tor-browser

ftcache.h (34179B)

---

/****************************************************************************
*
* ftcache.h
*
*   FreeType Cache subsystem (specification).
*
* Copyright (C) 1996-2025 by
* David Turner, Robert Wilhelm, and Werner Lemberg.
*
* This file is part of the FreeType project, and may only be used,
* modified, and distributed under the terms of the FreeType project
* license, LICENSE.TXT.  By continuing to use, modify, or distribute
* this file you indicate that you have read the license and
* understand and accept it fully.
*
*/


#ifndef FTCACHE_H_
#define FTCACHE_H_


#include <freetype/ftglyph.h>


FT_BEGIN_HEADER


 /**************************************************************************
  *
  * @section:
  *   cache_subsystem
  *
  * @title:
  *   Cache Sub-System
  *
  * @abstract:
  *   How to cache face, size, and glyph data with FreeType~2.
  *
  * @description:
  *   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.
  *
  *   Note that all types and functions begin with the `FTC_` prefix rather
  *   than the usual `FT_` prefix in the rest of FreeType.
  *
  *   The cache is highly portable and, thus, doesn't know anything about
  *   the fonts installed on your system, or how to access them.  Therefore,
  *   it requires the following.
  *
  *   * @FTC_FaceID, an arbitrary non-zero value that uniquely identifies
  *     available or installed font faces, has to be 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, but they
  *     have to be persistent on the client side.
  *
  *   * @FTC_Face_Requester, a method to convert an @FTC_FaceID into a new
  *     @FT_Face object when necessary, has to be provided to the cache by
  *     the client.  The @FT_Face object is 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 useful.  The most simple
  *   usage is, for example, to associate them to a `{pathname,face_index}`
  *   pair that is then used by @FTC_Face_Requester 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 in @FTC_Face_Requester.
  *
  *   To use the cache, start with calling @FTC_Manager_New to create a new
  *   @FTC_Manager object, which models a single cache instance.  You can
  *   then look up @FT_Face and @FT_Size objects with
  *   @FTC_Manager_LookupFace and @FTC_Manager_LookupSize, respectively, and
  *   use them in any FreeType work stream.  You can also cache other
  *   FreeType objects as follows.
  *
  *   * If you want to use the charmap caching, call @FTC_CMapCache_New,
  *     then later use @FTC_CMapCache_Lookup to perform the equivalent of
  *     @FT_Get_Char_Index, only much faster.
  *
  *   * If you want to use the @FT_Glyph caching, call @FTC_ImageCache_New,
  *     then later use @FTC_ImageCache_Lookup to retrieve the corresponding
  *     @FT_Glyph objects from the cache.
  *
  *   * 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).
  *
  * @order:
  *   FTC_Manager
  *   FTC_FaceID
  *   FTC_Face_Requester
  *
  *   FTC_Manager_New
  *   FTC_Manager_Reset
  *   FTC_Manager_Done
  *   FTC_Manager_LookupFace
  *   FTC_Manager_LookupSize
  *   FTC_Manager_RemoveFaceID
  *
  *   FTC_Node
  *   FTC_Node_Unref
  *
  *   FTC_ImageCache
  *   FTC_ImageCache_New
  *   FTC_ImageCache_Lookup
  *
  *   FTC_SBit
  *   FTC_SBitCache
  *   FTC_SBitCache_New
  *   FTC_SBitCache_Lookup
  *
  *   FTC_CMapCache
  *   FTC_CMapCache_New
  *   FTC_CMapCache_Lookup
  *
  *************************************************************************/


 /*************************************************************************/
 /*************************************************************************/
 /*************************************************************************/
 /*****                                                               *****/
 /*****                    BASIC TYPE DEFINITIONS                     *****/
 /*****                                                               *****/
 /*************************************************************************/
 /*************************************************************************/
 /*************************************************************************/


