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freetype/docs/apiref.txt
mnerv 5edbb7a80a FreeType 1.31.1
2023-08-27 18:03:45 +02:00

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The FreeType Engine
Core Library Reference
-----------------------------------
Table of Contents:
Introduction
I. Types
II. Functions
III. Error codes
--------------------
Introduction
============
This reference presents the types, functions, and error codes
defined in the high-level API header file `freetype.h'. Note that
all symbols defined in this file are prefixed by `TT_', to avoid
name conflicts with other packages at link time.
The reference for extensions of the FreeType library can be found
in the file apirefx.txt.
--------------------------------------------------------------------
--------------------------------------------------------------------
I. Types
========
Here is the list of all the types defined in the core FreeType
API. Their exact definition can be found in the file `freetype.h'
which should be included by every client application.
TT_Bool
Can be either non-zero (true) or zero (false).
..................................................................
TT_Fixed
A signed 16.16 fixed float integer type used to specify
transform coefficients and other important data.
..................................................................
TT_FWord
A signed 16-bit type used to express a distance measured in the
font's original EM units. These are also called `FUnits' in the
TrueType specification.
..................................................................
TT_UFWord
An unsigned 16-bit type.
..................................................................
TT_String
TT_Char
TT_Byte
These types represent various 8-bit integer values (for strings,
signed, and unsigned values, respectively).
..................................................................
TT_Short
TT_UShort
TT_Long
TT_ULong
These four types are aliases for 16-bit integer (signed and
unsigned) and 32-bit integer types (signed and unsigned).
..................................................................
TT_F2Dot14
A 2.14 fixed float integer type used for unary vectors and some
scaling coefficients. Its layout is:
s : 1 -- sign bit
m : 1 -- mantissa bit
f : 14 -- unsigned fractional value
where `s:m' is the 2-bit signed integer value to which the
always positive fractional part `f' should be added.
..................................................................
TT_F26Dot6
A 26.6 fixed float integer format used to define fractional
pixel coordinates. Here, 1 unit = 1/64 pixel.
..................................................................
TT_Pos
This type is used to store point coordinates, either in
fractional pixels (26.6 fixed floats) or in EM units (simple
integers).
The meaning of the value depends on the context. For example,
all distances relative to a scaled glyph are expressed in
fractional pixels (including bearings, advances, etc). However,
the same distances are in notional font units when the glyph was
loaded unscaled.
..................................................................
TT_UnitVector
A simple structure used to store a unit vector. The vector's
coordinates are expressed in fixed float format (2.14).
struct
{
TT_F2Dot14 x;
TT_F2Dot14 y;
}
..................................................................
TT_Vector
A simple structure used to store a single vector. Its
coordinates are expressed in fixed float format (26.6).
struct
{
TT_F26Dot6 x;
TT_F26Dot6 y;
}
..................................................................
TT_Matrix
A simple structure used to store a single 2x2 matrix. Its
coefficients are expressed in 16.16 fixed float format. This
matrix is used to perform linear transformations on the glyph
outline, such as slanting or rotation.
struct
{
TT_Fixed xx, xy;
TT_Fixed yx, yy;
};
The computation performed is:
x' = xx * x + xy * y
y' = yx * x + yy * y
..................................................................
TT_BBox
A simple type to hold a glyph's bounding box. Used by the
TT_Get_Outline_BBox() API.
struct
{
TT_Pos xMin, yMin;
TT_Pos xMax, yMax;
}
..................................................................
TT_Outline
Outlines are now full-class citizens, with their own API.
This structure is used to describe a vectorial glyph
representation to the rasterizer. It is made of several fields
described below. Note however that:
***** THIS STRUCTURE MAY CHANGE IN THE FUTURE. We thus
***** encourage you to use the outlines APIs described below to
***** process your outlines, i.e., create/copy/translate/
***** transform them as well as rendering bitmaps and pixmaps.
***** THE STRUCTURE CHANGED BETWEEN 1.0 and 1.1!
Now that you have been warned, the fields are:
- An array of points:
The `n_points' field gives the number of points in the
outline, while their coordinates are found in the single
vector array `points'. The `flag' array holds for each point
a flag indicating its type.
Currently, only the first bit (bit 0, the least significant
bit) of each byte is meaningful to the rasterizer. If set, it
indicates that the point is _on_ the curve. If not set, the
point is said to be _off_ the curve. It is then a Bezier
control point.
For more information about point states, read the TrueType
specification or the scan-line documentation `raster.txt'.
- An array of contours' end-point indexes:
The `n_contours' field gives the number of contours, while the
`contours' array holds the indexes of each contour's last
point. Note that the first contour always begin at point 0.
Hence, contours[0] holds the index of the last point of the
first contour. The second contour starting at point number
`contours[0]+1' and ending a point number `contours[1]'.
** IMPORTANT NOTE: **
*********************
The last table entry _must_ always give the total number of
points used to draw the contours, i.e.:
contours[n_contours - 1] == n_points
If this value is bigger than `n_points' when calling the
scan-line converter, the component will immediately return
an error (TT_Err_Too_Many_Points). If the value is smaller,
only the points contained in the described contours will be
used in the conversion process.
- An owner field:
This flag should **NEVER** be changed by the user. It
indicates whether the pointer fields own the arrays they refer
to (when the flag is set), or if they simply alias them (flag
unset).
- A high precision flag:
If this boolean is set (i.e. not zero), the scan-line
converter uses a higher precision to compute segment and
Bezier coordinates (more precisely, it uses 1/1024 precision,
instead of the normal 1/64). This is of course slower but can
be important for glyphs rendered at small sizes.
- A second pass flag:
If this boolean is set, the scan-line converter performs a
second sweep on the bitmap/pixmap to detect vertical drop-out.
Only horizontal drop-outs are detected in the first pass.
This is slower, but important for glyphs rendered at small
sizes.
- A dropout mode:
Used to specify the method to apply for drop-out control (also
called `continuity testing' in other environments). The mode
value must be one of the values defined by the TrueType
specification.
The recent modes 4 and 5 introduced in the newest TrueType
specification (Version 1.66) are fully supported.
An invalid value (i.e., not 0, 1, 2, 4, or 5) is taken as no
dropout control (equivalent to mode 0).
