[freetype2] GSoC-2019-moazin 5f2dcad 24/32: Add a `units_per_EM' field.

[Moazin Khatti]

branch: GSoC-2019-moazin
commit 5f2dcadbf20742c6ea7cdcab08c6523c68bd5a85
Author: Moazin Khatti <address@hidden>
Commit: Moazin Khatti <address@hidden>

    Add a `units_per_EM' field.
    
    A field `units_per_EM' is added to `FT_SVG_DocumentRec' and
    `FT_SvgGlyphRec'. This is needed because the renderer needs this
    info to properly scale the SVGs if the viewbox width and height
    differ from `face->units_per_EM'. Face object can't be accessed
    because of the restrictions put by `FT_Glyph_To_Bitmap' thus this
    has to be provided separately just like `metrics'.
---
 include/freetype/ftglyph.h     | 15 +++++++++++++++
 include/freetype/svgrenderer.h | 15 +++++++++++++++
 src/base/ftglyph.c             |  3 +++
 src/sfnt/ttsvg.c               |  1 +
 4 files changed, 34 insertions(+)

diff --git a/include/freetype/ftglyph.h b/include/freetype/ftglyph.h
index eea0f8c..6f8fdb8 100644
--- a/include/freetype/ftglyph.h
+++ b/include/freetype/ftglyph.h
@@ -259,6 +259,20 @@ FT_BEGIN_HEADER
    *
    *   metrics ::
    *     A metrics object storing the size information.
+   *
+   *   units_per_EM ::
+   *     The size of the EM square.
+   *
+   * @note:
+   *   `metrics' and `units_per_EM' might look like repetitions since both
+   *   fields are stored in face objects. However, the Glyph Management API
+   *   requires an `FT_Glyph' to store all the information that completely
+   *   describes a glyph. Outline glyphs are themselves scaled thus they
+   *   don't need this information. However, SVG documents do. The field of
+   *   `units_per_EM' is needed because the SVG is to be scaled in case its
+   *   viewbox size differs from `units_per_EM'. For more info, refer to
+   *   the section `Coordinate Systems and Glyph Metrics' of the OpenType
+   *   SVG specs.
    */
   typedef struct  FT_SvgGlyphRec_
   {
@@ -267,6 +281,7 @@ FT_BEGIN_HEADER
     FT_ULong            svg_document_length;
     FT_UInt             glyph_index;
     FT_Size_Metrics     metrics;
+    FT_UShort           units_per_EM;
     /* TODO: (OT-SVG) Maybe put a transformation matrix here */
   } FT_SvgGlyphRec;
 
diff --git a/include/freetype/svgrenderer.h b/include/freetype/svgrenderer.h
index 27e6155..449a443 100644
--- a/include/freetype/svgrenderer.h
+++ b/include/freetype/svgrenderer.h
@@ -165,6 +165,20 @@ FT_BEGIN_HEADER
    *
    *   metrics ::
    *     A metrics object storing the size information.
+   *
+   *   units_per_EM ::
+   *     The size of the EM square.
+   *
+   * @note:
+   *   `metrics' and `units_per_EM' might look like repetitions since both
+   *   fields are stored in face objects. However, the Glyph Management API
+   *   requires an `FT_Glyph' to store all the information that completely
+   *   describes a glyph. Outline glyphs are themselves scaled thus they
+   *   don't need this information. However, SVG documents do. The field of
+   *   `units_per_EM' is needed because the SVG is to be scaled in case its
+   *   viewbox size differs from `units_per_EM'. For more info, refer to
+   *   the section `Coordinate Systems and Glyph Metrics' of the OpenType
+   *   SVG specs.
    */
 
   typedef struct FT_SVG_DocumentRec_
@@ -172,6 +186,7 @@ FT_BEGIN_HEADER
     FT_Byte*         svg_document;
     FT_ULong         svg_document_length;
     FT_Size_Metrics  metrics;
+    FT_UShort        units_per_EM;
   } FT_SVG_DocumentRec;
 
   /**************************************************************************
diff --git a/src/base/ftglyph.c b/src/base/ftglyph.c
index 0954695..22cf25b 100644
--- a/src/base/ftglyph.c
+++ b/src/base/ftglyph.c
@@ -327,6 +327,7 @@
     glyph->svg_document_length = doc_length;
     glyph->glyph_index         = slot->glyph_index;
     glyph->metrics             = document->metrics;
+    glyph->units_per_EM        = document->units_per_EM;
 
     /* copy the document into glyph */
     FT_MEM_COPY( glyph->svg_document, document->svg_document, doc_length );
@@ -376,6 +377,7 @@
     target->glyph_index         = source->glyph_index;
     target->svg_document_length = source->svg_document_length;
     target->metrics             = source->metrics;
+    target->units_per_EM        = source->units_per_EM;
 
     /* allocate space for the svg document */
     target->svg_document = memory->alloc( memory,
@@ -410,6 +412,7 @@
     document->svg_document        = glyph->svg_document;
     document->svg_document_length = glyph->svg_document_length;
     document->metrics             = glyph->metrics;
+    document->units_per_EM        = glyph->units_per_EM;
     slot->format = FT_GLYPH_FORMAT_SVG;
 
     slot->other = document;
diff --git a/src/sfnt/ttsvg.c b/src/sfnt/ttsvg.c
index d9ad75a..798c907 100644
--- a/src/sfnt/ttsvg.c
+++ b/src/sfnt/ttsvg.c
@@ -232,6 +232,7 @@
     svg_document->svg_document        = doc_list;
     svg_document->svg_document_length = doc_length;
     svg_document->metrics             = glyph->face->size->metrics;
+    svg_document->units_per_EM        = glyph->face->units_per_EM;
 
     glyph->other = svg_document;
     glyph->metrics.horiAdvance *= 
((float)glyph->face->size->metrics.x_ppem)/((float)glyph->face->units_per_EM) * 
64.0;