 /**************************************************************************
  *
  * @type:
  *   FTC_FaceID
  *
  * @description:
  *   An opaque pointer type that is used to identity face objects.  The
  *   contents of such objects is application-dependent.
  *
  *   These pointers are typically used to point to a user-defined structure
  *   containing a font file path, and face index.
  *
  * @note:
  *   Never use `NULL` as a valid @FTC_FaceID.
  *
  *   Face IDs are passed by the client to the cache manager that calls,
  *   when needed, the @FTC_Face_Requester to translate them into new
  *   @FT_Face objects.
  *
  *   If the content of a given face ID changes at runtime, or if the value
  *   becomes invalid (e.g., when uninstalling a font), you should
  *   immediately call @FTC_Manager_RemoveFaceID before any other cache
  *   function.
  *
  *   Failure to do so will result in incorrect behaviour or even memory
  *   leaks and crashes.
  */
 typedef FT_Pointer  FTC_FaceID;


 /**************************************************************************
  *
  * @functype:
  *   FTC_Face_Requester
  *
  * @description:
  *   A callback function provided by client applications.  It is used by
  *   the cache manager to translate a given @FTC_FaceID into a new valid
  *   @FT_Face object, on demand.
  *
  * @input:
  *   face_id ::
  *     The face ID to resolve.
  *
  *   library ::
  *     A handle to a FreeType library object.
  *
  *   req_data ::
  *     Application-provided request data (see note below).
  *
  * @output:
  *   aface ::
  *     A new @FT_Face handle.
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The third parameter `req_data` is the same as the one passed by the
  *   client when @FTC_Manager_New is called.
  *
  *   The face requester should not perform funny things on the returned
  *   face object, like creating a new @FT_Size for it, or setting a
  *   transformation through @FT_Set_Transform!
  */
 typedef FT_Error
 (*FTC_Face_Requester)( FTC_FaceID  face_id,
                        FT_Library  library,
                        FT_Pointer  req_data,
                        FT_Face*    aface );

 /* */


 /*************************************************************************/
 /*************************************************************************/
 /*************************************************************************/
 /*****                                                               *****/
 /*****                      CACHE MANAGER OBJECT                     *****/
 /*****                                                               *****/
 /*************************************************************************/
 /*************************************************************************/
 /*************************************************************************/


 /**************************************************************************
  *
  * @type:
  *   FTC_Manager
  *
  * @description:
  *   This object corresponds to one instance of the cache-subsystem.  It is
  *   used to cache one or more @FT_Face objects, along with corresponding
  *   @FT_Size objects.
  *
  *   The manager intentionally limits the total number of opened @FT_Face
  *   and @FT_Size objects to control memory usage.  See the `max_faces` and
  *   `max_sizes` parameters of @FTC_Manager_New.
  *
  *   The manager is also used to cache 'nodes' of various types while
  *   limiting their total memory usage.
  *
  *   All limitations are enforced by keeping lists of managed objects in
  *   most-recently-used order, and flushing old nodes to make room for new
  *   ones.
  */
 typedef struct FTC_ManagerRec_*  FTC_Manager;


 /**************************************************************************
  *
  * @type:
  *   FTC_Node
  *
  * @description:
  *   An opaque handle to a cache node object.  Each cache node is
  *   reference-counted.  A node with a count of~0 might be flushed out of a
  *   full cache whenever a lookup request is performed.
  *
  *   If you look up nodes, you have the ability to 'acquire' them, i.e., to
  *   increment their reference count.  This will prevent the node from
  *   being flushed out of the cache until you explicitly 'release' it (see
  *   @FTC_Node_Unref).
  *
  *   See also @FTC_SBitCache_Lookup and @FTC_ImageCache_Lookup.
  */
 typedef struct FTC_NodeRec_*  FTC_Node;


 /**************************************************************************
  *
  * @function:
  *   FTC_Manager_New
  *
  * @description:
  *   Create a new cache manager.
  *
  * @input:
  *   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).
  *
  * @output:
  *   amanager ::
  *     A handle to a new manager object.  0~in case of failure.
  *
  * @return:
  *   FreeType error code.  0~means success.
  */
 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 );


 /**************************************************************************
  *
  * @function:
  *   FTC_Manager_Reset
  *
  * @description:
  *   Empty a given cache manager.  This simply gets rid of all the
  *   currently cached @FT_Face and @FT_Size objects within the manager.
  *
  * @inout:
  *   manager ::
  *     A handle to the manager.
  */
 FT_EXPORT( void )
 FTC_Manager_Reset( FTC_Manager  manager );


