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Major internal updates
Major internal updates
Thu, 22 Jun 2000 12:11:57 +0200
I've recently commited major internal updates to the library recently.
You'll find a summary below of what has changed. Note that the new code
isn't completely debugged (I suspect some problems in the drivers) so
do not consider it as "finished" as beta 7 was. Hopefully, this will
change soon.. The high-level API has changed a bit, but should not
break existing applications that uses the engine..
The changes came from basically two things:
- first, not all modules are font drivers, and the FT_Module
type was introduced. FT_Add_Driver, FT_Get_Driver, etc.. have
been replaced by FT_Add_Module, FT_Get_Module, etc.. and the
module API is now publicly available in <freetype/ftmodule.h>
- a new class of modules, called "renderers" are used to perform
various operations on native glyph image formats:
- transform them
- convert them to bitmaps
- get their bounding box
this is needed to truly support future glyph image formats (e.g.
bicolor glyphs, SVG glyphs, etc..) transparently. The old approach
didn't deal with transform and bboxes, and this could create a
additionally, FT_Get_Raster, FT_Set_Raster, etc.. have been replaced
by FT_Get_Renderer, FT_Set_Renderer, etc..
there is a new directory named "src/renderer" containing the
renderers corresponding to the "standard" and "smooth" rasters
As usual, any comments are appreciated, but I'll warn you when the move
- MAJOR INTERNAL REDESIGN:
A lot of internal modifications have been performed lately on the
source in order to provide the following enhancements:
- more generic module support:
The FT_Module type is now defined to represent a handle to a given
module. The file <freetype/ftmodule.h> contains the FT_Module_Class
definition, as well as the module-loading public API
The FT_Driver type is still defined, and still represents a pointer
to a font driver. Note that FT_Add_Driver is replaced by FT_Add_Module,
FT_Get_Driver by FT_Get_Module, etc..
- support for generic glyph image types:
The FT_Renderer type is a pointer to a module used to perform various
operations on glyph image.
Each renderer is capable of handling images in a single format
(e.g. ft_glyph_format_outline). Its functions are used to:
- transform an glyph image
- render a glyph image into a bitmap
- return the control box (dimensions) of a given glyph image
The scan converters "ftraster.c" and "ftgrays.c" have been moved
to the new directory "src/renderer", and are used to provide two
default renderer modules.
One corresponds to the "standard" scan-converter, the other to the
The current renderer can be set through the new function
The old raster-related function FT_Set_Raster, FT_Get_Raster and
FT_Set_Raster_Mode have now disappeared, in favor of the new:
see the file <freetype/ftrender.h> for more details..
These changes were necessary to properly support different scalable
formats in the future, like bi-color glyphs, etc..
- glyph loader object:
A new internal object, called a 'glyph loader' has been introduced
in the base layer. It is used by all scalable format font drivers
to load glyphs and composites.
This object has been created to reduce the code size of each driver,
as each one of them basically re-implemented its functionality.
See <freetype/internal/ftobjs.h> and the FT_GlyphLoader type for
- FT_GlyphSlot had new fields:
In order to support extended features (see below), the FT_GlyphSlot
structure has a few new fields:
linearHoriAdvance: this field gives the linearly scaled (i.e.
scaled but unhinted) advance width for the glyph,
expressed as a 16.16 fixed pixel value. This
is useful to perform WYSIWYG text.
linearVertAdvance: this field gives the linearly scaled advance
height for the glyph (relevant in vertical glyph
layouts only). This is useful to perform
Note that the two above field replace the removed "metrics2" field
in the glyph slot.
advance: this field is a vector that gives the transformed
advance for the glyph. By default, it corresponds
to the advance width, unless FT_LOAD_VERTICAL_LAYOUT
was specified when calling FT_Load_Glyph or FT_Load_Char
bitmap_left: this field gives the distance in integer pixels from
the current pen position to the left-most pixel of
a glyph image WHEN IT IS A BITMAP. It is only valid
when the "format" field is set to
"ft_glyph_format_bitmap", for example, after calling
the new function FT_Render_Glyph.
bitmap_top: this field gives the distance in integer pixels from
the current pen position (located on the baseline) to
the top-most pixel of the glyph image WHEN IT IS A
BITMAP. Positive values correspond to upwards Y.
loader: this is a new private field for the glyph slot. Client
applications should not touch it..
- support for transforms and direct rendering in FT_Load_Glyph:
Most of the functionality found in <freetype/ftglyph.h> has been
moved to the core library. Hence, the following:
- a transform can be specified for a face through FT_Set_Transform.
this transform is applied by FT_Load_Glyph to scalable glyph images
(i.e. NOT TO BITMAPS) before the function returns, unless the
bit flag FT_LOAD_IGNORE_TRANSFORM was set in the load flags..
- once a glyph image has been loaded, it can be directly converted to
a bitmap by using the new FT_Render_Glyph function. Note that this
function takes the glyph image from the glyph slot, and converts
it to a bitmap whose properties are returned in "face.glyph.bitmap",
"face.glyph.bitmap_left" and "face.glyph.bitmap_top". The original
native image might be lost after the conversion.
- when using the new bit flag FT_LOAD_RENDER, the FT_Load_Glyph
and FT_Load_Char functions will call FT_Render_Glyph automatically
- reformated all modules source code in order to get rid of the basic
data types redifinitions (i.e. "TT_Int" instead of "FT_Int", "T1_Fixed"
instead of "FT_Fixed"). Hence the format-specific prefixes like "TT_",
"T1_", "T2_" and "CID_" are only used for relevant structures..
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