NOTE 1:
The outline returned by TT_Get_Glyph_Outline() only alias the
data that is part of a glyph container (see below). However,
it is possible to create and process your own outlines with
the new API functions TT_New_Outline(), TT_Done_Outline(),
TT_Copy_Outline(), TT_Translate_Outline(), etc.
TT_Done_Outline() will only discard an outline's array if it
owns them.
NOTE 2:
The outlines created by TT_New_Outline() are _not_ released by
the engine on TT_Done_FreeType(), they must be discarded
explicitly by the user who has created them!
NOTE 3:
The glyph loader sets the fields `high_precision',
`dropout_mode' and `second_pass' automatically.
NOTE 4:
This structure was called TT_Glyph_Outline in beta versions of
FreeType.
..................................................................
TT_Glyph_Metrics
A structure used to return simple glyph metrics, usable for
either horizontal or vertical layout. The values are expressed
in fractional pixels (26.6 format) if scaling was active, and in
FUnits otherwise.
The main idea was to accomodate vertical text layouts by getting
rid of the two explicit `leftSideBearing' and `advanceWidth'
names.
The meaning of the fields varies with the text layout:
bearingX: Also known as the `left side bearing'. For
horizontal metrics, this value gives the horizontal
distance from the pen position to the glyph's bbox
xmin, otherwise it specifies the vertical distance.
bearingY: Also known as the `top side bearing', this is the
vertical distance from the baseline to the glyph's
bbox ymax for horizontal metrics, the horizontal
distance otherwise.
struct
{
TT_BBox bbox; /* the glyph's bbox */
TT_Pos bearingX; /* left-side bearing */
TT_Pos bearingY; /* top-side bearing */
TT_Pos advance; /* advance width or height */
};
** IMPORTANT NOTE **
Because of the convention used by the TrueType engine, the
outlines generated at glyph-load time are all placed so that
the pen is at position (0,0). This means that you don't need
to increase the pen position by `bearingX' and/or `bearingY'
before writing a glyph. Text output can be performed with
simple lines like:
for (glyphs in text)
{
TT_Load_Glyph( ... );
TT_Get_Glyph_Outline( glyph, &outline );
TT_Translate_Outline( outline,
cur_pos_x * 64, cur_pos_y * 64 );
TT_Get_Outline_Bitmap( outline, bitmap );
/* blit bitmap to surface */
cur_pos_x += (metrics.advance + 32) / 64
}
See the file `test/ftstring.c' for an example.
NOTE 2:
This structure has changed from the beta version of FreeType.
NOTE 3:
FreeType implements only TT_Get_Glyph_Metrics() to return
horizontal metrics. For extracting vertical metrics you
should use TT_Get_Glyph_Big_Metrics().
..................................................................
TT_Big_Glyph_Metrics
This structure is used to return the metrics of a glyph for both
horizontal and vertical layout.
The `linearXXX' fields represent unhinted scaled metrics values.
They can be useful for applications which need to compute device
independent placement of glyphs. Applying these metrics to
hinted glyphs will in most cases ruin the grid fitting performed
by the bytecode interpreter.
struct
{
TT_BBox bbox; /* the glyph's bounding box */
TT_Pos horiBearingX; /* horizontal left-side bearing */
TT_Pos horiBearingY; /* horizontal top-side bearing */
TT_Pos vertBearingX; /* vertical left-side bearing */
TT_Pos vertBearingY; /* vertical top-side bearing */
TT_Pos horiAdvance; /* horizontal advance */
TT_Pos vertAdvance; /* vertical advance */
TT_Pos linearHoriBearingX; /* lin. scaled hor. lsb. */
TT_Pos linearHoriAdvance; /* lin. scaled hor. adv. */
TT_Pos linearVertBearingY; /* lin. scaled vert. tsb. */
TT_Pos linearVertAdvance; /* lin. scaled vert. adv. */
}
..................................................................
TT_Instance_Metrics
A structure used to return instance (point size) metrics.
struct
{
int pointSize;
/* point size in points (1 point = 1/72 inch) */
TT_UShort x_ppem; /* horizontal pixels per EM square */
TT_UShort y_ppem; /* vertical pixels per EM square */
TT_Fixed x_scale; /* 16.16 scale for EM -> frac pixels */
TT_Fixed y_scale; /* 16.16 scale for EM -> frac pixels */
TT_UShort x_resolution; /* device hor. res. in dpi */
TT_UShort y_resolution; /* device vert. res. in dpi */
};
The fields `x_scale' and `y_scale' can be used by clients to
convert from notional units (in funits) to fractional
pixels (in 26.6 fixed float format), e.g.:
TT_FUnit em_distance;
TT_F26Dot6 frac_distance;
TT_Fixed x_scale;
frac_distance = (em_distance * x_scale) / 0x10000;
..................................................................
TT_Raster_Map
This structure is used to describe a target bitmap (or pixmap)
to the scan-line converter. It _must_ be set up by the client
application.
- The `rows' field contains the total number of rows in the
bitmap.
- The `width' field gives the number of pixels per row (a bit or
a byte, depending on the map's nature).
- The `cols' field gives the number of columns, i.e. bytes,
taken by each row in the map buffer.
** IMPORTANT: ** The `cols' field must be a multiple of 4 for
pixmaps!
Typically, its value should be `(width+7)/8' for bitmaps, and
`(width+3) & -4' for pixmaps.
- The `flow' field gives the map's vertical orientation.
If the first bytes of the bitmap buffer pertain to its upper
row, the flow is said to be going `down', and the field should
take the value `TT_Flow_Down'. If these bytes pertain to its
lowest row, the flow is going `up', and the value is
`TT_Flow_Up'.
As an example, the PC video modes use a `down' flow, where the
first VRAM byte corresponds to the upper and leftmost corner
of the screen.
- The `bitmap' field is a typeless pointer to the map's buffer.
- The `size' field contains the buffer's size in bytes. It is
usually computed as follows:
size = rows * cols;
NOTE 1:
For bitmaps, the leftmost-pixel is related to the highest
(i.e. most significant) bit of its byte. There is currently
no support for the opposite convention found in some systems.