 /**************************************************************************
  *
  * @function:
  *   FTC_Manager_Done
  *
  * @description:
  *   Destroy a given manager after emptying it.
  *
  * @input:
  *   manager ::
  *     A handle to the target cache manager object.
  */
 FT_EXPORT( void )
 FTC_Manager_Done( FTC_Manager  manager );


 /**************************************************************************
  *
  * @function:
  *   FTC_Manager_LookupFace
  *
  * @description:
  *   Retrieve the @FT_Face object that corresponds to a given face ID
  *   through a cache manager.
  *
  * @input:
  *   manager ::
  *     A handle to the cache manager.
  *
  *   face_id ::
  *     The ID of the face object.
  *
  * @output:
  *   aface ::
  *     A handle to the face object.
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The returned @FT_Face object is always owned by the manager.  You
  *   should never try to discard it yourself.
  *
  *   The @FT_Face object doesn't necessarily have a current size object
  *   (i.e., face->size can be~0).  If you need a specific 'font size', use
  *   @FTC_Manager_LookupSize instead.
  *
  *   Never change the face's transformation matrix (i.e., never call the
  *   @FT_Set_Transform function) on a returned face!  If you need to
  *   transform glyphs, do it yourself after glyph loading.
  *
  *   When you perform a lookup, out-of-memory errors are detected _within_
  *   the lookup and force incremental flushes of the cache until enough
  *   memory is released for the lookup to succeed.
  *
  *   If a lookup fails with `FT_Err_Out_Of_Memory` the cache has already
  *   been completely flushed, and still no memory was available for the
  *   operation.
  */
 FT_EXPORT( FT_Error )
 FTC_Manager_LookupFace( FTC_Manager  manager,
                         FTC_FaceID   face_id,
                         FT_Face     *aface );


 /**************************************************************************
  *
  * @struct:
  *   FTC_ScalerRec
  *
  * @description:
  *   A structure used to describe a given character size in either pixels
  *   or points to the cache manager.  See @FTC_Manager_LookupSize.
  *
  * @fields:
  *   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
  *     1/64 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.
  *
  * @note:
  *   This type is mainly used to retrieve @FT_Size objects through the
  *   cache manager.
  */
 typedef struct  FTC_ScalerRec_
 {
   FTC_FaceID  face_id;
   FT_UInt     width;
   FT_UInt     height;
   FT_Int      pixel;
   FT_UInt     x_res;
   FT_UInt     y_res;

 } FTC_ScalerRec;


 /**************************************************************************
  *
  * @struct:
  *   FTC_Scaler
  *
  * @description:
  *   A handle to an @FTC_ScalerRec structure.
  */
 typedef struct FTC_ScalerRec_*  FTC_Scaler;


 /**************************************************************************
  *
  * @function:
  *   FTC_Manager_LookupSize
  *
  * @description:
  *   Retrieve the @FT_Size object that corresponds to a given
  *   @FTC_ScalerRec pointer through a cache manager.
  *
  * @input:
  *   manager ::
  *     A handle to the cache manager.
  *
  *   scaler ::
  *     A scaler handle.
  *
  * @output:
  *   asize ::
  *     A handle to the size object.
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The returned @FT_Size object is always owned by the manager.  You
  *   should never try to discard it by yourself.
  *
  *   You can access the parent @FT_Face object simply as `size->face` if
  *   you need it.  Note that this object is also owned by the manager.
  *
  * @note:
  *   When you perform a lookup, out-of-memory errors are detected _within_
  *   the lookup and force incremental flushes of the cache until enough
  *   memory is released for the lookup to succeed.
  *
  *   If a lookup fails with `FT_Err_Out_Of_Memory` the cache has already
  *   been completely flushed, and still no memory is available for the
  *   operation.
  */
 FT_EXPORT( FT_Error )
 FTC_Manager_LookupSize( FTC_Manager  manager,
                         FTC_Scaler   scaler,
                         FT_Size     *asize );


