Mac OS X Porting - Native Fonts

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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 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):

Native fonts implementation


Currently, 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 :, 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 ( 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  :

[FIXME]Verify if not obsolete Font management concept :

window class hierarchy :

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 Array

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 :

Work in progress

salatslayout.cxx License origin is justified here :]


What is important ? Reading , it was not easy to understand how was working UTF-8.

A character whose code point is below U+0080 is encoded with a single byte that contains its code point: these correspond exactly to the 128 characters of 7-bit ASCII. In other cases, up to four bytes are required. The most significant bit of these bytes is 1, to prevent confusion with 7-bit ASCII characters and therefore keep standard byte-oriented string processing safe.

Code range
Scalar value
128 codes
0zzzzzzz 0zzzzzzz ASCII equivalence range; byte begins with zero
seven z seven z
1920 codes
00000yyy yyzzzzzz 110yyyyy 10zzzzzz first byte begins with 110, the following byte begins with 10.
three y; two y, six z five y; six z
63488 codes
xxxxyyyy yyzzzzzz 1110xxxx 10yyyyyy 10zzzzzz first byte begins with 1110, the following bytes begin with 10.
four x,four y; two y,six z four x; six y; six z
1048576 codes
000wwwxx xxxxyyyy yyzzzzzz 11110www 10xxxxxx 10yyyyyy 10zzzzzz First byte begins with 11110, the following bytes begin with 10
three w, two x; four x, four y; two y, six z three w; six x; six y; six z

For example, the character aleph (א), which is Unicode U+05D0, is encoded into UTF-8 in this way:

  • It falls into the range of U+0080 to U+07FF. The table shows it will be encoded using two bytes, 110yyyyy 10zzzzzz.
  • Hexadecimal 0x05D0 is equivalent to binary 101-1101-0000.
  • The eleven bits are put in their order into the positions marked by "y"-s and "z"-s: 11010111 10010000.
  • The final result is the two bytes, more conveniently expressed as the two hexadecimal bytes 0xD7 0x90. That is the letter aleph (א) in UTF-8. side :

1) Headers

1.1) vcl/inc/salgdi.hxx, including definition of :
SalGraphics class 
1.2) vcl/inc/sallayout.hxx, including definitions of :
classes :
MultiSalLayout (inherits of SalLayout)

struct GlyphItem

1.3) vcl/aqua/inc/salgdi.h, including definitions of 
classes : 
ImplMacFontData (inherits of ImplFontData)

AquaSalGraphics (inherits of SalGraphics, does have ATSLayout as friend class)

2) Implementation

2.1) vcl/aqua/source/inc/salatslayout.cxx

Implements the classes :
ATSLayout (inherits of SalLayout)

existing ATSLayout methods are :
bool ATSLayout::LayoutText()
void ATSLayout::AdjustLayout()
void ATSLayout::DrawText()
int ATSLayout::GetNextGlyphs()
long ATSLayout::GetTextWidth()
long ATSLayout::FillDXArray()
int ATSLayout::GetTextBreak()
void ATSLayout::GetCaretPositions()
bool ATSLayout::GetBoundRect() 
bool ATSLayout::InitGIA()
Other class : PolyArgs, implementing :
void PolyArgs::Init()
void PolyArgs::AddPoint()
void PolyArgs::ClosePolygon()
OSStatus MyATSCubicMoveToCallback()
OSStatus MyATSCubicLineToCallback()
OSStatus MyATSCubicCurveToCallback()
OSStatus MyATSCubicClosePathCallback ()

Mac OS X API side:

Carbon API implementation (binding) is made in salatslayout.cxx

ATS and ATSUI starting point :

Apple's starting page leading to deeper docs:

Todo-list for native font implementation :

- missing methods (to be implemented) :
bool ATSLayout::GetGlyphOutlines()
ATSLayout::Simplify( )
- Fix known bugs :
   MultiLine does not work (writer cannot be used, because)
   Bad keyboard/charset ? (missig chars)
   When redrawing, everything is redrawn using the most little font size -> even the dialog boxes on menu bars
   Bad values returned 
- Implement MultiSalLayout
- Complete implementation   
- read Apple API [ Work in progress]
- describe current implementation : organisation / design [work in progress]
- design of new implementation [FIXME] find examples

Estimation of code remaining to write ~40 %

Done ( mainly Stephan Schaefer, with initial salatslayout.cxx file written by Herbert Duerr)


- adapt salatslayout.cxx to make it match with sallayout.hxx, and salgdi.hxx, saldata.hxx .etc 
to make it build with aquavlcl01, and do some tests :
- verify this server can be initialized inside (needs a CFRunLoop working to be correctly initialized )
- run it and fix instant crashs and verity there is no freeze


