More documentation on handling OT-SVG.
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Werner Lemberg
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docs/CHANGES
17
docs/CHANGES
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CHANGES BETWEEN 2.11.1 and 2.12.0
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I. IMPORTANT CHANGES
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- FreeType now handles OT-SVG fonts, to be controlled with
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`FT_CONFIG_OPTION_SVG` configuration macro. By default, it can
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only load the 'SVG ' table of an OpenType font. However, by using
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the `svg-hooks` property of the new 'ot-svg' module it is possible
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to register an external SVG rendering engine. The FreeType demo
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programs have been set up to use 'librsvg' as the rendering
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library.
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This work was Moazin Kathri's GSoC 2019 project.
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======================================================================
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CHANGES BETWEEN 2.11.0 and 2.11.1
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I. IMPORTANT CHANGES
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@ -62,6 +62,7 @@
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* cid_fonts
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* pfr_fonts
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* winfnt_fonts
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* svg_fonts
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* font_formats
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* gasp_table
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*
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@ -82,6 +83,7 @@
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* t1_cid_driver
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* tt_driver
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* pcf_driver
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* ot_svg_driver
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* properties
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* parameter_tags
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* lcd_rendering
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@ -212,16 +212,14 @@ FT_BEGIN_HEADER
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* @description:
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* While FreeType's TrueType driver doesn't expose API functions by
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* itself, it is possible to control its behaviour with @FT_Property_Set
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* and @FT_Property_Get. The following lists the available properties
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* together with the necessary macros and structures.
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* and @FT_Property_Get.
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*
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* The TrueType driver's module name is 'truetype'.
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* The TrueType driver's module name is 'truetype'; a single property
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* @interpreter-version is available, as documented in the @properties
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* section.
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*
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* A single property @interpreter-version is available, as documented in
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* the @properties section.
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*
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* We start with a list of definitions, kindly provided by Greg
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* Hitchcock.
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* To help understand the differences between interpreter versions, we
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* introduce a list of definitions, kindly provided by Greg Hitchcock.
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*
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* _Bi-Level Rendering_
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*
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@ -300,6 +298,31 @@ FT_BEGIN_HEADER
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*/
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/**************************************************************************
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*
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* @section:
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* ot_svg_driver
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*
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* @title:
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* The SVG driver
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*
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* @abstract:
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* Controlling the external rendering of OT-SVG glyphs.
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*
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* @description:
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* By default, FreeType can only load the 'SVG~' table of OpenType fonts
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* if configuration macro `FT_CONFIG_OPTION_SVG` is defined. To make it
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* render SVG glyphs, an external SVG rendering library is needed. All
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* details on the interface between FreeType and the external library
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* via function hooks can be found in section @svg_fonts.
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*
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* The OT-SVG driver's module name is 'ot-svg'; it supports a single
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* property called @svg-hooks, documented below in the @properties
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* section.
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*
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*/
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/**************************************************************************
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*
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* @section:
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@ -798,6 +821,40 @@ FT_BEGIN_HEADER
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*/
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/**************************************************************************
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*
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* @property:
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* svg-hooks
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*
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* @description:
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* Set up the interface between FreeType and an extern SVG rendering
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* library like 'librsvg'. All details on the function hooks can be
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* found in section @svg_fonts.
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*
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* @example:
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* The following example code expects that the four hook functions
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* `svg_*` are defined elsewhere. Error handling is omitted, too.
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*
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* ```
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* FT_Library library;
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* SVG_RendererHooks hooks = {
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* (SVG_Lib_Init_Func)svg_init,
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* (SVG_Lib_Free_Func)svg_free,
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* (SVG_Lib_Render_Func)svg_render,
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* (SVG_Lib_Preset_Slot_Func)svg_preset_slot };
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "ot-svg",
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* "svg-hooks", &hooks );
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* ```
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*
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* @since:
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* 2.12
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*/
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/**************************************************************************
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*
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* @property:
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@ -31,6 +31,29 @@
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FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @section:
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* svg_fonts
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*
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* @title:
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* OpenType SVG Fonts
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*
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* @abstract:
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* OT-SVG API between FreeType and an external SVG rendering library.
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*
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* @description:
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* This section describes the four hooks necessary to render SVG
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* 'documents' that are contained in an OpenType font's 'SVG~' table.
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*
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* For more information on the implementation, see our standard hooks
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* based on 'librsvg' in the [FreeType Demo
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* Programs](https://gitlab.freedesktop.org/freetype/freetype-demos)
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* repository.