 /**************************************************************************
  *
  * @function:
  *   FTC_Node_Unref
  *
  * @description:
  *   Decrement a cache node's internal reference count.  When the count
  *   reaches 0, it is not destroyed but becomes eligible for subsequent
  *   cache flushes.
  *
  * @input:
  *   node ::
  *     The cache node handle.
  *
  *   manager ::
  *     The cache manager handle.
  */
 FT_EXPORT( void )
 FTC_Node_Unref( FTC_Node     node,
                 FTC_Manager  manager );


 /**************************************************************************
  *
  * @function:
  *   FTC_Manager_RemoveFaceID
  *
  * @description:
  *   A special function used to indicate to the cache manager that a given
  *   @FTC_FaceID is no longer valid, either because its content changed, or
  *   because it was deallocated or uninstalled.
  *
  * @input:
  *   manager ::
  *     The cache manager handle.
  *
  *   face_id ::
  *     The @FTC_FaceID to be removed.
  *
  * @note:
  *   This function flushes all nodes from the cache corresponding to this
  *   `face_id`, with the exception of nodes with a non-null reference
  *   count.
  *
  *   Such nodes are however modified internally so as to never appear in
  *   later lookups with the same `face_id` value, and to be immediately
  *   destroyed when released by all their users.
  *
  */
 FT_EXPORT( void )
 FTC_Manager_RemoveFaceID( FTC_Manager  manager,
                           FTC_FaceID   face_id );


 /**************************************************************************
  *
  * @type:
  *   FTC_CMapCache
  *
  * @description:
  *   An opaque handle used to model a charmap cache.  This cache is to hold
  *   character codes -> glyph indices mappings.
  *
  */
 typedef struct FTC_CMapCacheRec_*  FTC_CMapCache;


 /**************************************************************************
  *
  * @function:
  *   FTC_CMapCache_New
  *
  * @description:
  *   Create a new charmap cache.
  *
  * @input:
  *   manager ::
  *     A handle to the cache manager.
  *
  * @output:
  *   acache ::
  *     A new cache handle.  `NULL` in case of error.
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   Like all other caches, this one will be destroyed with the cache
  *   manager.
  *
  */
 FT_EXPORT( FT_Error )
 FTC_CMapCache_New( FTC_Manager     manager,
                    FTC_CMapCache  *acache );


 /**************************************************************************
  *
  * @function:
  *   FTC_CMapCache_Lookup
  *
  * @description:
  *   Translate a character code into a glyph index, using the charmap
  *   cache.
  *
  * @input:
  *   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).
  *
  * @return:
  *    Glyph index.  0~means 'no glyph'.
  *
  */
 FT_EXPORT( FT_UInt )
 FTC_CMapCache_Lookup( FTC_CMapCache  cache,
                       FTC_FaceID     face_id,
                       FT_Int         cmap_index,
                       FT_UInt32      char_code );


 /*************************************************************************/
 /*************************************************************************/
 /*************************************************************************/
 /*****                                                               *****/
 /*****                       IMAGE CACHE OBJECT                      *****/
 /*****                                                               *****/
 /*************************************************************************/
 /*************************************************************************/
 /*************************************************************************/


 /**************************************************************************
  *
  * @struct:
  *   FTC_ImageTypeRec
  *
  * @description:
  *   A structure used to model the type of images in a glyph cache.
  *
  * @fields:
  *   face_id ::
  *     The face ID.
  *
  *   width ::
  *     The width in pixels.
  *
  *   height ::
  *     The height in pixels.
  *
  *   flags ::
  *     The load flags, as in @FT_Load_Glyph.
  *
  */
 typedef struct  FTC_ImageTypeRec_
 {
   FTC_FaceID  face_id;
   FT_UInt     width;
   FT_UInt     height;
   FT_Int32    flags;

 } FTC_ImageTypeRec;


 /**************************************************************************
  *
  * @type:
  *   FTC_ImageType
  *
  * @description:
  *   A handle to an @FTC_ImageTypeRec structure.
  *
  */
 typedef struct FTC_ImageTypeRec_*  FTC_ImageType;


 /* */


#define FTC_IMAGE_TYPE_COMPARE( d1, d2 )      \
         ( (d1)->face_id == (d2)->face_id && \
           (d1)->width   == (d2)->width   && \
           (d1)->flags   == (d2)->flags   )


