org.extex.font.format.xtf.tables
Class TtfTableLTSH

java.lang.Object
  org.extex.font.format.xtf.tables.AbstractXtfTable
      org.extex.font.format.xtf.tables.TtfTableLTSH

All Implemented Interfaces:

XtfGlyphName, XtfTable, XMLWriterConvertible

public class TtfTableLTSH
extends AbstractXtfTable
implements XtfTable, XMLWriterConvertible

The table 'LTSH' (The Linear Threshold Table).

The LTSH table relates to OpenType fonts containing TrueType outlines. There are noticeable improvements to fonts on the screen when instructions are carefully applied to the sidebearings. The gain in readability is offset by the necessity for the OS to grid fit the glyphs in order to find the actual advance width for the glyphs (since instructions may be moving the sidebearing points). The TrueType outline format already has two mechanisms to side step the speed issues: the 'hdmx' table, where precomputed advance widths may be saved for selected ppem sizes, and the 'vdmx' table, where precomputed vertical advance widths may be saved for selected ppem sizes. The 'LTSH' table (Linear ThreSHold) is a second, complementary method.

The LTSH table defines the point at which it is reasonable to assume linearly scaled advance widths on a glyph-by-glyph basis. This table should not be included unless bit 4 of the "flags" field in the 'head' table is set. The criteria for linear scaling is:

a. (ppem size is 50) AND (difference between the rounded linear width and the rounded instructed width � 2% of the rounded linear width)

or b. Linear width == Instructed width

The LTSH table records the ppem for each glyph at which the scaling becomes linear again, despite instructions effecting the advance width. It is a requirement that, at and above the recorded threshold size, the glyph remain linear in its scaling (i.e., not legal to set threshold at 55 ppem if glyph becomes nonlinear again at 90 ppem). The format for the table is:

Type	Name	Description
USHORT	version	Version number (starts at 0).
USHORT	numGlyphs	Number of glyphs (from "numGlyphs" in 'maxp' table).
BYTE	yPels[numGlyphs]	The vertical pel height at which the glyph can be assumed to scale linearly. On a per glyph basis.

Note that glyphs which do not have instructions on their sidebearings should have yPels = 1; i.e., always scales linearly.

Version:

$Revision: 6604 $

Author:

Michael Niedermair

Constructor Summary

TtfTableLTSH(XtfTableMap tablemap, XtfTableDirectory.Entry de, RandomAccessR rar)
Create a new object

Method Summary

int	getNumGlyphs() Returns the numGlyphs.
java.lang.String	getShortcut() Returns the table shortcut.
int	getType() Get the table type, as a table directory value.
int	getVersion() Returns the version.
byte[]	getYPels() Returns the yPels.
void	writeXML(XMLStreamWriter writer) Write the data to a XMLStreamWriter.

Methods inherited from class org.extex.font.format.xtf.tables.AbstractXtfTable

getGlyphName, getInitOrder, getTableMap, init, writeStartElement

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.extex.font.format.xtf.tables.XtfTable

getInitOrder, getTableMap, init

Constructor Detail

TtfTableLTSH

public TtfTableLTSH(XtfTableMap tablemap,
                    XtfTableDirectory.Entry de,
                    RandomAccessR rar)
             throws java.io.IOException

Create a new object

Parameters:

tablemap - the table map

de - entry

rar - input

Throws:

java.io.IOException - if an IO-error occurs

Method Detail

getNumGlyphs

public int getNumGlyphs()

Returns the numGlyphs.

Returns:

Returns the numGlyphs.

getShortcut

public java.lang.String getShortcut()

Returns the table shortcut.

Specified by:

getShortcut in interface XtfTable

Returns:

Returns the table shortcut.

See Also:

XtfTable.getShortcut()

getType

public int getType()

Get the table type, as a table directory value.

Specified by:

getType in interface XtfTable

Returns:

Returns the table type

getVersion

public int getVersion()

Returns the version.

Returns:

Returns the version.

getYPels

public byte[] getYPels()

Returns the yPels.

Returns:

Returns the yPels.

writeXML

public void writeXML(XMLStreamWriter writer)
              throws java.io.IOException

Write the data to a XMLStreamWriter.

Specified by:

writeXML in interface XMLWriterConvertible

Parameters:

writer - the XML-Writer

Throws:

java.io.IOException - if an IO-error occurs.

See Also:

XMLWriterConvertible.writeXML( org.extex.util.xml.XMLStreamWriter)