Add info on bytecode interpreter versions of Windows.
Provided by Greg Hitchcock.
diff --git a/include/ftttdrv.h b/include/ftttdrv.h
index 8d9c16c..70ad3d5 100644
--- a/include/ftttdrv.h
+++ b/include/ftttdrv.h
@@ -134,6 +134,26 @@
* FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an
* `FT_Err_Unimplemented_Feature' error.
*
+ * Depending on the graphics framework, Microsoft uses different
+ * bytecode engines. As a consequence, the version numbers returned by
+ * a call to the `GETINFO[1]' bytecode instruction are more convoluted
+ * than desired.
+ *
+ * {
+ * framework Windows version result of GETINFO[1]
+ * ----------------------------------------------------
+ * GDI before XP 35
+ * GDI XP and later 37
+ * GDI+ old before Vista 37
+ * GDI+ old Vista, 7 38
+ * GDI+ after 7 40
+ * DWrite before 8 39
+ * DWrite 8 and later 40
+ * }
+ *
+ * Since FreeType doesn't provide all capabilities of DWrite ClearType,
+ * using version~38 seems justified.
+ *
*/
#define TT_INTERPRETER_VERSION_35 35
#define TT_INTERPRETER_VERSION_38 38
