ref: fc15ebe0a629acf769ed8976e3d5b84ee4e01236
dir: /include/freetype/otsvg.h/
/****************************************************************************
*
* otsvg.h
*
* Interface for OT-SVG support related things (specification).
*
* Copyright (C) 2022 by
* David Turner, Robert Wilhelm, Werner Lemberg, and Moazin Khatti.
*
* 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 OTSVG_H_
#define OTSVG_H_
#include <freetype/freetype.h>
#ifdef FREETYPE_H
#error "freetype.h of FreeType 1 has been loaded!"
#error "Please fix the directory search order for header files"
#error "so that freetype.h of FreeType 2 is found first."
#endif
FT_BEGIN_HEADER
/**************************************************************************
*
* @section:
* svg_fonts
*
* @title:
* OpenType SVG Fonts
*
* @abstract:
* OT-SVG API between FreeType and an external SVG rendering library.
*
* @description:
* This section describes the four hooks necessary to render SVG
* 'documents' that are contained in an OpenType font's 'SVG~' table.
*
* For more information on the implementation, see our standard hooks
* based on 'librsvg' in the [FreeType Demo
* Programs](https://gitlab.freedesktop.org/freetype/freetype-demos)
* repository.
*
*/
/**************************************************************************
*
* @functype:
* SVG_Lib_Init_Func
*
* @description:
* A callback that is called when the first OT-SVG glyph is rendered in
* the lifetime of an @FT_Library object. In a typical implementation,
* one would want to allocate a structure and point the `data_pointer`
* to it and perform any library initializations that might be needed.
*
* @inout:
* data_pointer ::
* The SVG rendering module stores a pointer variable that can be used
* by clients to store any data that needs to be shared across
* different hooks. `data_pointer` is essentially a pointer to that
* pointer such that it can be written to as well as read from.
*
* @return:
* FreeType error code. 0 means success.
*
* @since:
* 2.12
*/
typedef FT_Error
(*SVG_Lib_Init_Func)( FT_Pointer *data_pointer );
/**************************************************************************
*
* @functype:
* SVG_Lib_Free_Func
*
* @description:
* A callback that is called when the `ot-svg` module is being freed.
* It is only called if the init hook was called earlier. This means
* that neither the init nor the free hook is called if no OT-SVG glyph
* is rendered.
*
* In a typical implementation, one would want to free any state
* structure that was allocated in the init hook and perform any
* library-related closure that might be needed.
*
* @inout:
* data_pointer ::
* The SVG rendering module stores a pointer variable that can be used
* by clients to store any data that needs to be shared across
* different hooks. `data_pointer` is essentially a pointer to that
* pointer such that it can be written to as well as read from.
*
* @since:
* 2.12
*/
typedef void
(*SVG_Lib_Free_Func)( FT_Pointer *data_pointer );
/**************************************************************************
*
* @functype:
* SVG_Lib_Render_Func
*
* @description:
* A callback that is called to render an OT-SVG glyph. This callback
* hook is called right after the preset hook @SVG_Lib_Preset_Slot_Func
* has been called with `cache` set to `TRUE`. The data necessary to
* render is available through the handle @FT_SVG_Document, which is set
* in the `other` field of @FT_GlyphSlotRec.
*
* The render hook is expected to render the SVG glyph to the bitmap
* buffer that is allocated already at `slot->bitmap.buffer`. It also
* sets the `num_grays` value as well as `slot->format`.
*
* @input:
* slot ::
* The slot to render.
*
* @inout:
* data_pointer ::
* The SVG rendering module stores a pointer variable that can be used
* by clients to store any data that needs to be shared across
* different hooks. `data_pointer` is essentially a pointer to that
* pointer such that it can be written to as well as read from.
*
* @return:
* FreeType error code. 0 means success.
*
* @since:
* 2.12
*/
typedef FT_Error
(*SVG_Lib_Render_Func)( FT_GlyphSlot slot,
FT_Pointer *data_pointer );
/**************************************************************************
*
* @functype:
* SVG_Lib_Preset_Slot_Func
*
* @description:
* A callback that is called to preset the glyph slot. It is called from
* two places.
*
* 1. When `FT_Load_Glyph` needs to preset the glyph slot.
*
* 2. Right before the `svg` module calls the render callback hook.
