File: metricsview.html

package info (click to toggle)
fontforge 1%3A20161005~dfsg-4%2Bdeb9u1
links: PTS, VCS
area: main
in suites: stretch
size: 69,324 kB
ctags: 44,030
sloc: ansic: 578,448; python: 5,546; sh: 3,374; makefile: 1,323; perl: 315; cpp: 176; ruby: 95; objc: 92; xml: 90; sed: 9
file content (825 lines) | stat: -rw-r--r-- 27,226 bytes
parent folder | download | duplicates (2)
<HTML>
<HEAD>
  <!-- Created with AOLpress/2.0 -->
  <!-- AP: Created on: 6-Dec-2000 -->
  <!-- AP: Last modified: 11-Nov-2009 -->
  <TITLE>The Metrics View</TITLE>
  <LINK REL="icon" href="fftype16.png">
  <LINK REL="stylesheet" TYPE="text/css" HREF="FontForge.css">
</HEAD>
<BODY id="menued">
<P ALIGN=CENTER>
<IMG SRC="fontforge-banner-420.jpeg" WIDTH=420 HEIGHT=80>
<DIV class="menucontainer">
  <UL class="menubar">
    <LI class="menu">
      <A href="http://sourceforge.net/projects/fontforge/files/">Download</A>
      <UL>
	<LI>
	  <A href="http://sourceforge.net/projects/fontforge/files/fontforge-docs/"
	      >Documentation</A>
	<LI>
	  <A href="http://sourceforge.net/projects/fontforge/files/fontforge-source/"
	      >Source</A>
      </UL>
    <LI>
      <A HREF="overview.html#TOC">Introduction</A>
    <LI>
      <A href="editexample.html">Tutorial</A>
    <LI class="menu">
      <A href="fontview.html">Windows</A>
      <UL>
	<LI>
	  <A href="fontview.html" >Font</A>
	<LI>
	  <A href="charview.html" >Outline Glyph</A>
	<LI>
	  <SMALL><A href="charview.html#Debugging" >&nbsp; &nbsp;Debugging
	  TrueType</A></SMALL>
	<LI>
	  <SMALL><A href="multilayer.html" >&nbsp; &nbsp;Type3 Glyphs</A></SMALL>
	<LI>
	  <A href="bitmapview.html" >Bitmap Glyph</A>
	<LI>
	  <A href="metricsview.html" >Metrics</A>
      </UL>
    <LI class="menu">
      <A href="fontinfo.html">Dialogs 1</A>
      <UL>
	<LI>
	  <A href="fontinfo.html" >Font Information</A>
	<LI>
	  <SMALL><A href="histogram.html" >&nbsp; &nbsp;Histogram Dialog</A></SMALL>
	<LI>
	  <A href="charinfo.html" >Glyph Information</A>
	<LI>
	  <A href="getinfo.html" >Point, Reference Information</A>
	<LI>
	  <A href="multilayer.html#Layer" >Type3 Layer Information</A>
	<LI>
	  <A href="bdfinfo.html" >Bitmap Properties</A>
	<LI>
	  <A href="baseline.html" >Baseline Information</A>
	<LI>
	  <A HREF="justify.html">Justification Information</A>
	<LI>
	  <A href="math.html" >Math Information</A>
	<LI>
	  <A href="multiplemaster.html" >Multiple Master Information</A>
	<LI>
	    <HR>
	<LI>
	  <A href="lookups.html" >Lookups &amp; subtables</A>
	<LI>
	  <A href="metricsview.html#kernpair" >Kerning glyph pairs 1</A>
	<LI>
	  <A href="kernpairs.html" >Kerning glyph pairs 2</A>
	<LI>
	  <A href="metricsview.html#kernclass" >Kerning by classes</A>
	<LI>
	  <A href="anchorcontrol.html" >Anchor Control</A>
	<LI>
	  <A href="contextchain.html" >Contextual lookup dialog</A>
	<LI>
	  <A href="statemachine.html" >Apple State Machine dialog</A>
	<LI>
	  <A href="showatt.html" >Show Advanced Typography</A>
	<LI>
	    <HR>
	<LI>
