For rendering OT-SVG glyphs, a new renderer module `ot-svg' is
created. The module holds hooks to an external library which are
used for rendering. The hooks can be set via module properties.
Also enabled bitmap presetting of OT-SVG glyphs at loading stage.
* include/freetype/fterrdef.h: Adds two errors, namely,
`Missing_SVG_Hooks' and `Invalid_SVG_Document'.
* include/freetype/internal/ftobjs.h: Adds `svg_renderer_state' to
`FT_LibraryRec' to let external libraries store state.
* include/freetype/internal/fttrace.h: Adds entry for `ot-svg'.
* modules.cfg: Ditto.
* include/freetype/internal/internal.h: Adds
`FT_INTERNAL_SVG_INTERFACE_H' for `svginterface.h'.
* include/freetype/internal/svginterface.h: Internal header file
to contain the interface of `ot-svg' module. Just exposes the
preset function.
* include/freetype/otsvg.h: Adds functypes for the four hooks and
a structure to hold them.
* src/base/ftobjs.c: (ft_glyphslot_preset_bitmap) Enable proper
presetting of OT-SVG glyphs by using `ot-svg' renderer.
(ft_add_renderer) Set `renderer->render' for `ot-svg' module.
* src/svg/ftsvg.h: Declaration for `ot-svg' module.
* src/svg/ftsvg.c: Module definition of `ot-svg' and its functions.
* src/svg/svg.c: Single source file of `ot-svg' module.
* src/svg/svgtypes.c: Defines `SVG_Renderer'.
* src/svg/rules.mk: Compilation rules for `ot-svg' module.
* src/svg/module.mk: Module definition of `ot-svg'.
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