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*
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*/
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/**************************************************************************
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*
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* @functype:
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@ -42,9 +65,6 @@ FT_BEGIN_HEADER
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* one would want to allocate a structure and point the `data_pointer`
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* to it and perform any library initializations that might be needed.
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*
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* For more information on the implementation, see our standard hooks
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* based on Librsvg in the 'FreeType Demo Programs' repository.
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*
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* @inout:
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* data_pointer ::
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* The SVG rendering module stores a pointer variable that can be used
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@ -77,9 +97,6 @@ FT_BEGIN_HEADER
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* structure that was allocated in the init hook and perform any
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* library-related closure that might be needed.
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*
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* For more information on the implementation, see our standard hooks
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* based on Librsvg in the 'FreeType Demo Programs' repository.
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*
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* @inout:
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* data_pointer ::
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* The SVG rendering module stores a pointer variable that can be used
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@ -101,7 +118,7 @@ FT_BEGIN_HEADER
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*
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* @description:
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* A callback that is called to render an OT-SVG glyph. This callback
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* hook is called right after the preset hook @SVG_Lib_Preset_SlotFunc
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* hook is called right after the preset hook @SVG_Lib_Preset_Slot_Func
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* has been called with `cache` set to `TRUE`. The data necessary to
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* render is available through the handle @FT_SVG_Document, which is set
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* in the `other` field of @FT_GlyphSlotRec.
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@ -110,9 +127,6 @@ FT_BEGIN_HEADER
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* buffer that is allocated already at `slot->bitmap.buffer`. It also
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* sets the `num_grays` value as well as `slot->format`.
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*
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* For more information on the implementation, see our standard hooks
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* based on Librsvg in the 'FreeType Demo Programs' repository.
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*
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* @input:
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* slot ::
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* The slot to render.
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@ -145,6 +159,7 @@ FT_BEGIN_HEADER
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* two places.
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*
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* 1. When `FT_Load_Glyph` needs to preset the glyph slot.
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*
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* 2. Right before the `svg` module calls the render callback hook.
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*
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* When it is the former, the argument `cache` is set to `FALSE`. When
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@ -165,9 +180,6 @@ FT_BEGIN_HEADER
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* matrices into the SVG coordinate system, as the original matrix is
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* intended for the TTF/CFF coordinate system.
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*
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* For more information on the implementation, see our standard hooks
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* based on Librsvg in the 'FreeType Demo Programs' repository.
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*
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* @input:
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* slot ::
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* The glyph slot that has the SVG document loaded.
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@ -201,8 +213,8 @@ FT_BEGIN_HEADER
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*
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* @description:
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* A structure that stores the four hooks needed to render OT-SVG glyphs
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* properly. The structure is publicly used to set the hooks via driver
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* properties.
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* properly. The structure is publicly used to set the hooks via the
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* @svg-hooks driver property.
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*
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* The behavior of each hook is described in its documentation. One
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* thing to note is that the preset hook and the render hook often need
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@ -211,9 +223,6 @@ FT_BEGIN_HEADER
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* For example, in the preset hook one can draw the glyph on a recorder
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* surface and later create a bitmap surface from it in the render hook.
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*
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* For more information on the implementation, see our standard hooks
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* based on Librsvg in the 'FreeType Demo Programs' repository.
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*
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* @fields:
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* init_svg ::
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* The initialization hook.
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@ -244,7 +253,7 @@ FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @struct:
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* FT_SVG_DocumentRec_
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* FT_SVG_DocumentRec
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*
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* @description:
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* A structure that models one SVG document.
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@ -276,12 +285,12 @@ FT_BEGIN_HEADER
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* The translation to apply to the glyph while rendering.
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*
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* @note:
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* When the slot is passed down to a renderer, the renderer can only
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* access the `metrics` and `units_per_EM` fields via `slot->face`.
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* However, when `FT_Glyph_To_Bitmap` sets up a dummy object, it has no
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* way to set a `face` object. Thus, metrics information and
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* `units_per_EM` (which is necessary for OT-SVG) has to be stored
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* separately.
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* When an @FT_GlyphSlot object `slot` is passed down to a renderer, the
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* renderer can only access the `metrics` and `units_per_EM` fields via
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* `slot->face`. However, when @FT_Glyph_To_Bitmap sets up a dummy
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* object, it has no way to set a `face` object. Thus, metrics
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* information and `units_per_EM` (which is necessary for OT-SVG) has to
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* be stored separately.
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*
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* @since:
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* 2.12
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