	  <A href="problems.html" >Potential Problems dialog</A>
	<LI>
	  <A href="validation.html" >Font Validation dialog</A>
      </UL>
    <LI class="menu">
      <A href="generate.html">Dialogs 2</A>
      <UL>
	<LI>
	  <A href="filemenu.html#Open" >Open Fonts dialog</A>
	<LI>
	  <A href="oflib.html" >Browsing OFLib dialog</A>
	<LI>
	  <A href="generate.html" >Generate Fonts dialog</A>
	<LI>
	  <A href="generate.html#Mac" >Generate Mac Family dialog</A>
	<LI>
	    <HR>
	<LI>
	  <A href="display.html" >Print &amp; Display dialog</A>
	<LI>
	  <A href="prefs.html" >Preferences dialog</A>
	<LI>
	  <A href="groups.html" >Groups dialog</A>
	<LI>
	    <HR>
	<LI>
	  <A href="elementmenu.html#Bitmaps">Manage Bitmap Strikes</A>
	<LI>
	  <A href="elementmenu.html#Regenerate">Re-Rasterize Bitmap Strikes</A>
	<LI>
	    <HR>
	<LI>
	  <A href="search.html" >Search &amp; Replace dialog</A>
	<LI>
	  <A href="Styles.html" >Style Transformation dialogs</A>
	<LI>
	  <A href="transform.html" >Transformation dialog</A>
	<LI>
	  <A href="elementmenu.html#Expand" >Expand Stroke dialog</A>
	<LI>
	  <A href="tilepath.html" >Tile Path dialog</A>
	<LI>
	  <A href="InsertTextDlg.html" >Insert Text dialog</A>
	<LI>
	    <HR>
	<LI>
	  <A href="metricsmenu.html#Width">Set width dialogs</A>
	<LI>
	  <A href="metricsmenu.html#Width">Set left/right bearings</A>
	<LI>
	  <A href="autowidth.html" >Auto Width dialog</A>
	<LI>
	    <HR>
	<LI>
	  <A href="hintsmenu.html#Review" >Review PS Hints dialog</A>
	<LI>
	  <A href="ttfinstrs.html" >TrueType Instruction Editor</A>
	<LI>
	  <A href="ttfinstrs.html#cvt" >TrueType 'cvt ' Editor</A>
	<LI>
	    <HR>
	<LI>
	  <A href="selectbyatt.html" >Select by feature dialog</A>
	<LI>
	  <A href="elementmenu.html#MassRename" >Rename Glyphs dialog</A>
	<LI>
	  <A href="elementmenu.html#CompareFonts" >Compare Fonts dialog</A>
      </UL>
    <LI class="menu">
      <A href="filemenu.html">Menus</A>
      <UL>
	<LI>
	  <A href="filemenu.html" >File</A>
	<LI>
	  <A href="editmenu.html" >Edit</A>
	<LI>
	  <A href="pointmenu.html" >Point</A>
	<LI>
	  <A href="elementmenu.html">Element</A>
	<LI>
	  <A href="toolsmenu.html">Tools</A>
	<LI>
	  <A href="hintsmenu.html" >Hints</A>
	<LI>
	  <A href="encodingmenu.html" >Encoding</A>
	<LI>
	  <A href="viewmenu.html" >View</A>
	<LI>
	  <A href="metricsmenu.html" >Metrics</A>
	<LI>
	  <A href="cidmenu.html" >CID</A>
	<LI>
	  <A href="mmmenu.html" >Multi Master</A>
	<LI>
	  <A href="windowmenu.html" >Window</A>
	<LI>
	  <A href="helpmenu.html" >Help</A>
      </UL>
    <LI>
      <A href="faqFS.html">FAQ</A>
    <LI>
      <A href="IndexFS.html">Index</A>
    <LI>
      <A href="GlossaryFS.html">Glossary</A>
  </UL>
</DIV>
<DIV id="in">
  <H1 ALIGN=Center>
    The Metrics View
  </H1>
  <P>
  <IMG SRC="MetricsView.png" WIDTH="479" HEIGHT="331">
  <P>
  The metrics view allows you to examine how glyphs look together and to alter
  the spacing between them. You may apply various OpenType features to those
  glyphs and see how they are altered.
