FreeType-2.8 API Reference

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REQUEST EXIT

Cache Sub-System

Synopsis

This section describes the FreeType 2 cache sub-system, which is used to limit the number of concurrently opened FT_Face and FT_Size objects, as well as caching information like character maps and glyph images while limiting their maximum memory usage.

The cache is highly portable and thus doesn't know anything about the fonts installed on your system, or how to access them. This implies the following scheme:

First, available or installed font faces are uniquely identified by FTC_FaceID values, provided to the cache by the client. Note that the cache only stores and compares these values, and doesn't try to interpret them in any way.

Second, the cache calls, only when needed, a client-provided function to convert an FTC_FaceID into a new FT_Face object. The latter is then completely managed by the cache, including its termination through FT_Done_Face. To monitor termination of face objects, the finalizer callback in the ‘generic’ field of the FT_Face object can be used, which might also be used to store the FTC_FaceID of the face.

Clients are free to map face IDs to anything else. The most simple usage is to associate them to a (pathname,face_index) pair that is used to call FT_New_Face. However, more complex schemes are also possible.

Note that for the cache to work correctly, the face ID values must be persistent, which means that the contents they point to should not change at runtime, or that their value should not become invalid.

If this is unavoidable (e.g., when a font is uninstalled at runtime), you should call FTC_Manager_RemoveFaceID as soon as possible, to let the cache get rid of any references to the old FTC_FaceID it may keep internally. Failure to do so will lead to incorrect behaviour or even crashes.

If you need lots of small bitmaps, it is much more memory efficient to call FTC_SBitCache_New followed by FTC_SBitCache_Lookup. This returns FTC_SBitRec structures, which are used to store small bitmaps directly. (A small bitmap is one whose metrics and dimensions all fit into 8-bit integers).

typedef FT_Error (*FTC_Face_Requester)( FTC_FaceID face_id, FT_Library library, FT_Pointer req_data, FT_Face* aface );

FT_EXPORT( FT_Error ) FTC_Manager_New( FT_Library library, FT_UInt max_faces, FT_UInt max_sizes, FT_ULong max_bytes, FTC_Face_Requester requester, FT_Pointer req_data, FTC_Manager *amanager );

FT_EXPORT( FT_Error ) FTC_ImageCache_Lookup( FTC_ImageCache cache, FTC_ImageType type, FT_UInt gindex, FT_Glyph *aglyph, FTC_Node *anode );

FT_EXPORT( FT_Error ) FTC_SBitCache_Lookup( FTC_SBitCache cache, FTC_ImageType type, FT_UInt gindex, FTC_SBit *sbit, FTC_Node *anode );

FT_EXPORT( FT_UInt ) FTC_CMapCache_Lookup( FTC_CMapCache cache, FTC_FaceID face_id, FT_Int cmap_index, FT_UInt32 char_code );

FT_EXPORT( FT_Error ) FTC_ImageCache_LookupScaler( FTC_ImageCache cache, FTC_Scaler scaler, FT_ULong load_flags, FT_UInt gindex, FT_Glyph *aglyph, FTC_Node *anode );

typedef struct FTC_SBitRec_ { FT_Byte width; FT_Byte height; FT_Char left; FT_Char top; FT_Byte format; FT_Byte max_grays; FT_Short pitch; FT_Char xadvance; FT_Char yadvance; FT_Byte* buffer; } FTC_SBitRec;

FT_EXPORT( FT_Error ) FTC_SBitCache_LookupScaler( FTC_SBitCache cache, FTC_Scaler scaler, FT_ULong load_flags, FT_UInt gindex, FTC_SBit *sbit, FTC_Node *anode );

face_id	The source face ID.
width	The character width.
height	The character height.
pixel	A Boolean. If 1, the ‘width’ and ‘height’ fields are interpreted as integer pixel character sizes. Otherwise, they are expressed as 1/64th of points.
x_res	Only used when ‘pixel’ is value 0 to indicate the horizontal resolution in dpi.
y_res	Only used when ‘pixel’ is value 0 to indicate the vertical resolution in dpi.

