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Document BBox and CBox computation problems for tricky fonts.

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This commit is contained in:
Werner Lemberg 2011-04-13 00:29:41 +02:00
parent 21b1a0de7c
commit b9baff23f4
4 changed files with 24 additions and 7 deletions
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5
include/freetype/freetype.h
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@ -4,8 +4,7 @@
/* */
/* FreeType high-level API and common types (specification only). */
/* */
/* Copyright 1996-2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, */
/* 2010 by */
/* Copyright 1996-2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@ -1058,7 +1057,7 @@ FT_BEGIN_HEADER
/* */
/* It is not possible to autohint such fonts using */
/* @FT_LOAD_FORCE_AUTOHINT; it will also ignore */
/* @FT_LOAD_NO_HINTING. You have to set both FT_LOAD_NO_HINTING */
/* @FT_LOAD_NO_HINTING. You have to set both @FT_LOAD_NO_HINTING */
/* and @FT_LOAD_NO_AUTOHINT to really disable hinting; however, you */
/* probably never want this except for demonstration purposes. */
/* */

10
include/freetype/ftbbox.h
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@ -4,7 +4,7 @@
/* */
/* FreeType exact bbox computation (specification). */
/* */
/* Copyright 1996-2001, 2003, 2007 by */
/* Copyright 1996-2001, 2003, 2007, 2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@ -73,6 +73,14 @@ FT_BEGIN_HEADER
/* <Return> */
/* FreeType error code. 0~means success. */
/* */
/* <Note> */
/* If the font is tricky and the glyph has been loaded with */
/* @FT_LOAD_NO_SCALE, the resulting BBox is meaningless. To get */
/* reasonable values for the BBox it is necessary to load the glyph */
/* at a large ppem value (so that the hinting instructions can */
/* properly shift and scale the subglyphs), then extracting the BBox */
/* which can be eventually converted back to font units. */
/* */
FT_EXPORT( FT_Error )
FT_Outline_Get_BBox( FT_Outline* outline,
FT_BBox *abbox );

9
include/freetype/ftglyph.h
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@ -4,7 +4,7 @@
/* */
/* FreeType convenience functions to handle glyphs (specification). */
/* */
/* Copyright 1996-2001, 2002, 2003, 2006, 2008, 2009 by */
/* Copyright 1996-2003, 2006, 2008, 2009, 2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@ -384,6 +384,13 @@ FT_BEGIN_HEADER
/* units in 26.6 pixel format. The value @FT_GLYPH_BBOX_SUBPIXELS */
/* is another name for this constant. */
/* */
/* If the font is tricky and the glyph has been loaded with */
/* @FT_LOAD_NO_SCALE, the resulting CBox is meaningless. To get */
/* reasonable values for the CBox it is necessary to load the glyph */
/* at a large ppem value (so that the hinting instructions can */
/* properly shift and scale the subglyphs), then extracting the CBox */
/* which can be eventually converted back to font units. */
/* */
/* Note that the maximum coordinates are exclusive, which means that */
/* one can compute the width and height of the glyph image (be it in */
/* integer or 26.6 pixels) as: */

7
include/freetype/ftoutln.h
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@ -5,7 +5,7 @@
/* Support for the FT_Outline type used to store glyph shapes of */
/* most scalable font formats (specification). */
/* */
/* Copyright 1996-2001, 2002, 2003, 2005, 2006, 2007, 2008, 2009, 2010 by */
/* Copyright 1996-2003, 2005-2011 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
@ -227,6 +227,9 @@ FT_BEGIN_HEADER
/* <Output> */
/* acbox :: The outline's control box. */
/* */
/* <Note> */
/* See @FT_Glyph_Get_CBox for a discussion of tricky fonts. */
/* */
FT_EXPORT( void )
FT_Outline_Get_CBox( const FT_Outline* outline,
FT_BBox *acbox );
@ -332,7 +335,7 @@ FT_BEGIN_HEADER
/* handled incorrectly. */
/* */
/* If you need `better' metrics values you should call */
/* @FT_Outline_Get_CBox ot @FT_Outline_Get_BBox. */
/* @FT_Outline_Get_CBox or @FT_Outline_Get_BBox. */
/* */
/* Example call: */
/* */