  <P>
  If the metrics view is created from the font view then any selected glyphs
  (well, the first 15 or so) will be displayed in the view in the order they
  were selected. If it is created from an outline or bitmap glyph view then
  only that glyph is displayed. If it is created from a bitmap glyph view (or
  from the font view when that view is displaying a bitmap font) then the metrics
  view will display bitmaps, but will not allow you to edit the bitmaps metrics
  (you must do your metrics editing in a view displaying outlines).
  <P>
  Underneath the menu bar is a series of fields. The first shows the current
  script and language combination being used to determine what lookups to apply
  within the selected features, the next is a text field which allows you to
  enter additional unicode characters to be displayed, and finally there is
  a pulldown list of lookup subtables, this will be used if you create a kerning
  pair (the kerning pair will become part of that subtable). Underneath that
  is a list showing all features defined in the font. You may select which
  ones you want to be active in this display. (Note the features are listed
  in alphabetic order -- this is not the order in which the lookups will be
  executed (or not usually the order)).
  <P>
  If you wish to enter characters you cannot type:
  <OL>
    <LI>
      Select the character (or glyph) in the fontview and then drag and drop it
      into the metrics view at the appropriate place
    <LI>
      Use the View menu to change or insert a character or glyph (View-&gt;Insert
      Glyph After)
    <LI>
      Select the characters individually and in order in the font view before you
      open the metrics view, when you do open it the characters will appear in
      the order you selected them
    <LI>
      FontForge has its own funky <A HREF="#Entering">input method</A>
  </OL>
  <P>
  The mid portion of the view is taken up with the displayed glyphs. For outline
  glyphs these are sized so that the em-height of the font just fits in this
  region. There are grey lines between the glyphs marking the origin of the
  glyph on the right and the width of the glyph on the left. The baseline is
  also drawn in grey.
  <P>
  A metrics view may be in one of three modes (Metrics-&gt;Window Type)
  <UL>
    <LI>
      Kerning only -- you may adjust the kerning between any pairs of glyphs shown,
      but you may not set any advance widths
    <LI>
      Advance Width only -- you may adjust the advance width of any glyph shown,
      but you may not set kerning
    <LI>
      Both -- see below
  </UL>
  <P>
  One of the glyphs is active. That glyph has a green line on its left (at
  its origin) and a blue line on its right (its width). You may change the
  width by dragging this line. You may change the left side bearing (lbearing)
  of the glyph by clicking on the glyph and dragging it left or right. You
  may change the kerning between this glyph and the one to its left by dragging
  the green line around. (If you wish to create a <A HREF="#DeviceTable">Device
  Table</A> for small pixel sizes you must use the
  <A HREF="metricsview.html#kernpair">Kern Pair Closeup dialog</A>)
  <TABLE BORDER CELLPADDING="2">
    <CAPTION>
      Kerning
    </CAPTION>
    <TR>
      <TD><IMG SRC="To-unkerned.png" WIDTH="204" HEIGHT="323"></TD>
      <TD><IMG SRC="To-kerned.png" WIDTH="204" HEIGHT="323"></TD>
    </TR>
  </TABLE>
  <P>
  The active glyph may be changed by clicking on any of the glyphs.
  <P>
  Underneath the display area are a set of text fields. You may type in new
  numbers for any of these fields to change the corresponding metrics of the
  glyph.