- fix compilations issues
- rewrite complete salatslayout.cxx
- verify salatsfontutils.cxx definition does match with new salatslayout.cxx content
- define correct naming convention
- replace old SalGraphicsData object implementation (found in pre-aquavcl01 files, and now obsolete, because we won't use QDraw anymore)
- understand current font implementation  ( using old salatslayout.cxx )  ( work in progress )
- analyse and describe Carbon binding in salatslayout.cxx [ 90% done]

Resources : use sample code to test/initialize ATS server ( using e.g. ATSUIDirectAccessDemo )

SalLayout base class description


salatslayout.cxx description

interesting functions in Carbon/ATSUI API


ATSCreateFontQueryRunLoopSource : Sets up your application to handle font queries

CFRunLoopSourceRef ATSCreateFontQueryRunLoopSource (
  CFIndex queryOrder,
  CFIndex sourceOrder,
  ATSFontQueryCallback callout,
  const ATSFontQuerySourceContext * context,

More Infos on CFRunLoopSourceRef



Contains the coordinates needed to draw a caret.

struct ATSUCaret {
  Fixed fX; 
  Fixed fY; 
  Fixed fDeltaX; 
  Fixed fDeltaY;

More infos on ATSUCaret

MultiSalLayout implementation

Original code is in vcl/source/gdi/sallayout.cxx

// =======================================================================

MultiSalLayout::MultiSalLayout( SalLayout& rBaseLayout )   // Ctor 

// -----------------------------------------------------------------------

MultiSalLayout::~MultiSalLayout()   // Dtor
// -----------------------------------------------------------------------

[FIXME] describe

bool MultiSalLayout::AddFallback( SalLayout& rFallback,
    ImplLayoutRuns& rFallbackRuns, ImplFontData* pFallbackFont )
// -----------------------------------------------------------------------

[FIXME] describe

bool MultiSalLayout::LayoutText( ImplLayoutArgs& rArgs )


// -----------------------------------------------------------------------

[FIXME] describe

void MultiSalLayout::AdjustLayout( ImplLayoutArgs& rArgs )

// -----------------------------------------------------------------------

[FIXME] describe

void MultiSalLayout::InitFont() const

// -----------------------------------------------------------------------

[FIXME] describe

void MultiSalLayout::DrawText( SalGraphics& rGraphics ) const

 // -----------------------------------------------------------------------

[FIXME] describe

int MultiSalLayout::GetTextBreak( long nMaxWidth, long nCharExtra, int nFactor ) const

// -----------------------------------------------------------------------

[FIXME] describe

long MultiSalLayout::FillDXArray( sal_Int32* pCharWidths ) const

// -----------------------------------------------------------------------

[FIXME] describe

void MultiSalLayout::GetCaretPositions( int nMaxIndex, sal_Int32* pCaretXArray ) const

// -----------------------------------------------------------------------

[FIXME] describe

int MultiSalLayout::GetNextGlyphs( int nLen, sal_Int32* pGlyphIdxAry, Point& rPos,
    int& nStart, sal_Int32* pGlyphAdvAry, int* pCharPosAry ) const

// -----------------------------------------------------------------------

[FIXME] describe

bool MultiSalLayout::GetOutline( SalGraphics& rGraphics,
    ::basegfx::B2DPolyPolygonVector& rPPV ) const

// -----------------------------------------------------------------------

[FIXME] describe

bool MultiSalLayout::GetBoundRect( SalGraphics& rGraphics, Rectangle& rRect ) const

// =======================================================================

deprecated functions in Carbon API

ATSUGetGlyphInfo  [done]

Content description : salatslayout.cxx

URL's & important LINKS

sallayout.hxx description

See :

Unicode references in Wikipedia

English reference :

French reference :

Note: prefer english reference, more complete

Unicode references

Bidirectionnal Algorithms :

UTF-8 and Unicode FAQ

ICU references in Wikipedia

English reference :

French reference :

Apple documentation

ATS and ATSUI starting point : Apple's starting page leading to deeper docs:

New Font Management


See Herbert's Duerr document :

Other ATSUI implementations

The Cairo library has an implementation of ATSUI font rendering, it can be studied for, because it is licensed with LGPL. See the code here:;a=blob;hb=HEAD;f=src/cairo-atsui-font.c

Mac OS X port on the wiki

  1. Build Aqua version of
  2. Pierre de Filippis Wiki
  3. Christian Lippka wiki :
  4. Mac OS X port Meetings :

This work is part of

Ericb 10:36, 3 September 2006 (CEST)