Issue 4909/1: Add procedure `ly:get-cff-offset`

This commit adds procedure `ly:get-cff-offset`
which gets the offset of 'CFF' table for a font.

1 files changed, 159 insertions, 0 deletions

diff --git a/lily/open-type-font-scheme.cc b/lily/open-type-font-scheme.cc
index 2797ac3e9e..d69d41d8ee 100644
--- a/lily/open-type-font-scheme.cc
+++ b/lily/open-type-font-scheme.cc
@@ -17,6 +17,7 @@
   along with LilyPond.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <cstdio>
 #include "international.hh"
 #include "modified-font-metric.hh"
 #include "open-type-font.hh"
@@ -218,3 +219,161 @@ LY_DEFINE (ly_has_glyph_names_p, "ly:has-glyph-names?",
 
   return has_glyph_names ? SCM_BOOL_T : SCM_BOOL_F;
 }
+
+LY_DEFINE (ly_get_cff_offset, "ly:get-cff-offset",
+           1, 1, 0, (SCM font_file_name, SCM idx),
+           "Get the offset of 'CFF' table for @var{font_file_name},"
+           " returning it as an integer.  The optional"
+           " @var{idx} argument is useful for"
+           " OpenType/CFF collections (OTC) only;"
+           " it specifies the font index within the OTC."
+           "  The default value of @var{idx} is@tie{}0.")
+{
+  LY_ASSERT_TYPE (scm_is_string, font_file_name, 1);
+
+  int i = 0;
+  if (!SCM_UNBNDP (idx))
+    {
+      LY_ASSERT_TYPE (scm_is_integer, idx, 2);
+      i = scm_to_int (idx);
+      if (i < 0)
+        {
+          warning (_ ("font index must be non-negative, using index 0"));
+          i = 0;
+        }
+    }
+
+  string file_name = ly_scm2string (font_file_name);
+
+  FILE *fp = fopen (file_name.c_str (), "rb");
+  if (!fp)
+    {
+      warning (_f ("cannot open font filename `%s'", file_name.c_str ()));
+      return SCM_BOOL_F;
+    }
+
+  char buff[4];
+
+  // Read `sfnt version` (for OTF) or `TTCTag` (for OTC)
+  if (fread (buff, 4, 1, fp) != 1)
+    {
+      fclose (fp);
+      warning (_f ("cannot read %s of `%s'", "header", file_name.c_str ()));
+      return SCM_BOOL_F;
+    }
+
+  if (buff[0] == 't' && buff[1] == 't' && buff[2] == 'c' && buff[3] == 'f')
+    {
+      // For OTC
+      // Find subfont
+
+      // Skip `Version`
+      fseek (fp, 4, SEEK_CUR);
+
+      // Read `numFonts`
+      if (fread (buff, 4, 1, fp) != 1)
+        {
+          fclose (fp);
+          warning (_f ("cannot read %s of `%s'",
+                       "numFonts", file_name.c_str ()));
+          return SCM_BOOL_F;
+        }
+      int numfonts =
+        static_cast<unsigned char>(buff[0]) << 24 |
+        static_cast<unsigned char>(buff[1]) << 16 |
+        static_cast<unsigned char>(buff[2]) << 8 |
+        static_cast<unsigned char>(buff[3]);
+
+      if ( i > numfonts )
+        {
+          warning (_f ("font index %d too large for font `%s', using index 0",
+                       i, file_name.c_str ()));
+          i = 0;
+        }
+
+      // Read `OffsetTable[i]`
+      if (i)
+        fseek (fp, i * 4, SEEK_CUR);
+      if (fread (buff, 4, 1, fp) != 1)
+        {
+          fclose (fp);
+          warning (_f ("cannot read %s of `%s'",
+                       "OffsetTable", file_name.c_str ()));
+          return SCM_BOOL_F;
+        }
+      unsigned int offset =
+        static_cast<unsigned char>(buff[0]) << 24 |
+        static_cast<unsigned char>(buff[1]) << 16 |
+        static_cast<unsigned char>(buff[2]) << 8 |
+        static_cast<unsigned char>(buff[3]);
+
+      // Seek to subfont and skip `sfnt version`
+      fseek (fp, offset + 4, SEEK_SET);
+    }
+
+  // For OTF or subfont of OTC
+
+  // Read `numTables`
+  if (fread (buff, 2, 1, fp) != 1)
+    {
+      fclose (fp);
+      warning (_f ("cannot read %s of `%s'",
+                   "numTables", file_name.c_str ()));
+      return SCM_BOOL_F;
+    }
+  int numtables =
+    static_cast<unsigned char>(buff[0]) << 8 |
+    static_cast<unsigned char>(buff[1]);
+
+  // Skip `searchRange`, `entrySelector` and `rangeShift`
+  fseek (fp, 6, SEEK_CUR);
+
+  // Read Table Records
+  for (int t = 0; t < numtables; t++)
+    {
+      // Read `tag`
+      if (fread (buff, 4, 1, fp) != 1)
+        {
+          fclose (fp);
+          warning (_f ("cannot read %s of `%s'",
+                       "tag", file_name.c_str ()));
+          return SCM_BOOL_F;
+        }
+
+      if (buff[0] == 'C' && buff[1] == 'F' && buff[2] == 'F' && buff[3] == ' ')
+        {
+          // CFF table is found.
+
+          // Skip `checkSum`
+          fseek (fp, 4, SEEK_CUR);
+
+          // Read `offset`
+          if (fread (buff, 4, 1, fp) != 1)
+            {
+              fclose (fp);
+              warning (_f ("cannot read %s of `%s'",
+                           "CFF offset", file_name.c_str ()));
+              return SCM_BOOL_F;
+            }
+          unsigned int offset =
+            static_cast<unsigned char>(buff[0]) << 24 |
+            static_cast<unsigned char>(buff[1]) << 16 |
+            static_cast<unsigned char>(buff[2]) << 8 |
+            static_cast<unsigned char>(buff[3]);
+
+          // Done
+          fclose (fp);
+          return scm_from_unsigned_integer (offset);
+        }
+
+      // For non-CFF table
+
+      // Skip `checkSum`, `offset` and `length`
+      fseek (fp, 12, SEEK_CUR);
+    }
+
+  fclose (fp);
+  warning (_f ("font `%s' index %d does not have `CFF' table",
+               file_name.c_str (), i));
+  return SCM_BOOL_F;
+}