 /**************************************************************************
  *
  * @type:
  *   FTC_ImageCache
  *
  * @description:
  *   A handle to a glyph image cache object.  They are designed to hold
  *   many distinct glyph images while not exceeding a certain memory
  *   threshold.
  */
 typedef struct FTC_ImageCacheRec_*  FTC_ImageCache;


 /**************************************************************************
  *
  * @function:
  *   FTC_ImageCache_New
  *
  * @description:
  *   Create a new glyph image cache.
  *
  * @input:
  *   manager ::
  *     The parent manager for the image cache.
  *
  * @output:
  *   acache ::
  *     A handle to the new glyph image cache object.
  *
  * @return:
  *   FreeType error code.  0~means success.
  */
 FT_EXPORT( FT_Error )
 FTC_ImageCache_New( FTC_Manager      manager,
                     FTC_ImageCache  *acache );


 /**************************************************************************
  *
  * @function:
  *   FTC_ImageCache_Lookup
  *
  * @description:
  *   Retrieve a given glyph image from a glyph image cache.
  *
  * @input:
  *   cache ::
  *     A handle to the source glyph image cache.
  *
  *   type ::
  *     A pointer to a glyph image type descriptor.
  *
  *   gindex ::
  *     The glyph index to retrieve.
  *
  * @output:
  *   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).
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The returned glyph is owned and managed by the glyph image cache.
  *   Never try to transform or discard it manually!  You can however create
  *   a copy with @FT_Glyph_Copy and modify the new one.
  *
  *   If `anode` is _not_ `NULL`, it receives the address of the cache node
  *   containing the glyph image, after increasing its reference count.
  *   This ensures that the node (as well as the @FT_Glyph) will always be
  *   kept in the cache until you call @FTC_Node_Unref to 'release' it.
  *
  *   If `anode` is `NULL`, the cache node is left unchanged, which means
  *   that the @FT_Glyph could be flushed out of the cache on the next call
  *   to one of the caching sub-system APIs.  Don't assume that it is
  *   persistent!
  */
 FT_EXPORT( FT_Error )
 FTC_ImageCache_Lookup( FTC_ImageCache  cache,
                        FTC_ImageType   type,
                        FT_UInt         gindex,
                        FT_Glyph       *aglyph,
                        FTC_Node       *anode );


 /**************************************************************************
  *
  * @function:
  *   FTC_ImageCache_LookupScaler
  *
  * @description:
  *   A variant of @FTC_ImageCache_Lookup that uses an @FTC_ScalerRec to
  *   specify the face ID and its size.
  *
  * @input:
  *   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.
  *
  * @output:
  *   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).
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The returned glyph is owned and managed by the glyph image cache.
  *   Never try to transform or discard it manually!  You can however create
  *   a copy with @FT_Glyph_Copy and modify the new one.
  *
  *   If `anode` is _not_ `NULL`, it receives the address of the cache node
  *   containing the glyph image, after increasing its reference count.
  *   This ensures that the node (as well as the @FT_Glyph) will always be
  *   kept in the cache until you call @FTC_Node_Unref to 'release' it.
  *
  *   If `anode` is `NULL`, the cache node is left unchanged, which means
  *   that the @FT_Glyph could be flushed out of the cache on the next call
  *   to one of the caching sub-system APIs.  Don't assume that it is
  *   persistent!
  *
  *   Calls to @FT_Set_Char_Size and friends have no effect on cached
  *   glyphs; you should always use the FreeType cache API instead.
  */
 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 );


 /**************************************************************************
  *
  * @type:
  *   FTC_SBit
  *
  * @description:
  *   A handle to a small bitmap descriptor.  See the @FTC_SBitRec structure
  *   for details.
  */
 typedef struct FTC_SBitRec_*  FTC_SBit;


 /**************************************************************************
  *
  * @struct:
  *   FTC_SBitRec
  *
  * @description:
  *   A very compact structure used to describe a small glyph bitmap.
  *
  * @fields:
  *   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.
  */
 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;