  <P>
  The up and down arrow keys will increase and decrease the field's value by 
  a single unit. Holding Shift-up or -down will accelerate this by 10 and 
  Ctrl-Shift-up or -down by 5.
  Holding Alt-up, -down, -left or -right will move the cursor to the field 
  above, below, left or right.
  <P>
  Sometimes it is handy to be able to load a list of words into the metrics
  view (so that you don't have to type them one by one). The text entry field
  has a pull down list, and at the bottom of this list is an entry to load
  a word list from a file. Once you select this, and your file, the pulldown
  list will ill up with choices. You may use the up/down arrow keys to move
  through the word list.
  <P>
  If the first glyph to be displayed is in Hebrew or Arabic (or any other right
  to left language) then the entire display area will be shown right to left
  <P>
  <STRONG>Note</STRONG> there is a very complicated algorithm given in the
  Unicode spec for displaying mixed right to left and left to right passages.
  This is not followed here. The direction determination is done by the first
  glyph alone.
  <P>
  <IMG SRC="VerticalMetrics.png" WIDTH="270" HEIGHT="573" ALIGN="Right"><IMG
      SRC="HebrewMetrics.png" WIDTH="511" HEIGHT="323">
  <P>
  You can make the window display vertical metrics and kerning by
  View-&gt;Vertical. (This is only available if your font has vertical metrics
  enabled, Element-&gt;Font Info-&gt;General-&gt;Has Vertical Metrics). In
  this mode you can change vertical width, vertical kerning, etc.
  <P>
  If you double click on one of the displayed glyphs then FontForge will bring
  up a outline glyph view to allow you to edit that glyph.
  <P>
  <IMG SRC="MetricsView-features.png" WIDTH="463" HEIGHT="330" ALIGN="Left"><BR
      CLEAR=RIGHT>
  In the example at left, the input text is an "f" followed by an "i", and
  as the 'liga' feature is turned on, this becomes the "fi" ligature. Then
  an "a" followed by a "b", but as the 'smcp' (small caps) feature is on these
  become small-caps letters rather than lower case. Finally "1", "/" and "2"
  were entered, and as the 'frac' (diagonal fractions) feature is turned on
  these three input glyphs become the onehalf glyph on output.
  <P>
  Note: This window is not a full blown layout engine. All the glyphs will
  be treated as if they were in the same script, and all features will be applied
  to all glyphs. Baseline alignment will not be done.<BR CLEAR=ALL>
  <H2>
    <A NAME="Entering">Entering non-ASCII characters</A>
  </H2>
  <P>
  Most of us are stuck with keyboards that only have ASCII characters on them.
  Or at best some sub-set of ISO 8859-1 characters. How can the full range
  of unicode characters be entered?
  <P>
  X supplies a sophisticated mechanism for entering characters via stand-alone
  <A HREF="xim.html">input method servers</A>. FontForge supports this to some
  extent now.
  <P>
  Aside from that, many versions of X supply a "Compose Character" key, or
  something equivalent. The X software will map a sequence of keystrokes to
  one character in whatever the native encoding may be.
