航

INFO: Font Metrics and the Use of Negative lfHeight