[fdsc] Implement the table parsing

Related to https://github.com/harfbuzz/harfbuzz/issues/1337

May used in addition to an API related to STAT.

Lots of Apple fonts have it.

src/Makefile.sources

 # Base and default-included sources and headers
 
 HB_BASE_sources = \
+	hb-aat-fdsc-table.hh \
 	hb-aat-layout-ankr-table.hh \
 	hb-aat-layout-bsln-table.hh \
 	hb-aat-layout-common.hh \

src/hb-aat-fdsc-table.hh

+/*
+ * Copyright © 2018  Ebrahim Byagowi
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ */
+
+#ifndef HB_AAT_FDSC_TABLE_HH
+#define HB_AAT_FDSC_TABLE_HH
+
+#include "hb-aat-layout-common.hh"
+
+/*
+ * fdsc -- Font descriptors
+ * https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6fdsc.html
+ */
+#define HB_AAT_TAG_fdsc HB_TAG('f','d','s','c')
+
+
+namespace AAT {
+
+
+struct GXFontDescriptor
+{
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this));
+  }
+
+  public:
+  Tag		tag;		/* The 4-byte table tag name. */
+  Fixed		value;		/* The value for the descriptor tag. */
+  public:
+  DEFINE_SIZE_STATIC (8);
+};
+
+struct gasp
+{
+  enum { tableTag = HB_AAT_TAG_fdsc };
+
+  enum {
+    Weight	 = HB_TAG ('w','g','h','t'),
+				/* Percent weight relative to regular weight.
+				 * (defaul value: 1.0) */
+    Width 	 = HB_TAG ('w','d','t','h'),
+				/* Percent width relative to regular width.
+				 * (default value: 1.0) */
+    Slant 	 = HB_TAG ('s','l','n','t'),
+				/* Angle of slant in degrees, where positive
+				 * is clockwise from straight up.
+				 * (default value: 0.0) */
+    OpticalSize  = HB_TAG ('o','p','s','z'),
+				/* Point size the font was designed for.
+				 * (default value: 12.0) */
+    NonAlphabetic= HB_TAG ('n','a','l','f')
+				/* These values are treated as integers,
+				 * not fixed32s. 0 means alphabetic, and greater
+				 * integers mean the font is non-alphabetic (e.g. symbols).
+				 * (default value: 0) */
+  };
+
+  inline bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this) &&
+		  descriptors.sanitize (c));
+  }
+
+  protected:
+  Fixed		version;	/* Version number of the font descriptors
+				 * table (0x00010000 for the current version). */
+  LArrayOf<GXFontDescriptor>
+		descriptors;	/* List of tagged-coordinate pairs style descriptors
+				 * that will be included to characterize this font.
+				 * Each descriptor consists of a <tag, value> pair.
+				 * These pairs are located in the gxFontDescriptor
+				 * array that follows. */
+  public:
+  DEFINE_SIZE_ARRAY (8, descriptors);
+};
+
+} /* namespace AAT */
+
+
+#endif /* HB_AAT_FDSC_TABLE_HH */

src/hb-aat-layout.cc

@@ -29,6 +29,7 @@
 
 #include "hb-ot-face.hh"
 #include "hb-aat-layout.hh"
+#include "hb-aat-fdsc-table.hh" // Just so we compile it; unused otherwise.
 #include "hb-aat-layout-ankr-table.hh"
 #include "hb-aat-layout-bsln-table.hh" // Just so we compile it; unused otherwise.
 #include "hb-aat-layout-feat-table.hh"