(It can be easily added if you really need it, just ask the
development team.)
struct
{
int rows; /* number of rows */
int cols; /* number of columns (bytes) per row */
int width; /* number of pixels per line */
int flow; /* bitmap orientation */
void* bitmap; /* bit/pixmap buffer */
long size; /* bit/pixmap size in bytes */
} TT_Raster_Map;
NOTE 2:
TT_Get_Outline_Bitmap() resp. TT_Get_Glyph_Bitmap() are used
to render bitmaps into a TT_Raster_Map. The convention used
is 0 for the background, and 1 for the foreground. The glyph
is simply `or-ed' to the bitmap buffer.
NOTE 3:
TT_Get_Outline_Pixmap() and TT_Get_Glyph_Pixmap() are used to
render pixmaps into a TT_Raster_Map. Note that pixels are
drawn in spans of 4 successive bytes, only if needed. This
means that you must ALWAYS pass a clean pixmap buffer to these
functions. Otherwise, garbage could accumulate!
..................................................................
TT_Header
This structure is used to hold the font's header. Its layout
and meaning are defined in the TrueType specification, in the
`head' section.
..................................................................
TT_Horizontal_Header
This structure is used to hold the font's horizontal header.
Its layout and meaning are defined in the TrueType
specification, in the `hhead' section.
..................................................................
TT_OS2
This structure is used to hold the font's OS/2 table. Its
layout and meaning are defined in the TrueType specification, in
the `OS/2' section.
Note that since FreeType 1.3, we support fonts without an OS/2
table (mainly old but popular Mac fonts). In this case, the
table's `version' field will be set to 0xFFFF by the loader, and
all other fields will be zeroed.
..................................................................
TT_Postscript
This structure is used to hold the font's PostScript table. Its
layout and meaning are defined in the TrueType specification, in
the `post' section.
..................................................................
TT_Face_Properties
This structure is used to return an opened face's properties.
These are:
- The total number of glyphs in the font, given by the field
`num_Glyphs'.
- The maximum number of points for the font's glyphs. This
value is used to allocate the points tables of a glyph
container's outline. It can be fairly large (like 256 points
for Roman fonts).
- The maximum number of contours for the font's glyphs. This
value is used to allocate the contours tables of a glyph
container's outline. It can be fairly large (over 16, even in
Roman fonts).
- The number of character mappings and name records within the
font. These values can still be retrieved through the APIs
TT_Get_CharMapCount() and TT_Get_Num_Names(), though these
have been _seriously_ deprecated.
- The number of associated faces. This number is always 1 for a
normal TrueType font file. However, when the face object was
opened from a TrueType collection, it contains the total
number of embedded fonts.
- Pointers to the face's header, horizontal header, OS/2, and
PostScript tables.
struct
{
TT_UShort num_Glyphs; /* number of glyphs in face */
TT_UShort max_Points; /* max. numb. of points in a glyph */
TT_Short max_Contours;
/* maximum number of contours in a glyph */
TT_ULong num_Faces;
/* 1 for normal TrueType files resp. */
/* the number of embedded faces for TT */
/* collections */
TT_Header* header; /* TrueType header table */
TT_Horizontal_Header* horizontal;
/* TrueType horizontal header */
TT_Vertical_Header* vertical;
/* TrueType vertical header */
TT_OS2* os2; /* TrueType OS/2 table */
TT_Postscript* postscript;
/* TrueType PostScript table */
} TT_Face_Properties;
- Note that the `vertical' field is set to NULL if the font file
does not contain any vertical metrics.
- Note also that since version 1.3 we support font files without
an OS/2 table. See the definition of TT_OS2 for more details.
..................................................................
TT_Stream
This handle type defines a stream used to access a font file's
data. A client application should never deal with streams
directly, but some engine extensions need it to support more
advanced features like sbit support.
..................................................................
TT_Face
This type defines a handle used to reference a face object. The
objects are never accessed directly by a client application; it
can only obtain handles to new objects, and use them to query
specific information or processes.
See also:
TT_Open_Face(), TT_Open_Collection(), TT_Close_Face(),
TT_Get_Face_Properties(), etc.
..................................................................
TT_Instance
This type defines a handle used to reference an instance object
(also called a `pointsize' in other type engines). An instance
is always created from a valid face object, and is destroyed
with it by the engine.
See also:
TT_New_Instance(), TT_Close_Instance(),
TT_Set_Instance_Pointsize(), TT_Set_Instance_Resolutions(),
etc.
..................................................................
TT_Glyph
This type defines a handle used to reference a glyph container
object. A glyph container is an object owning tables sized to
the font's maximum profile to hold any glyph of a given font
file.
It contains an outline, some metrics, as well as some data
related to the way it should be processed by the scan-line
converter.
Note that a glyph container doesn't contain any bitmap or
pixmap!
See also:
TT_New_Glyph(), TT_Close_Glyph(), TT_Get_Glyph_Metrics(),
TT_Get_Glyph_Big_Metrics(), TT_New_Outline(),
TT_Get_Glyph_Outline(), TT_Get_Glyph_Bitmap(),
TT_Get_Glyph_Pixmap()
..................................................................
TT_Error
This is the type of all error codes returned by the API. Nearly
all functions return an error code, set to 0 in case of success.
A list of all error codes is given in section III.
..................................................................
TT_Engine
For the sake of re-entrancy it is possible to distinguish
`engines' to separate several running instances of the library.
For example, it could be used as a DLL shared by several client
applications.
Each client program must begin by creating its own engine,
through a call to TT_Init_FreeType(). The engine must also be
passed as the first argument of the following functions:
TT_Open_Face()
TT_Open_Collection()
TT_Set_Raster_Gray_Palette()
TT_Get_Outline_Bitmap()
TT_Get_Outline_Pixmap()
TT_Done_FreeType()
Note that any FreeType object pertains to one single engine
(there is no sharing). Closing an engine with
TT_Done_FreeType() will delete all the objects that have been
allocated within its instance.
--------------------------------------------------------------------
--------------------------------------------------------------------
II. Functions
=============
Here is a list of the core library's API.
NOTE:
A function's default result is an error code of type TT_Error; a
list of error codes is given in section III below.
Some functions return other types, in which case the result type
is documented with its description.
..................................................................
TT_FreeType_Version( int* major, int* minor );
Queries the major and minor version of the library.
..................................................................
TT_Init_FreeType( TT_Engine* engine );
Creates and initializes a new engine. Returns a handle to the
engine in the `*engine' variable.