  <P>
  My keyboard doesn't have such a key, and my X doesn't do this. But I have
  implemented something along those lines for those of us with less expensive
  keyboards. If you are in a mode where text entry is possible then press the
  F12 key and follow it by a series of keystrokes. Accented characters may
  be built using the following:
  <TABLE CELLPADDING="2">
    <TR>
      <TD>&nbsp;&nbsp;&nbsp;&nbsp;</TD>
      <TD>`</TD>
      <TD>grave accent</TD>
      <TD>&nbsp;&nbsp;&nbsp;&nbsp;</TD>
      <TD>0</TD>
      <TD>ring</TD>
      <TD>&nbsp;&nbsp;&nbsp;&nbsp;</TD>
      <TD>"</TD>
      <TD>double grave (or tonos)</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>'</TD>
      <TD>acute accent</TD>
      <TD></TD>
      <TD>/</TD>
      <TD>slash</TD>
      <TD></TD>
      <TD>.</TD>
      <TD>dot above</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>:</TD>
      <TD>diaeresis (umlaut)</TD>
      <TD></TD>
      <TD>7</TD>
      <TD>breve</TD>
      <TD></TD>
      <TD>,</TD>
      <TD>dot below</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>^</TD>
      <TD>circumflex</TD>
      <TD></TD>
      <TD>6</TD>
      <TD>caron</TD>
      <TD></TD>
      <TD>5</TD>
      <TD>cedilla</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>~</TD>
      <TD>tilde</TD>
      <TD></TD>
      <TD>_</TD>
      <TD>macron</TD>
      <TD></TD>
      <TD>4</TD>
      <TD>ogonec</TD>
    </TR>
  </TABLE>
  <P>
  So &Acirc; may be built by <KBD>[F12] ^ A</KBD>, and A with diaeresis and
  macron may be built with <KBD>[F12] : _ A</KBD>.
  <P>
  Greek letters may also be created. If you start with <KBD>[F12] @</KBD> and
  follow with:
  <TABLE CELLPADDING="2">
    <TR>
      <TD>&nbsp;&nbsp;&nbsp;</TD>
      <TD>A</TD>
      <TD>Alpha</TD>
      <TD>&nbsp;&nbsp;&nbsp;</TD>
      <TD>B</TD>
      <TD>Beta</TD>
      <TD>&nbsp;&nbsp;&nbsp;</TD>
      <TD>C</TD>
      <TD>Chi</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>D</TD>
      <TD>Delta</TD>
      <TD></TD>
      <TD>E</TD>
      <TD>Epsilon</TD>
      <TD></TD>
      <TD>F</TD>
      <TD>Phi</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>G</TD>
      <TD>Gamma</TD>
      <TD></TD>
      <TD>H</TD>
      <TD>Eta</TD>
      <TD></TD>
      <TD>I</TD>
      <TD>Iota</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>J</TD>
      <TD>(technical) Theta</TD>
      <TD></TD>
      <TD>K</TD>
      <TD>Kappa</TD>
      <TD></TD>
      <TD>L</TD>
      <TD>Lamda</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>M</TD>
      <TD>Mu</TD>
      <TD></TD>
      <TD>N</TD>
      <TD>Nu</TD>
      <TD></TD>
      <TD>O</TD>
      <TD>Omicron</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>P</TD>
      <TD>Pi</TD>
      <TD></TD>
      <TD>Q</TD>
      <TD>Theta</TD>
      <TD></TD>
      <TD>R</TD>
      <TD>Rho</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>S</TD>
      <TD>Sigma</TD>
      <TD></TD>
      <TD>T</TD>
      <TD>Tau</TD>
      <TD></TD>
      <TD>U</TD>
      <TD>Upsilon</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>V</TD>
      <TD>final sigma</TD>
      <TD></TD>
      <TD>W</TD>
      <TD>Omega</TD>
      <TD></TD>
      <TD>X</TD>
      <TD>Xi</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>Y</TD>
      <TD>Psi</TD>
      <TD></TD>
      <TD>Z</TD>
      <TD>Zeta</TD>
      <TD></TD>
      <TD></TD>
      <TD></TD>
    </TR>
  </TABLE>
  <P>
  This is the mapping used by the Symbol font. (Lower case letters are created
  similarly so <KBD>[F12] @ a</KBD> yields a lower case alpha). Accented greek
  letters may also be built up, <KBD>[F12] @ " A</KBD> yields Alpha tonos.