*
* When it is the former, the argument `cache` is set to `FALSE`. When
* it is the latter, the argument `cache` is set to `TRUE`. This
* distinction has been made because many calculations that are necessary
* for presetting a glyph slot are the same needed later for the render
* callback hook. Thus, if `cache` is `TRUE`, the hook can _cache_ those
* calculations in a memory block referenced by the state pointer.
*
* This hook is expected to preset the slot by setting parameters such as
* `bitmap_left`, `bitmap_top`, `width`, `rows`, `pitch`, and
* `pixel_mode`. It is also expected to set all the metrics for the slot
* including the vertical advance if it is not already set. Typically,
* fonts have horizontal advances but not vertical ones. If those are
* available, they had already been set, otherwise they have to be
* estimated and set manually. The hook must take into account the
* transformations that have been set, and translate the transformation
* matrices into the SVG coordinate system, as the original matrix is
* intended for the TTF/CFF coordinate system.
*
* @input:
* slot ::
* The glyph slot that has the SVG document loaded.
*
* cache ::
* See description.
*
* @inout:
* data_pointer ::
* The SVG rendering module stores a pointer variable that can be used
* by clients to store any data that needs to be shared across
* different hooks. `data_pointer` is essentially a pointer to that
* pointer such that it can be written to as well as read from.
*
* @return:
* FreeType error code. 0 means success.
*
* @since:
* 2.12
*/
typedef FT_Error
(*SVG_Lib_Preset_Slot_Func)( FT_GlyphSlot slot,
FT_Bool cache,
FT_Pointer *state );
/**************************************************************************
*
* @struct:
* SVG_RendererHooks
*
* @description:
* A structure that stores the four hooks needed to render OT-SVG glyphs
* properly. The structure is publicly used to set the hooks via the
* @svg-hooks driver property.
*
* The behavior of each hook is described in its documentation. One
* thing to note is that the preset hook and the render hook often need
* to do the same operations; therefore, it's better to cache the
* intermediate data in a state structure to avoid calculating it twice.
* For example, in the preset hook one can draw the glyph on a recorder
* surface and later create a bitmap surface from it in the render hook.
*
* All four hooks must be non-NULL.
*
* @fields:
* init_svg ::
* The initialization hook.
*
* free_svg ::
* The cleanup hook.
*
* render_hook ::
* The render hook.
*
* preset_slot ::
* The preset hook.
*
* @since:
* 2.12
*/
typedef struct SVG_RendererHooks_
{
SVG_Lib_Init_Func init_svg;
SVG_Lib_Free_Func free_svg;
SVG_Lib_Render_Func render_svg;
SVG_Lib_Preset_Slot_Func preset_slot;
} SVG_RendererHooks;
/**************************************************************************
*
* @struct:
* FT_SVG_DocumentRec
*
* @description:
* A structure that models one SVG document.
*
* @fields:
* svg_document ::
* A pointer to the SVG document.
*
* svg_document_length ::
* The length of `svg_document`.
*
* metrics ::
* A metrics object storing the size information.
*
* units_per_EM ::
* The size of the EM square.
*
* start_glyph_id ::
* The first glyph ID in the glyph range covered by this document.
*
* end_glyph_id ::
* The last glyph ID in the glyph range covered by this document.
*
* transform ::
* A 2x2 transformation matrix to apply to the glyph while rendering
* it.
*
* delta ::
* The translation to apply to the glyph while rendering.
*
* @note:
* When an @FT_GlyphSlot object `slot` is passed down to a renderer, the
* renderer can only access the `metrics` and `units_per_EM` fields via
* `slot->face`. However, when @FT_Glyph_To_Bitmap sets up a dummy
* object, it has no way to set a `face` object. Thus, metrics
* information and `units_per_EM` (which is necessary for OT-SVG) has to
* be stored separately.
*
* @since:
* 2.12
*/
typedef struct FT_SVG_DocumentRec_
{
FT_Byte* svg_document;
FT_ULong svg_document_length;
FT_Size_Metrics metrics;
FT_UShort units_per_EM;
FT_UShort start_glyph_id;
FT_UShort end_glyph_id;
FT_Matrix transform;
FT_Vector delta;
} FT_SVG_DocumentRec;
/**************************************************************************
*
* @type:
* FT_SVG_Document
*
* @description:
* A handle to an @FT_SVG_DocumentRec object.
*
* @since:
* 2.12
*/
typedef struct FT_SVG_DocumentRec_* FT_SVG_Document;
FT_END_HEADER
#endif /* OTSVG_H_ */
/* END */