This call must be performed before any other function of
FreeType is invoked. The engine handle must be passed to the
following functions:
TT_Open_Face()
TT_Open_Collection()
TT_Set_Raster_Gray_Palette()
TT_Done_FreeType()
..................................................................
TT_Done_FreeType( TT_Engine engine );
Finalizes and destroys an engine. This call destroys _all_
objects that were previously created and used with the engine.
..................................................................
TT_Open_Face( TT_Engine engine,
TT_Text* fontPathName,
TT_face* face );
This call opens a font file, located by `fontPathName', and
returns a handle to the newly corresponding face object in the
handle `*face'. The object is part of the `engine' instance.
Example:
error = TT_Open_Face( engine, "c:\ttf\wingding.ttf", &face );
if ( error )
fprintf( stderr, "Could not open face.\n" );
NOTE 1:
The font file can be a TrueType collection; in this case, the
engine will always open the first embedded font found in the
file.
NOTE 2:
`TT_Text' is usually defined as `char' by a typedef
declaration. It may be a 16-bit quantity (or even wider) for
some operating systems; see ttconfig.h for details.
..................................................................
TT_Open_Collection( TT_Engine engine,
TT_Text* collectionPathName,
TT_ULong fontIndex,
TT_Face* face );
This call opens one of the fonts found in a TrueType collection.
The font is selected through the `fontIndex' argument. The
first font has index 0.
Note that to know a collection's number of embedded fonts,
you will have to:
1 - open the first collection font with TT_Open_Face().
2 - query the face's properties through
TT_Get_Face_Properties().
The number of embedded faces is then `properties->num_Faces'.
Example:
TT_Face face;
TT_Face_Properties properties;
/* Open first embedded collection font */
error = TT_Open_Face( engine, "c:\ttf\sample.ttc", &face );
if ( error ) { ...error... }
/* Get face properties */
error = TT_Get_Face_Properties( face, &properties );
if ( error ) { ...error... }
printf( "There are %d fonts in this collection.\n",
properties->num_Faces );
TT_Close_Face( face );
/* Open second font in collection */
error = TT_Open_Collection( engine, "c:\ttf\sample.ttc", 1,
&face );
if ( error ) { ...error... }
NOTE 1:
If the file isn't a collection, `fontIndex' must be zero.
Otherwise, an error will be returned.
NOTE 2:
`TT_Text' is usually defined as `char' by a typedef
declaration. It may be a 16-bit quantity (or even wider) for
some operating systems; see ttconfig.h for details.
..................................................................
TT_Set_Raster_Gray_Palette( TT_Engine engine,
TT_Byte* palette );
Sets the gray-level palette for an engine. The palette is used
to create pixmaps through the TT_Get_Glyph_Pixmap() function.
It is an array of five bytes, following the convention:
palette[0] = background (white)
palette[1] = light
palette[2] = medium
palette[3] = dark
palette[4] = foreground (black)
..................................................................
TT_Get_Face_Properties( TT_Face face,
TT_Face_Properties* properties );
Returns the `face' object's `*properties'. This structure
contains various data like the total number of glyphs and
pointers to some mandatory TrueType tables.
See the definition of TT_Face_Properties in section I for more
details.
Note that since version 1.3, FreeType supports fonts with no
OS/2 table, like many old Mac fonts. See the definition of
TT_OS2 for more details.
..................................................................
TT_Get_Face_Metrics( TT_Face face,
TT_UShort firstGlyph,
TT_UShort lastGlyph,
TT_Short* leftBearings,
TT_UShort* widths,
TT_Short* topBearings,
TT_UShort* heights );
This function returns the original horizontal AND vertical
metrics for a given face `face' and a given glyph range specified
by `firstGlyph' and `lastGlyph' as found in the `hmtx' and `vmtx'
tables. These are the glyphs' left-side bearings (in
`leftBearings') and horizontal advance widths (in `widths'), as
well as top-side bearings (in `topBearings') and vertical advance
heights (in `heights'). If you aren't interested in any of the
metrics fields, simply set its value to NULL.
All are expressed in font units, a.k.a. EM units.
The metrics arrays must be allocated by the client program.
IMPORTANT NOTE:
As vertical metrics are optional in a TrueType font, this
function will return an error (TT_Err_No_Vertical_Data) if this
function is called on such a face with non-NULL `topBearings'
or `heights' arguments.
If a font has no vertical data, the `vertical' field in its
properties structure is set to NULL.
..................................................................
TT_Set_Face_Pointer( TT_Face face,
void* data );
For convenience purposes, each face object has a `generic'
pointer which value is unused by the engine, but that can be set
freely by client applications through this function.
Do what you want with it; it is here to give you a chance to
link a face object to your own structures and data.
..................................................................
void* TT_Get_Face_Pointer( TT_Face face );
^^^^
Returns a face object's generic pointer. See
TT_Set_Face_Pointer() above.
..................................................................
TT_Flush_Face( TT_Face face );
Closes a given face object's file handler or descriptor. This
is useful to save system resources if your application opens
dozens or even hundreds of fonts. The face object is still
valid, and its file will be re-opened automatically on the next
request which requires disk access.
..................................................................
TT_Close_Face( TT_Face face );
Closes a given `face' object. This function will also destroy
all the face's child instances. The face's glyphs will not be
destroyed, however.
..................................................................
TT_New_Instance( TT_Face face,
TT_Instance* instance );
Creates a new instance object related to the `face' object. A
handle to the newly created instance is returned in `instance'.
The default instance resolution is 96dpi in both vertical and
horizontal direction; the default point size is 10pt.
..................................................................
TT_Set_Instance_Resolutions( TT_Instance instance,
TT_UShort xResolution,
TT_UShort yResolution );
Sets the target device resolutions for a given instance. The
values are expressed in dots per inch (dpi). A value of 96dpi
is typical for an SVGA display, 72dpi for a Macintosh one, and
300 to 6000dpi for printers. Default value (before a call to
this function) is 96dpi.
..................................................................
TT_Set_Instance_CharSize( TT_Instance instance,
TT_F26Dot6 charsize );
Sets the point size for a given instance. The size is expressed
in fractional (26.6) `points', where 1 point = 1/72 inch. The
default value is 10pt (before a call to this function).