 /**************************************************************************
  *
  * @type:
  *   FTC_SBitCache
  *
  * @description:
  *   A handle to a small bitmap cache.  These are special cache objects
  *   used to store small glyph bitmaps (and anti-aliased pixmaps) in a much
  *   more efficient way than the traditional glyph image cache implemented
  *   by @FTC_ImageCache.
  */
 typedef struct FTC_SBitCacheRec_*  FTC_SBitCache;


 /**************************************************************************
  *
  * @function:
  *   FTC_SBitCache_New
  *
  * @description:
  *   Create a new cache to store small glyph bitmaps.
  *
  * @input:
  *   manager ::
  *     A handle to the source cache manager.
  *
  * @output:
  *   acache ::
  *     A handle to the new sbit cache.  `NULL` in case of error.
  *
  * @return:
  *   FreeType error code.  0~means success.
  */
 FT_EXPORT( FT_Error )
 FTC_SBitCache_New( FTC_Manager     manager,
                    FTC_SBitCache  *acache );


 /**************************************************************************
  *
  * @function:
  *   FTC_SBitCache_Lookup
  *
  * @description:
  *   Look up a given small glyph bitmap in a given sbit cache and 'lock' it
  *   to prevent its flushing from the cache until needed.
  *
  * @input:
  *   cache ::
  *     A handle to the source sbit cache.
  *
  *   type ::
  *     A pointer to the glyph image type descriptor.
  *
  *   gindex ::
  *     The glyph index.
  *
  * @output:
  *   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).
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The small bitmap descriptor and its bit buffer are owned by the cache
  *   and should never be freed by the application.  They might as well
  *   disappear from memory on the next cache lookup, so don't treat them as
  *   persistent data.
  *
  *   The descriptor's `buffer` field is set to~0 to indicate a missing
  *   glyph bitmap.
  *
  *   If `anode` is _not_ `NULL`, it receives the address of the cache node
  *   containing the bitmap, after increasing its reference count.  This
  *   ensures that the node (as well as the image) will always be kept in
  *   the cache until you call @FTC_Node_Unref to 'release' it.
  *
  *   If `anode` is `NULL`, the cache node is left unchanged, which means
  *   that the bitmap could be flushed out of the cache on the next call to
  *   one of the caching sub-system APIs.  Don't assume that it is
  *   persistent!
  */
 FT_EXPORT( FT_Error )
 FTC_SBitCache_Lookup( FTC_SBitCache    cache,
                       FTC_ImageType    type,
                       FT_UInt          gindex,
                       FTC_SBit        *sbit,
                       FTC_Node        *anode );


 /**************************************************************************
  *
  * @function:
  *   FTC_SBitCache_LookupScaler
  *
  * @description:
  *   A variant of @FTC_SBitCache_Lookup that uses an @FTC_ScalerRec to
  *   specify the face ID and its size.
  *
  * @input:
  *   cache ::
  *     A handle to the source sbit cache.
  *
  *   scaler ::
  *     A pointer to the scaler descriptor.
  *
  *   load_flags ::
  *     The corresponding load flags.
  *
  *   gindex ::
  *     The glyph index.
  *
  * @output:
  *   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).
  *
  * @return:
  *   FreeType error code.  0~means success.
  *
  * @note:
  *   The small bitmap descriptor and its bit buffer are owned by the cache
  *   and should never be freed by the application.  They might as well
  *   disappear from memory on the next cache lookup, so don't treat them as
  *   persistent data.
  *
  *   The descriptor's `buffer` field is set to~0 to indicate a missing
  *   glyph bitmap.
  *
  *   If `anode` is _not_ `NULL`, it receives the address of the cache node
  *   containing the bitmap, after increasing its reference count.  This
  *   ensures that the node (as well as the image) will always be kept in
  *   the cache until you call @FTC_Node_Unref to 'release' it.
  *
  *   If `anode` is `NULL`, the cache node is left unchanged, which means
  *   that the bitmap could be flushed out of the cache on the next call to
  *   one of the caching sub-system APIs.  Don't assume that it is
  *   persistent!
  */
 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 );

 /* */


FT_END_HEADER

#endif /* FTCACHE_H_ */


/* END */