  <P>
  Finally the following special characters may be built:
  <TABLE CELLPADDING="2">
    <TR>
      <TD>&nbsp;&nbsp;&nbsp;</TD>
      <TD>[F12] &lt;space&gt;</TD>
      <TD>&lt;no break space&gt;</TD>
      <TD>&nbsp;&nbsp;&nbsp;</TD>
      <TD>[F12] *</TD>
      <TD>&#176;</TD>
      <TD>&nbsp;&nbsp;&nbsp;</TD>
      <TD>[F12] @ *</TD>
      <TD>&lt;bullet&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] @ &lt;space&gt;</TD>
      <TD>&lt;em space&gt;</TD>
      <TD></TD>
      <TD>[F12] #</TD>
      <TD>&#163;</TD>
      <TD></TD>
      <TD>[F12] @ #</TD>
      <TD>&#165;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] $</TD>
      <TD>&lt;euro&gt;</TD>
      <TD></TD>
      <TD>[F12] @ $</TD>
      <TD>&#162;</TD>
      <TD></TD>
      <TD>[F12] !</TD>
      <TD>&#161;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] +</TD>
      <TD>&#177;</TD>
      <TD></TD>
      <TD>[F12] -</TD>
      <TD>&lt;soft-hyphen&gt;</TD>
      <TD></TD>
      <TD>[F12] @ -</TD>
      <TD>&lt;en dash&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] @ .</TD>
      <TD>&#183;</TD>
      <TD></TD>
      <TD>[F12] 7 2</TD>
      <TD>&#189;</TD>
      <TD></TD>
      <TD>[F12] ;</TD>
      <TD>. . .</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] &lt;</TD>
      <TD>&lt;less or equal&gt;</TD>
      <TD></TD>
      <TD>[F12] &gt;</TD>
      <TD>&lt;greater or equal&gt;</TD>
      <TD></TD>
      <TD>[F12] @ &gt;</TD>
      <TD>&lt;triangle bullet&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] =</TD>
      <TD>&lt;quote dash&gt;</TD>
      <TD></TD>
      <TD>[F12] ?</TD>
      <TD>&#191;</TD>
      <TD></TD>
      <TD>[F12] A</TD>
      <TD>&Aring;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] C</TD>
      <TD>&Ccedil;</TD>
      <TD></TD>
      <TD>[F12] H</TD>
      <TD>&lt;right index&gt;</TD>
      <TD></TD>
      <TD>[F12] O</TD>
      <TD>&lt;OE lig&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] P</TD>
      <TD>&#167;</TD>
      <TD></TD>
      <TD>[F12] [</TD>
      <TD>&lt;single right quote&gt;</TD>
      <TD></TD>
      <TD>[F12] ]</TD>
      <TD>&lt;single right quote&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] \</TD>
      <TD>&#171;</TD>
      <TD></TD>
      <TD>[F12] @ \</TD>
      <TD>&lt;single guillemot&gt;</TD>
      <TD></TD>
      <TD>[F12] a</TD>
      <TD>&aring;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] c</TD>
      <TD>&ccedil;</TD>
      <TD></TD>
      <TD>[F12] f</TD>
      <TD>&lt;female sign&gt;</TD>
      <TD></TD>
      <TD>[F12] g</TD>
      <TD>&copy;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] h</TD>
      <TD>&lt;left index&gt;</TD>
      <TD></TD>
      <TD>[F12] m</TD>
      <TD>&lt;male sign&gt;</TD>
      <TD></TD>
      <TD>[F12] o</TD>
      <TD>&lt;oe lig&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] p</TD>
      <TD>&#182;</TD>
      <TD></TD>
      <TD>[F12] r</TD>
      <TD>&reg;</TD>
      <TD></TD>
      <TD>[F12] s</TD>
      <TD>&szlig;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] t</TD>
      <TD>TM</TD>
      <TD></TD>
      <TD>[F12] z</TD>
      <TD>&lt;long s&gt;</TD>
      <TD></TD>
      <TD>[F12] {</TD>
      <TD>&lt;left dbl quote&gt;</TD>
    </TR>
    <TR>
      <TD></TD>
      <TD>[F12] }</TD>
      <TD>&lt;right dbl quote&gt;</TD>
      <TD></TD>
      <TD>[F12] |</TD>
      <TD>&#187;</TD>
      <TD></TD>
      <TD>[F12] @ |</TD>
      <TD>&lt;right single guillemot&gt;</TD>
    </TR>
  </TABLE>
  <P>
  This still misses most unicode characters. But pressing [F12] twice will
  bring up a dialog which will allow you to select any character in unicode.