For example, to use a char size of 12pt, call the function with:
TT_Set_Instance_CharSize( instance, 12 * 64 );
Fractional point sizes are thus possible.
..................................................................
TT_Set_Instance_CharSizes( TT_Instance instance,
TT_F26Dot6 charWidth,
TT_F26Dot6 charHeight );
Sets an instance's glyph width and height independently in
fractional (26.6) points. Similar to Set_Instance_CharSize()
with the exception that the horizontal and vertical glyph
dimensions can differ.
..................................................................
TT_Set_Instance_PixelSizes( TT_Instance instance,
TT_UShort pixelWidth,
TT_UShort pixelHeight,
TT_F26Dot6 pointSize );
This function can be used to specify directly the pixel sizes
and point size of a given instance, independently of device
resolutions. This is not the recommended way to do it, but can
be used for debugging or simplicity in some special cases.
Note that you _must_ provide a point size!
..................................................................
TT_Set_Instance_Transform_Flags( TT_Instance instance,
TT_Bool rotated,
TT_Bool stretched );
Sets the transform flags for a given instance. These flags are
passed to the interpreter each time a glyph is loaded within the
instance. Their role is to notify the glyph hinting mechanism
that the resulting glyph will be transformed in a special way.
Setting one of these flags to true usually disables hinting,
though this behaviour varies with each font file.
NOTE:
The glyph loader doesn't perform the rotation or the
stretching automatically; this must be done explicitly by the
client application. Use the function TT_Transform_Outline()
for that purpose.
..................................................................
TT_Get_Instance_Metrics( TT_Instance instance,
TT_Instance_Metrics* imetrics );
This call returns a given instance's current metrics. They are
returned in the `imetrics' structure, which contains, among
other things, the current point size, ppem, and device
resolution (horizontal and vertical).
..................................................................
TT_Set_Instance_Pointer( TT_Instance instance,
void* data );
For convenience purposes, each instance object has a `generic'
pointer which value is unused by the engine, but that can be set
freely by client applications through this function.
Do what you want with it, it is here to give you a chance to
link a face object to your own structures and data.
..................................................................
void* TT_Get_Instance_Pointer( TT_Instance instance )
^^^^
This function returns an instance object's generic pointer set
through TT_Set_Instance_Pointer().
..................................................................
TT_Done_Instance( TT_Instance instance );
Closes a given instance object, destroying its associated data.
Note that this is performed automatically when a face is closed
on all its child instances. However, explicit deallocation can
help in freeing the memory used by the application earlier.
..................................................................
TT_New_Glyph( TT_Face face,
TT_Glyph* glyph );
Creates a new glyph container for the glyphs of the font
described by the `face' handle. A pointer to the container is
returned in `glyph'. The face is said to be the glyph's parent.
NOTE:
A glyph is destroyed with its parent face object. However, it
is possible to delete it explicitly with TT_Done_Glyph().
..................................................................
TT_Done_Glyph( TT_Glyph glyph );
Discards a glyph container. This is also done automatically for
all glyphs when closing its parent face object.
..................................................................
TT_Load_Glyph( TT_Instance instance,
TT_Glyph glyph,
TT_UShort glyphIndex,
TT_UShort loadFlags );
Loads and processes (scales and/or hints) a glyph at a given
`instance' into the `glyph' container.
Note that `glyph' and `instance' must have the _same_ parent
face object, otherwise an error message will be returned.
`glyph_index' is the glyph's index as found in the TrueType
font. It is _not_ a character code (see the charmap functions
below).
`load_flags' is an integer that specifies which operations are
to be performed on the loaded glyph. The following values/bits
are used:
TTLOAD_SCALE_GLYPH
Indicates that the glyph must be scaled to the instance's
resolution. The pixel coordinates returned in the glyph
outline structure (see below) are then expressed in
fractional pixels represented in the 26.6 fixed point
floating format (F26Dot6).
If scaling is disabled, the coordinates returned in the
outline structure are integer font units, also called
`FUnits' by the TrueType specification.
TTLOAD_HINT_GLYPH
This flag is only valid when scaling is on. It informs the
loader that the glyph must be hinted (i.e., grid-fitted for
optimal display). Note that hinting will occur only if the
instance's transformations and metrics allow it (for
example, most font programs disable hinting automatically in
case of rotation or stretching).
When loading a hinted glyph, the metrics computed by the
loader, including the bounding box, will also be
grid-fitted.
TTLOAD_PEDANTIC
Starting with FreeType version 1.3, the bytecode interpreter
can ignore even more errors (like out-of-bound array
accesses). Using this flag it is possible to force TrueType
compliant interpretation of font programs.
TTLOAD_IGNORE_GLOBAL_ADVANCE_WIDTH
A flag to handle monospaced fonts with an incorrect global
advance width in the `hhea' table. If set, the actual
advance width value of a particular glyph will be used; if
unset, the advance widths for all glyphs are forced to be
equal to the global value.
NOTE:
You can also use the constant TTLOAD_DEFAULT, which is simply
the union of TTLOAD_SCALE_GLYPH and TTLOAD_HINT_GLYPH for most
`typical' loads.
..................................................................
TT_Get_Glyph_Outline( TT_Glyph glyph,
TT_Outline* outline );
This call returns the glyph's `outline'. This is a simple
structure which contains pointers to the data used to describe
an outline to the rasterizer. See the definition of
TT_Outline in section I.
..................................................................
TT_Get_Glyph_Metrics( TT_Glyph glyph,
TT_Glyph_Metrics* metrics );
Extracts the glyph's metrics and copies them to the `*metrics'
structure. Its format is described in section I.
If the glyph has been loaded without scaling, the values are
expressed in FUnits (integers relative to the original font grid
called the EM Square).
If the glyph has been loaded _with_ scaling, which is the
default, the values are expressed in fractional pixels in 26.6
fixed point float format (F26Dot6; 1 unit = 1/64th of a pixel).
If the glyph has been loaded with hinting, the metrics are also
grid-fitted, including the bounding box. To get the un-fitted
bbox, call TT_Get_Outline_BBox() on the glyph's outline.
