finally a auto-hinter module interface I'm satisfied with,
it's now time to change other font drivers to take advantage of it :-)
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David Turner
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@ -22,31 +22,115 @@
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#ifndef AUTOHINT_H
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#define AUTOHINT_H
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/***************************************************************************
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*
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* A small technical note regarding automatic hinting in order to clarify
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* this module interface.
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*
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* An automatic hinter might compute two kinds of data for a given face:
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*
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* - global hints: usually some metrics that describe global properties
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* of the face. It is computed by scanning more or less
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* agressively the glyphs in the face, and thus can be
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* very slow to compute (even if the size of global hints
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* is really small)
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*
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* - glyph hints: these describe some important features of the glyph
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* outline, as well as how to align them. They are generally
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* much faster to compute than global hints.
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*
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* The current FreeType auto-hinter does a pretty good job while performing
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* fast computations for both global and glyph hints. However, we might be
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* interested in introducing more complex and powerful algorithms in the
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* future, like the one described in the John D. Hobby paper, which
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* unfortunately require a lot more horsepower.
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*
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* Because a sufficiently sophisticated font management system would
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* typically implement a LRU cache of opened face objects to reduce memory
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* usage, it is a good idea to be able to avoid recomputing global hints
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* every time the same face is re-opened.
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*
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* We thus provide the ability to cache global hints outside of the face
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* object, in order to speed up font re-opening time. Of course, this
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* feature is purely optional, so most client programs won't even notice
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* it :o)
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*
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* I initially though that it'd be a good idea to cache the glyph hints too,
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* however, if my general idea now is that if you really need to cache these
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* too, you're simply in need of a new font format, where all this information
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* could be stored within the font file and decoded on the fly :-)
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*
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*/
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#include <freetype.h>
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typedef struct FT_AutoHinterRec_ *FT_AutoHinter;
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/***********************************************************************
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*
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* <FuncType>
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* FT_AutoHinter_Get_Global_Func
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*
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* <Description>
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* Retrieve the global hints computed for a given face object
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* the resulting data is dissociated from the face and will survive
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* a call to FT_Done_Face. It must be discarded through the API
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* FT_AutoHinter_Done_Global_Func.
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*
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* <Input>
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* hinter :: handle to source auto-hinter
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* face :: handle to source face object
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*
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* <Output>
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* global_hints :: typeless pointer to the global hints
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* global_len :: size in bytes of global hints
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*
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*/
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typedef void (*FT_AutoHinter_Get_Global_Func)( FT_AutoHinter hinter,
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FT_Face face,
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void* *global_hints,
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long *global_len );
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/***********************************************************************
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*
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* <FuncType>
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* FT_AutoHinter_Done_Global_Func
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*
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* <Description>
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* Discards the global hints retrieved through
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* FT_AutoHinter_Get_Global_Func. This is the only way these hints
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* are freed from memory.
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*
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* <Input>
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* hinter :: handle to auto-hinter module
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* global :: pointer to retrieved global hints to discard
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*/
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typedef void (*FT_AutoHinter_Done_Global_Func)( FT_AutoHinter hinter,
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void* global );
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/***********************************************************************
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*
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* <FuncType>
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* FT_AutoHinter_Init_Func
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*
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* <Description>
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* Each face can have its own auto-hinter object. This function
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* is used to initialise it. Its role is to perform a few statistics
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* on the face's content in order to compute global metrics like
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* blue zones and standard width/heights.
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* Compute or set the global hints for a given face object.
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*
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* <Input>
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* face :: handle to the face.
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* hinter :: handle to source auto-hinter module
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* face :: handle to target face object.
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* global_hints :: typeless pointer to global hints. If 0, the
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* hints are computed for the face
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*
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* <Note>
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* this function will call FT_Load_Glyph several times in order to
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* compute various statistics on the face's glyphs. This means that
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* the face handle must be valid when calling it.
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* it is up to client applications to ensure that the global hints
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* were retrieved for the same face object. Strange results may occur
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* otherwise..
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*
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* This function set the "hinter" and "hinter_len" fields of 'face'.
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*/
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typedef FT_Error (*FT_AutoHinter_Init_Func)( FT_Face face );
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typedef FT_Error (*FT_AutoHinter_Init_Func)( FT_AutoHinter hinter,
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FT_Face face,
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void* global_hints );
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/***********************************************************************
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*
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@ -54,19 +138,16 @@
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* FT_AutoHinter_Done_Func
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*
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* <Description>
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* Each face can have its own auto-hinter object. This function
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* is used to finalise and destroy it.
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* Discards the global hints for a given face..
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*
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* <Input>
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* face :: handle to the face.
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*
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* <Note>
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* This function clears the "hinter" and "hinter_len" fields of
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* "face". However, the face object is still valid and can be used
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* to load un-hinted glyphs..
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* hinter :: handle to source auto-hinter module
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* face :: handle to target face object.
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*
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*/
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typedef void (*FT_AutoHinter_Done_Func)( FT_Face face );
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typedef FT_Error (*FT_AutoHinter_Done_Func)( FT_AutoHinter hinter,
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FT_Face face );
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/***********************************************************************
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@ -93,7 +174,7 @@
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*/
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typedef FT_Error (*FT_AutoHinter_Load_Func)( FT_Face face,
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FT_UInt glyph_index,
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FT_ULong load_flags );
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FT_ULong load_flags );
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/***********************************************************************
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*
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@ -109,9 +190,11 @@
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FT_AutoHinter_Init_Func init_autohinter;
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FT_AutoHinter_Done_Func done_autohinter;
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FT_AutoHinter_Load_Func load_glyph;
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FT_AutoHinter_Get_Global_Func get_global_hints;
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FT_AutoHinter_Done_Global_Func done_global_hints;
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} FT_AutoHinter_Interface;
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#endif /* AUTOHINT_H */
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