  <P>
  If you type [F12] by mistake then an Escape will get you out of accent mode.
  <H2>
    <A NAME="kernclass">Kerning By Class</A>
  </H2>
  <P>
  Often it is a good idea to create classes of glyphs which kern alike. For
  example A, &Agrave;, &Aacute;, &Acirc;, &Acirc;, &Atilde; and &Auml; probably
  all kern alike (but note that o and &ocirc; probably kern quite differently
  after a T), and rather than create separate kerning pairs for each of the
  "A"s above, they could all be placed in a class of glyphs which kern alike.
  <P>
  The <A HREF="lookups.html">Element-&gt;Font Info-&gt;Lookups</A> provides
  an interface to
  this.<IMG SRC="kerningformat.png" WIDTH="444" HEIGHT="704" ALIGN="Right">
  It brings up a dialog showing all the GPOS lookups (of which kerning is one)
  and their subtables. Each set of kerning classes lives in its own subtable.
  When you create a kerning subtable you will be asked whether you want a set
  of individual kerning pairs or a matrix based on kerning classes.
  <P>
  If you choose the latter then you may have fontforge try to guess a good
  set of classes for you (it will look at the glyphs selected and divide them
  into classes). The <CODE>Intra Class Distance</CODE> gives you some control
  over how picky fontforge will be about what goes into a class. (This can
  be thought of as being in em-units and being, roughly, the average error
  in how two different glyphs interact with other glyphs). A value of 1 is
  very picky and almost all classes will have one member. A value of 20 (in
  a 1000em font) is fairly loose.
  <P>
  The <CODE>Default Separation</CODE> and <CODE>Min Kern</CODE> fields are
  used in AutoKerning. The goal of kerning to to make the optical separation
  between all glyphs to be constant, and the <CODE>Default Separation
  </CODE>field specifies that desired value. The <CODE>Min Kern</CODE> value
  is simply to prevent the dialog from filling with useless junk. If AutoKerning
  suggests that two glyphs should be kerned by 1 em unit then this won't make
  any difference to the human eye and there is no point in including it. So
  if the kerning value (in absolute value) suggested by AutoKern is less than
  <CODE>Min Kern</CODE> then fontforge will ignore that value. Selecting <CODE>[]
  Touching</CODE> makes AutoKerning work in a slightly different way, instead
  of trying to make the optical distance be the desired value this attempts
  to make the minimum separation be the desired value (This is rarely useful,
  but occasionally people want to set text where the letters actually touch
  one another). The <CODE>[] Only kern glyphs closer </CODE>flag means that
  FontForge will only generate negative kerning offsets, that is, offsets which
  will move glyphs closer together.<BR clear="all">
  <P>
  <IMG SRC="kerningclass.png" WIDTH="1037" HEIGHT="588" ALIGN="Top">Each kerning
  class belongs to a <A HREF="lookups.html">lookup subtable</A> and the subtable
  name is displayed at the top of the dialog.
  <P>
  But the more interesting stuff follows this. A kerning by class actually
  consists of two sets of classes -- one set for the first glyph of the pair
  and one for the second glyph of the pair. A glyph class consists of a space
  separated list of glyph names (For most glyphs you may also enter the unicode
  character itself, and fontforge will convert that to a glyph name).