NOTE:
BBox fitting occurs according to the following scheme:
#define FLOOR( x ) ( (x) & -64 )
#define CEILING( x ) ( ( (x) + 63 ) & -64 )
xMin = FLOOR( xMin );
yMin = FLOOR( yMin );
xMax = CEILING( xMax );
yMax = CEILING( yMax );
This means that the outline's width and height in pixels can be
computed simply from the fitted bbox, namely
(xMax-xMin)/64 and (yMax-yMin)/64
..................................................................
TT_Get_Glyph_Big_Metrics( TT_Glyph glyph,
TT_Big_Glyph_Metrics* metrics );
Extracts the glyph's big metrics and copies them to the
`*metrics' structure. Its format is described in section I.
If the glyph has been loaded without scaling, the values are
expressed in FUnits (integers relative to the original font grid
called the EM Square).
If the glyph has been loaded _with_ scaling, which is the
default, the values are expressed in fractional pixels in 26.6
fixed point float format (F26Dot6; 1 unit = 1/64th of a pixel).
If the glyph has been loaded with hinting, the metrics are also
grid-fitted, including the bounding box. To get the un-fitted
bbox, just call TT_Get_Outline_BBox() on the glyph's outline.
NOTE 1:
BBox fitting occurs according to the following scheme:
#define FLOOR( x ) ( (x) & -64 )
#define CEILING( x ) ( ( (x) + 63 ) & -64 )
xMin = FLOOR( xMin );
yMin = FLOOR( yMin );
xMax = CEILING( xMax );
yMax = CEILING( yMax );
This means that the outline's width and height in pixels can be
computed simply from the fitted bounding box, namely
(xMax-xMin)/64 and (yMax-yMin)/64
NOTE 2:
The vertBearingX value in `metrics' cannot be extracted for
outline glyphs -- it is defined for embedded bitmaps only.
Instead, it is set to (xMin-xMax)/2; this will center the
bounding box on the vertical `baseline'.
..................................................................
TT_Get_Glyph_Bitmap( TT_Glyph glyph,
TT_Raster_Map* bitmap,
TT_F26Dot6 xOffset,
TT_F26Dot6 yOffset );
This call converts the vectorial glyph representation contained
in the object handled by `glyph' into a bitmap.
The target bitmap is described by the `bitmap' pointer.
Clipping will be done if necessary. You can also specify an
offset to be applied before the scan-line conversion; `xOffset'
and `yOffset' must be expressed in fractional pixels (where
1 unit = 1/64th pixel).
NOTE 1:
Choosing non integer pixel offsets, i.e., values of `xOffset'
and `yOffset' that are not multiples of 64, will ruin the
hinting performed by the interpreter, and result in bad
rendering at small sizes.
NOTE 2:
The glyph's point coordinates must be scaled before calling
this function. Never call this function with a glyph that
were loaded with no scaling!
NOTE 3:
FreeType always shifts the glyph horizontally so that the left
side bearing is equal to the left side of the bounding box.
..................................................................
TT_Get_Glyph_Pixmap( TT_Glyph glyph,
TT_Raster_Map* pixmap,
TT_F26Dot6 xOffset,
TT_F26Dot6 yOffset );
This call converts the vectorial glyph representation contained
in the object handled by `glyph' into a pixmap (i.e., an
8-bit/pixel map). The result is an anti-aliased version of the
glyph (`anti-aliasing' is also known as `font-smoothing').
The target pixmap is described by the `pixmap' pointer. Note
that its width _must_ be a multiple of 4. For the definition
and description of a pixmap see Section I.
As with TT_Get_Glyph_Bitmap(), you can specify offsets to be
applied before the rendering (`xOffset' and `yOffset' must be
expressed in fractional pixel coordinates).
NOTE 1:
You don't need to supply a temporary bitmap for the
anti-aliaser. The rasterizer uses its own scheme to optimize
memory usage.
NOTE 2:
The glyph's point coordinates must be scaled before calling
this function. This means that you should never call it with
a glyph which has been loaded without scaling!
NOTE 3:
The pixmap passed to this function should always be EMPTY
(i.e., filled with zero bytes) before the call. If not,
garbage will accumulate!
NOTE 4:
FreeType always shifts the glyph horizontally so that the left
side bearing is equal to the left side of the bounding box.
..................................................................
TT_New_Outline( TT_UShort numPoints,
TT_UShort numContours,
TT_Outline* outline );
Creates a new outline object. This function creates the arrays
necessary to hold `numPoints' points and `numContours' contours,
and set `outline's pointers to them.
The new outline owns the arrays, and they will be destroyed with
it through TT_Done_Outline().
NOTE 1:
Outlines created with this function are called `user'
outlines, in contrast with the outlines returned by
TT_Get_Glyph_Outline(), which fields refer to the data
contained within a glyph object (i.e., these outlines do not
own the arrays they refer to).
NOTE 2:
User outlines aren't tracked by the engine, which means they
are not destroyed by a TT_Done_FreeType(). You have to
explicitly discard them through TT_Done_Outline() to avoid
memory leaks.
..................................................................
TT_Done_Outline( TT_Outline* outline );
Deletes an outline's data. Note that you need not destroy the
outlines returned by TT_Get_Glyph_Outline(), only those created
by TT_New_Outline().
..................................................................
TT_Copy_Outline( TT_Outline* source,
TT_Outline* target );
Copies the content of the `source' outline into the content of
the `target' outline. The two outlines must have been created
with the same dimensions (num_points and num_contours),
otherwise this function will return an error code.
..................................................................
void TT_Transform_Outline( TT_Glyph_Outline* outline,
^^^^ TT_Matrix* matrix );
Applies a simple transformation matrix on a given outline. This
will multiply each point coordinate vector by a 2x2 matrix,
which coefficients are given in the 16.16 fixed float format.
Rotation can be performed with this function.
NOTE:
This function takes an outline, and not a glyph handle, as a
parameter. This `feature' lets you apply transformations on
your own copies of glyphs.
..................................................................
void TT_Translate_Outline( TT_Glyph_Outline* outline,
^^^^ TT_Pos xOffset,
TT_Pos yOffset );
Applies a simple translation on a given outline.
NOTE:
This function takes an outline, and not a glyph handle, as a
parameter. This `feature' lets you apply translation to your
own copies of glyphs.
..................................................................
