Mac OS X Porting - Native Fonts

Public Documentation License Notice

The contents of this Documentation are subject to the Public Documentation License Version 1.0 (the "License"); you may only use this Documentation if you comply with the terms of this License. A copy of the License is available at http://www.openoffice.org/licenses/PDL.html. The Original Documentation is "Fonts starting point and documentation". The Initial Writer of the Original Documentation is (JCA) Eric Bachard (C) 2006. All Rights Reserved. (Initial Writer contact(s): ericb@openoffice.org.)

Native fonts implementation

Introduction

Currently, OpenOffice.org on Mac OS X does not use directly Apple system fonts, but extracts .ttf part ot (most of) them, and uses X11 rendering to display them properly.

The pro to use X11 rendering is it is faster than use Apple font server, but the drawback is all featured improvement are not accessible, in particular kerning and hinting.

Note : Apple owns a Patent who does not allow us to use kerning and hinting as expected e.g. using Freetype 
( see :http://www.freetype.org/patents.html), so workaround or other hacks must be used.

First contact with Herbert Duerr (hdu), about fonts :

Choosen answers to start :

"...I already started an ATSUI port long ago. See issue 23283 for details (http://www.openoffice.org/issues/show_bug.cgi?id=23283). This patch is very old and worked for some simple situations..."

"..Everything is in VCL, especially the vcl/inc/sallayout.hxx header file is important. vcl/*/gdi/ subdirectories might be interesting too.

The SalLayout base class is the core of all VCL-text. It corresponds to an ATSUTextLayout object on ATSUI. All text display, measurements, text breaking, glyph fallback etc. are done via SalLayout objects.."

"..I think the best way is to deeply understand a SalLayout object is to get to know the very old VCL OutputDevice text related methods, and especially what the pDXArray parameter in them means. Then learn ATSUI, Uniscribe, ICU's layout engine and Java's TextLayout really well. A SalLayout is just the abstracted combination of all these layout engines. A SalLayout object has the "old pDXArray flavour" to keep the changes required by the rest of OOo minimal.."

"..Well, changing anything in the VCL text core is very hard, because it impacts basically everything text related in OOo. Since a simple change there can easily break some use cases, several scripts, platforms and may have a bad performance impact, I'd rather not change anything in the core...

"...If it is possible to isolate it to just the file salatslayout.cxx provided in issue 23283 then I'm all for it.."

Fixme : documentation starting point :

interesting documents about design of fonts implementations in OpenOffice.org  :

[FIXME]Verify if not obsolete Font management concept : http://gsl.openoffice.org/files/documents/16/1603/vcl_new_fontmanagement.pdf

window class hierarchy :

http://gsl.openoffice.org/files/documents/16/974/VCLClassHierarchyWindows.sxd

Little glossary

Impl prefix means "Implementation detail", and such variable, functions ...etc will only be visible locally

ATS : Apple Type Services. This server works if an only if a CFRunLoop( ) is running, and launched in main thread.

ATSUI : Apple Type Services for Unicode Imagery

Sal : System Abstraction Layer

Layout (for text layout) : Text Layout contains one ore more paragraphs of text together with style attributes that may apply to character,

lines or even the entire layout. The text layout contains informations about lines and layout attributes, including justification, rotation, etc

CarretPosition: Caret is the name for the symbol ^

Point: [FIXME]

Glyph: A Glyph represents the shape of a symbol. E.g. the glyph for the character "capital latin letter O" typically looks like a hollow ellipse.

Style: One of the three traditional design features of a typeface along with size and weight - styles are either regular, italic or condensed

Offset: in our context, a number indicating the distance (displacement) from the start of a data structure object and up to a given element

Boundary: A border that encloses a space or area

GIA: Glyph Information Attributes

Character style information: is contained in a style object associated ( not contained by ! ) a text layout object.

You can complete with the excellent glossary Herbert Duerr provided : http://gsl.openoffice.org/files/documents/16/1890/OOo_Glossary_Of_Font_Terms.htm

SalLayout base class description

[FIXME]

deprecated functions in Carbon API

ATSUCreateTextLayoutWithTextHandle  
ATSUSetTextHandleLocation   
ATSUSetFontFallbacks   
ATSUGetFontFallbacks  
ATSUFONDtoFontID  
ATSUFontIDtoFOND  
ATSUGetGlyphInfo  
ATSUDrawGlyphInfo  
ATSUIdle  

Content description : salatslayout.cxx

URL's & important LINKS

sallayout.hxx description

See : http://wiki.services.openoffice.org/wiki/Sallayout.hxx

Unicode references in Wikipedia

English reference : http://en.wikipedia.org/wiki/Unicode

French reference : http://fr.wikipedia.org/wiki/Unicode

ICU references in Wikipedia

English reference : http://en.wikipedia.org/wiki/International_Components_for_Unicode

French reference : http://fr.wikipedia.org/wiki/International_Components_for_Unicode

Apple documentation

ATS and ATSUI starting point : http://developer.apple.com/documentation/Carbon/Conceptual/ATS_Concepts/atsfonts_intro/chapter_1_section_1.html Apple's starting page leading to deeper docs: http://developer.apple.com/documentation/TextFonts/Typography-date.html

New Font Management

[FIXME]

See Herbert's Duerr document : http://www.openoffice.org/files/documents/16/1603/vcl_new_fontmanagement.pdf

This work is part of http://wiki.services.openoffice.org/wiki/Mac_OS_X_Porting_-_Work_Areas/Todo%27s

( Ericb 14:37, 21 May 2006 (CEST) )