Thanks for your great help. Does it mean if i want to support Devanagari scripts by using truetype font, following must be done. 1. A higher-level layout engine like Pango to layout the text. 2. As truetype font can be considered as a kind of Opentype font, OpenType Layout tables（GSUB, GPOS）can be used to handle Devanagari scripts.
Libo On Wed, Sep 7, 2011 at 10:41 PM, Peter Constable <[email protected]>wrote: > “TrueType” can mean different things depending on context. **** > > ** ** > > **- **The TrueType font format specification**** > > **- **The TrueType glyph outline/ hinting format**** > > **- **The “sfnt” font file format**** > > ** ** > > These are all inter-related. The TrueType font format was defined around 20 > years ago by Apple. Two aspects of that format are (1) an overall file > structure, often referred to as the “sfnt” format, and (2) a particular way > of describing glyph outlines and hinting.**** > > ** ** > > One particular thing to note regarding the sfnt container format is that it > involves a set of data tables and a table directory which are inherently > extensible. The TrueType font format defined a particular set of tables, but > a font could include additional tables and still be considered a TrueType > font.**** > > ** ** > > The OpenType format builds on the TrueType format but leverages the > extensibility of the sfnt format in three particular ways:**** > > ** ** > > **- **It defines additional tables, known collectively as > OpenType Layout tables (GDEF, GSUB, GPOS, JSTF and BASE), that provide > functionality needed for complex scripts and fine typography**** > > **- **It defines an additional table, DSIG, to support digital > signing of font files**** > > **- **It allows for glyph outline data using Adobe’s CFF format > (the outline format used in Type 1)**** > > ** ** > > In principle, any OpenType font that includes glyph data in TrueType format > can be considered a TrueType font. (If it includes CFF outlines, not > TrueType outlines, then it is not a valid TrueType font.) Likewise, any font > that conforms to the TrueType spec is, in principle, also an OpenType font. > But to avoid confusion it’s best to use these terms in a distinctive way: if > a font has one or more of the three additional types of data (OTL tables, > DSIG tables, CFF outlines), then it’s best to refer to that as an “OpenType” > font and not a “TrueType font”. **** > > ** ** > > To support Thai or Devanagari, software that has some higher-level layout > engine is required. OpenType Layout tables require rendering engines that > know how to interact with the data in those tables. There are other > sfnt-based font formats that use different data tables for complex-script > support; in particular, Graphite and AAT. Each of those require > corresponding layout engines.**** > > ** ** > > ** ** > > Hope that helps.**** > > peter**** > > ** ** > > ** ** > > *From:* [email protected] [mailto:[email protected]] *On > Behalf Of *li bo > *Sent:* Wednesday, September 07, 2011 2:06 AM > *To:* [email protected] > *Cc:* [email protected] > *Subject:* Re: About combination of thai and devanagrari**** > > ** ** > > If I use truetype font, Does it mean i need a higher-level layout engine to > layout the font?**** > > I know that there are OpenType tables (GPOS and GSUB) to handle the shape > and combine for complex scripts.**** > > But Is the OpenType tables support truetype font? I even don't know the > difference between the truetype font and opentype font.**** > > Thanks!**** > > **** > > > > **** > > On Tue, Sep 6, 2011 at 1:53 PM, Philippe Verdy <[email protected]> wrote: > **** > > Devanagari, not Decanagrari I suppose... Starts by looking at the > TrueType and OpenType specifications: > http://www.microsoft.com/typography/SpecificationsOverview.mspx > Then look at the details of the OpenType features needed for > Devanagari and Thai. > > You'll immediately see that Thai is much less complex than Devanagari > to implement. > > There are other competing technologies, base on TrueType (AAT for > MacOS, Graphite portable across platforms, but not very well supported > in applications). > > SVG fonts for now cannot support these scripts very well due to the > impossibility to map precisely the contextual forms that are unified > in Unicode (for Thai, well it could work with modern texts, but for > Devanagari, it's impossible without additional data for mapping the > contextual glyphs): there's still no specification in SVG fonts for > "features" like in OpenType, AAT and Graphite. In addition, the DOM > API for SVG fonts is not accessible in a documented way (only "opaque" > interfaces are available; you have to rely to the XML DOM instead). > > There are tricks to support Devanagari with Type1 fonts, but this > requires integratinf additional Postscript routines, specific to the > PostScript engine, to keep context variables in some accessible global > directory, such as the device context, normally not made for that, or > by self modifying the font's directory (such trick is used to generate > some Barcode fonts; font tools generally provide no help to integrate > those routines). > > But you may want to create a composite font, in which case a SVG font > can be built that combines two existing OpenType fonts (without > modifying them and without importing or converting their glyph > definitions), grouped under a single family-name and usable on the web > for CSS. Of you can do that with CSS "@font{ ...}", for later use of > the new family in a stylesheet or in HTML. > > -- Philippe -- > > 2011/9/6 li bo <[email protected]>:**** > > > I'd like to implement the combination of thai and decanagrari scripts > using > > vector font. But I have no idea about it. How do i adjust the position > of > > the combined glyph? Could anyone give some advices or references? Thanks > a > > lot! > >**** > > ** ** >