TT_Get_Outline_Bitmap( TT_Outline* outline,
TT_Raster_Map* bitmap );
Renders an outline into a bitmap. The latter must be setup by
the user before the call (i.e., it is not created by this
function, instead it must be provided by the user).
..................................................................
TT_Get_Outline_Pixmap( TT_Outline* outline,
TT_Raster_Map* pixmap );
Renders an outline into a pixmap. The latter must be setup by
the user before the call (i.e., it is not created by this
function, instead it must be provided by the user).
NOTE:
The pixmap passed to this function must always be EMPTY (i.e.,
filled with zero bytes) before the call. Otherwise, garbage may
accumulate!
..................................................................
TT_Get_Outline_BBox( TT_Outline* outline,
TT_BBox* bbox );
Returns an outline's bounding box in the `bbox' structure. Note
that the returned coordinates are not grid fitted!
NOTE:
The current release of FreeType (1.x) does compute the bounding
box for the outline's control points, and not the `exact' box
based on Bezier arcs extrema. Hence, the bbox returned by this
function may be slightly larger than necessary if the glyph
doesn't have control points at its extrema, or if it has been
rotated.
..................................................................
void TT_Transform_Vector( TT_Pos* x,
^^^^ TT_Pos* y,
TT_Matrix* matrix );
Applies a 2x2 matrix to a vector.
..................................................................
int TT_Get_CharMapCount( TT_Face face );
^^^
Gets the number of character mappings present in the TrueType
file described by the `face' handle. Returns -1 if the handle
is invalid.
IMPORTANT NOTE: ********
This function is deprecated. Get the number of character maps
from the `num_CharMaps' field in the structure returned by
TT_Get_Face_Property() instead.
..................................................................
TT_Get_CharMap_ID( TT_Face face,
TT_UShort charmapIndex,
TT_UShort* platformID,
TT_UShort* encodingID );
Returns the platform ID and platform-specific encoding ID for
the charmap numbered `charmapIndex' in the `face' object. The
total number of character mapping tables can be found in the
`num_CharMaps' field in the structure returned by
TT_Get_Face_Property().
..................................................................
TT_Get_CharMap( TT_Face face,
TT_UShort charmapIndex,
TT_CharMap* charMap );
Returns a handle for the character map number `charmapIndex' of
`face'. The handle is placed in `*charMap' and can be used
later for fast lookup with the TT_Char_Index() API function.
Charmap objects are automatically destroyed when their face
object is destroyed.
..................................................................
TT_UShort TT_Char_Index( TT_CharMap charMap,
^^^^^^^^^ TT_UShort charCode );
Applies a charMap to translate `charCode' into a glyph index
that can be used to load and address a glyph in the TrueType
file. In case of error, the undefined glyph (index 0) is
returned.
The charmap handle can be obtained with TT_Get_CharMap().
..................................................................
int TT_Get_Name_Count( TT_Face face );
^^^
Gets the number of name strings found in a face's name table.
This function will return -1 if the face handle is invalid.
IMPORTANT NOTE: ********
This function is deprecated. Get the number of name strings
from the `num_Names' field in the structure returned by
TT_Get_Face_Property() instead.
..................................................................
TT_Get_Name_ID( TT_Face face,
TT_UShort nameIndex,
TT_UShort* platformID,
TT_UShort* encodingID,
TT_UShort* languageID,
TT_UShort* nameID );
Returns the ID of a given name string, indexed by the number
`nameIndex' in a given face. The name index ranges from 0 to
`num_names' minus one; this value can be found in the structure
returned by TT_Get_Face_Property().
Each string has a `platformID', `encodingID', `languageID' and
`nameID', as defined by the TrueType specification.
The platformID is typically in the range [0,3]. Some font files
have unusual name table entries; these can be detected from
their platformID which is larger than 3.
..................................................................
TT_Get_Name_String( TT_Face face,
TT_UShort nameIndex,
TT_String** stringPtr,
TT_UShort* length );
Returns a name string's address and length. Note that an
invalid name table entry always returns NULL for `stringPtr' and
zero for `length'.
NOTE 1:
The string belongs to the face object and should not be
written to or freed by the client application.
NOTE 2:
The library does not care about endianess here! If you are
using a little-endian machine and you have to interpret the
string bytes as 16-bit-wide characters (e.g. Unicode encoded),
you must byte-swap the data because 16-bit data is stored as
big-endian in TrueType fonts, and FreeType reads in the whole
name table bytewise.
..................................................................
TT_Get_Font_Data( TT_face face,
TT_Long tag,
TT_Long offset,
void* buffer,
TT_Long* length );
Gets font or table data. Similar to the GetFontData() API of
the Windows world. You can use the macro MAKE_TT_TAG() to
generate TrueType table tags from character descriptions, like
MAKE_TT_TAG( 'e', 'b', 'l', 'c' )
Use the value 0 instead for `tag' if you want to access the
whole font file. `offset' specifies the starting offset in the
table (or the offset in the file if tag == 0), `buffer' the
address of target buffer.
Depending on the value of length, various actions are performed.
If `length' is NULL, the whole table will be loaded. An error
will be returned if `offset' is not 0. If `*length' is zero,
TT_Get_Font_Data() exits immediately, returning only the length
of the given table (in the variable `length'), or of the font
file, depending on the value of `tag'. Finally, if `*length' is
not zero, the next `length' bytes of the table (resp. the font)
are loaded into an array pointed to by `buffer', starting at
offset `offset'. Note that the `buffer' array must be large
enough to hold `length' bytes.
--------------------------------------------------------------------
--------------------------------------------------------------------
III. Error Messages
===================
Most functions return an error code, typed to TT_Error. A return
value of zero indicates no error. The error values are defined in
the file `freetype.h'. In the following table, the prefix
`TT_Err_' is omitted, e.g. `Ok' -> `TT_Err_Ok'.
Error Unprefixed Error
Code Macro Name Description
------------------------------------------------------------------
0x0000 Ok Successful function call.
Always 0!
----------------- high-level API error codes ---------------------
The following error codes are returned by the high-level API to
indicate an invalid client request.
0x0001 Invalid_Face_Handle An invalid face object handle was
passed to an API function.
0x0002 Invalid_Instance_Handle An invalid instance object handle
was passed to an API function.
0x0003 Invalid_Glyph_Handle An invalid glyph container handle
was passed to an API function.