FTC_Manager
FTC_FaceID	FTC_SBit
FTC_Face_Requester	FTC_SBitCache
	FTC_SBitCache_New
FTC_Manager_New	FTC_SBitCache_Lookup
FTC_Manager_Reset
FTC_Manager_Done	FTC_CMapCache
FTC_Manager_LookupFace	FTC_CMapCache_New
FTC_Manager_LookupSize	FTC_CMapCache_Lookup
FTC_Manager_RemoveFaceID
	FTC_ScalerRec
FTC_Node	FTC_Scaler
FTC_Node_Unref	FTC_ImageTypeRec
	FTC_ImageType
FTC_ImageCache	FTC_ImageCache_LookupScaler
FTC_ImageCache_New	FTC_SBitRec
FTC_ImageCache_Lookup	FTC_SBitCache_LookupScaler

face_id	The face ID to resolve.
library	A handle to a FreeType library object.
req_data	Application-provided request data (see note below).

library	The parent FreeType library handle to use.
max_faces	Maximum number of opened FT_Face objects managed by this cache instance. Use 0 for defaults.
max_sizes	Maximum number of opened FT_Size objects managed by this cache instance. Use 0 for defaults.
max_bytes	Maximum number of bytes to use for cached data nodes. Use 0 for defaults. Note that this value does not account for managed FT_Face and FT_Size objects.
requester	An application-provided callback used to translate face IDs into real FT_Face objects.
req_data	A generic pointer that is passed to the requester each time it is called (see FTC_Face_Requester).

manager	A handle to the cache manager.
face_id	The ID of the face object.

manager	The cache manager handle.
face_id	The FTC_FaceID to be removed.

cache	A handle to the source glyph image cache.
type	A pointer to a glyph image type descriptor.
gindex	The glyph index to retrieve.

aglyph	The corresponding FT_Glyph object. 0 in case of failure.
anode	Used to return the address of the corresponding cache node after incrementing its reference count (see note below).

cache	A handle to the source sbit cache.
type	A pointer to the glyph image type descriptor.
gindex	The glyph index.

sbit	A handle to a small bitmap descriptor.
anode	Used to return the address of the corresponding cache node after incrementing its reference count (see note below).

cache	A charmap cache handle.
face_id	The source face ID.
cmap_index	The index of the charmap in the source face. Any negative value means to use the cache FT_Face's default charmap.
char_code	The character code (in the corresponding charmap).

face_id	The face ID.
width	The width in pixels.
height	The height in pixels.
flags	The load flags, as in FT_Load_Glyph.

cache	A handle to the source glyph image cache.
scaler	A pointer to a scaler descriptor.
load_flags	The corresponding load flags.
gindex	The glyph index to retrieve.

width	The bitmap width in pixels.
height	The bitmap height in pixels.
left	The horizontal distance from the pen position to the left bitmap border (a.k.a. ‘left side bearing’, or ‘lsb’).
top	The vertical distance from the pen position (on the baseline) to the upper bitmap border (a.k.a. ‘top side bearing’). The distance is positive for upwards y coordinates.
format	The format of the glyph bitmap (monochrome or gray).
max_grays	Maximum gray level value (in the range 1 to 255).
pitch	The number of bytes per bitmap line. May be positive or negative.
xadvance	The horizontal advance width in pixels.
yadvance	The vertical advance height in pixels.
buffer	A pointer to the bitmap pixels.

FreeType-2.8 API Reference

Cache Sub-System

Synopsis

FTC_Manager

FTC_FaceID

note

FTC_Face_Requester

input

output

return

note

FTC_Manager_New

input

output

return

FTC_Manager_Reset

inout

FTC_Manager_Done

input

FTC_Manager_LookupFace

input

output

return

note

FTC_Manager_LookupSize

input

output

return

note

note

FTC_Manager_RemoveFaceID

input

note

FTC_Node

FTC_Node_Unref

input

FTC_ImageCache

FTC_ImageCache_New

input

output

return

FTC_ImageCache_Lookup

input

output

return

note

FTC_SBit

FTC_SBitCache

FTC_SBitCache_New

input

output

return

FTC_SBitCache_Lookup

input

output

return

note

FTC_CMapCache

FTC_CMapCache_New

input

output

return

note

FTC_CMapCache_Lookup

input

return

FTC_ScalerRec

fields

note

FTC_Scaler

FTC_ImageTypeRec

fields

FTC_ImageType

FTC_ImageCache_LookupScaler

input

output

return

note

FTC_SBitRec

fields