Re: About combination of thai and devanagrari

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 <petercon_at_microsoft.com>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:* unicode-bounce_at_unicode.org [mailto:unicode-bounce_at_unicode.org] *On
> Behalf Of *li bo
> *Sent:* Wednesday, September 07, 2011 2:06 AM
> *To:* verdy_p_at_wanadoo.fr
> *Cc:* unicode_at_unicode.org
> *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 <verdy_p_at_wanadoo.fr> 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 <libo.imc_at_gmail.com>:****
>
> > 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!
> >****
>
> ** **
>
Received on Thu Sep 08 2011 - 05:45:24 CDT