0x0004 Invalid_CharMap_Handle An invalid charmap handle was
passed to an API function.
0x0005 Invalid_Result_Address An output parameter (a result)
was given a NULL address in an
API call.
0x0006 Invalid_Glyph_Index An invalid glyph index was passed
to an API function.
0x0007 Invalid_Argument An invalid argument was passed to
an API function. Usually, this
means a simple out-of-bounds
error.
0x0008 Could_Not_Open_File The pathname passed doesn't point
to an existing or accessible
file.
0x0009 File_Is_Not_Collection Returned by TT_Open_Collection
while trying to open a file which
isn't a collection.
0x000A Table_Missing The requested TrueType table is
missing in the font file.
0x000B Invalid_Horiz_Metrics The font's HMTX table is invalid.
Denotes a broken font.
0x000C Invalid_CharMap_Format A font's charmap entry has an
invalid format. Some other
entries may be valid though.
0x000D Invalid_PPem Invalid PPem values specified,
i.e., you are accessing a scaled
glyph without having called
TT_Set_Instance_CharSize() or
TT_Set_Instance_PixelSizes().
0x0010 Invalid_File_Format The file isn't a TrueType font or
collection.
0x0020 Invalid_Engine An invalid engine handle was
passed to one of the API
functions.
0x0021 Too_Many_Extensions The client application is trying
to initialize too many
extensions. The default max
extensions number is 8 (this
value can be changed at compile
time).
0x0022 Extensions_Unsupported This build of the engine doesn't
support extensions.
0x0023 Invalid_Extension_Id This error indicates that the
client application is trying to
use an extension that has not
been initialized yet.
0x0080 Max_Profile_Missing The max profile table is missing.
=> broken font file
0x0081 Header_Table_Missing The font header table is missing.
=> broken font file
0x0082 Horiz_Header_Missing The horizontal header is missing.
=> broken font file
0x0083 Locations_Missing The locations table is missing.
=> broken font file
0x0084 Name_Table_Missing The name table is missing.
=> broken font file
0x0085 CMap_Table_Missing The character encoding tables are
missing.
=> broken font file
0x0086 Hmtx_Table_Missing The hmtx table is missing.
=> broken font file
0x0087 OS2_Table_Missing The OS/2 table is missing.
Mac fonts doesn't have it.
0x0088 Post_Table_Missing The PostScript table is missing.
=> broken font file
0x0089 Glyf_Table_Missing The glyph table is missing.
=> broken font file
----------------- memory component error codes -------------------
0x0100 Out_Of_Memory An operation couldn't be
performed due to memory
exhaustion.
----------------- file component error codes ---------------------
0x0200 Invalid_File_Offset Trying to seek to an invalid
portion of the font file.
Denotes a broken file.
0x0201 Invalid_File_Read Trying to read an invalid portion
of the font file. Denotes a
broken file.
0x0202 Invalid_Frame_Access Trying to frame an invalid
portion of the font file.
Denotes a broken file.
----------------- glyph loader error codes -----------------------
These errors are produced by the glyph loader. They denote an
invalid glyph record within the font file.
0x0300 Too_Many_Points The glyph has too many points to
be valid for its font file.
0x0301 Too_Many_Contours The glyph has too many contours
to be valid for its font file.
0x0302 Invalid_Composite_Glyph A composite glyph's description
is broken.
0x0303 Too_Many_Ins The glyph has too many
instructions to be valid for its
font file.
----------------- byte-code interpreter error codes --------------
These error codes are produced by the TrueType byte-code
interpreter. They usually indicate a broken font file or a broken
glyph within a font.
0x0400 Invalid_Opcode Found an invalid opcode in a
TrueType byte-code stream.
0x0401 Too_Few_Arguments An opcode was invoked with too
few arguments on the stack.
0x0402 Stack_Overflow The interpreter's stack has been
filled up and operations can't
continue.
0x0403 Code_Overflow The byte-code stream runs out of
its valid bounds.
0x0404 Bad_Argument A function received an invalid
argument.
0x0405 Divide_By_Zero A division by 0 operation was
queried by the interpreter
program.
0x0406 Storage_Overflow The program tried to access data
outside of its storage area.
0x0407 Cvt_Overflow The program tried to access data
outside of its control value
table.
0x0408 Invalid_Reference The program tried to reference an
invalid point, zone, or contour.
0x0409 Invalid_Distance The program tried to use an
invalid distance.
0x040A Interpolate_Twilight The program tried to interpolate
twilight points.
0x040B Debug_Opcode The now invalid `debug' opcode
was found in the byte-code
stream.
0x040C ENDF_In_Exec_Stream A misplaced ENDF was encountered
in the byte-code stream.
0x040D Out_Of_CodeRanges The program tried to allocate too
much code ranges (this is really
an engine internal error that
should never happen).
0x040E Nested_DEFS Nested function definitions
encountered.
0x040F Invalid_CodeRange The program tried to access an
invalid code range.
0x0410 Invalid_Displacement The program tried to use an
invalid displacement.
0x0411 Execution_Too_Long In order to get rid of `poison'
fonts, the interpreter produces
this error if more than one
million opcodes have been
interpreted in a single glyph
program. This detects infinite
loops softly.
----------------- internal failure error codes -------------------
These error codes are produced if an incoherent library state has
been detected. All of these reflect a severe bug in the engine
(or a severe memory corruption due to massive overwrites by your
application into the library's data)!
If you do encounter a font that makes one of the test programs
produce such an error, please report it!
0x0500 Nested_Frame_Access
0x0501 Invalid_Cache_List
0x0502 Could_Not_Find_Context
0x0503 Unlisted_Object
----------------- scan-line converter error codes ----------------
These error codes are produced by the raster component. They
indicate that an outline structure was incoherently set up, or
that you are trying to render a horribly complex glyph.
They should be _extremely_ rare, however.
0x0600 Raster_Pool_Overflow Render pool overflow. This should
never happen in this release.
0x0601 Raster_Negative_Height A negative height was produced.
0x0602 Raster_Invalid_Value The outline data wasn't set
properly. Check that:
points >= endContours[contours]
0x0603 Raster_Not_Initialized You did not call
TT_Init_FreeType()!
--- end of apiref.txt ---
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