  <P>
  To edit a class, simply type in it (at the very bottom of the class list
  is an entry called <FONT COLOR="Blue">&lt;New&gt;</FONT>, clicking here will
  create a new class). Pressing the little rectangle at the right of the class
  will allow you to define your class as a selection in a font view widget.
  You may delete a class by selecting it (clicking in it) and pressing the
  [Delete] button.
  <P>
  The kerning classes can be fairly complex. You can search for a glyph by
  typing its name in the "Select Glyph" field. This will highlight the class
  containing that glyph.
  <P>
  Class 0 is usually magic. You almost never set it, it contains any glyphs
  not mentioned elsewhere. In OpenType, class 0 of the first character can
  be set and behaves normally.
  <P>
  Underneath the classes is a display of kerning values. The possible first
  glyph classes are listed vertically, the possible second glyph classes are
  listed horizontally. When you select a class (in one of the class lists above)
  the display of kerning values will scroll to display that class. If you move
  the mouse into the display and let it rest, a popup window will appear showing
  the glyphs that make up the classes which intersect at that point. If you
  click on a kerning value in the display, the dlg displays a visual representation
  of that amount of kerning.
  <P>
  The kerning dialog displays a representative glyph from each class and allows
  you to adjust the kerning between them (and all other class members of each
  class). You can select which glyphs to display in the pulldown menus. You
  can enter a new kerning offset by typing in a value, or you can click on
  the second glyph of the kern pair and drag it around.
  <P>
  You can also create something called a "<A NAME="DeviceTable">Device
  Table</A>", a name which is not very informative. When a font is rasterized
  at small pixel sizes rounding errors become important, and this is particularly
  true of kerning, there are three things that get rounded: The locations of
  the outlines (to fit them to a pixel grid), the advance widths of the glyphs,
  and the kerning value itself. The result is that something which looks perfectly
  kerned at 150pixels may be either too close or too far apart at 12pixels
  <TABLE ALIGN=CENTER CELLPADDING="2">
    <TR>
      <TD><IMG SRC="kern-We-150.png" WIDTH="170" HEIGHT="131"></TD>
      <TD><P ALIGN=Center>
	<IMG SRC="kern-We-12.png" WIDTH="32" HEIGHT="26"></TD>
    </TR>
    <TR VALIGN="Top">
      <TD><P ALIGN=Center>
	Kerning at 150 pixels</TD>
      <TD><P ALIGN=Center>
	Kerning at 12 pixels<BR>
	(magnified by 2)</TD>
    </TR>
  </TABLE>
  <P>
  You could adjust the kerning value slightly until it looked right at 12pixels,
  of course, but that might break it at 14 pixels. So OpenType has the concept
  of a Device Table which allows you to add small corrections at particular
  point sizes. Simply set the Display Size to a small, but common, value (say
  10-24) and examine the kerning. If the results are ugly then type a value
  into the "Device Table Correction" field, and this will change the spacing
  by that many pixels at the given display size (and no other). In the case
  above a correction of 1 might be appropriate for the 12px display.
  <P>
  Because small pixel sizes can be hard to examine, you can change the
  magnification (rasterized at the same size, but each pixel made twice as
  big).
  <P>
  <A HREF="metricsview.html#DeviceTable">Device Tables</A> may also be created
  in a number of other cases. The example above was for a kerning class.
  <A NAME="kernpair">Kerning pairs</A> may also have tables attached to them
  with the Metrics-&gt;Kern Pair Closeup dialog, which looks similar to the
  Kerning Class dialog above.
  <P ALIGN=Center>
  <IMG SRC="kernpairclose.png" WIDTH="560" HEIGHT="284">
  <P>
  <BR>
  <P>
  <P>
  <P ALIGN=Center>
  -- <A HREF="bitmapview.html">Prev</A> -- <A HREF="overview.html">TOC</A>
  -- <A HREF="filemenu.html">Next</A> --
</DIV>
</BODY></HTML>