Improve and future-proof OTF fonts support in w32uniscribe.c

* src/w32uniscribe.c (uniscribe_otf_capability): Add commentary
about the expected results and why the new Uniscribe APIs are not
used in this function.
(ScriptGetFontScriptTags_Proc, ScriptGetFontLanguageTags_Proc)
(ScriptGetFontFeatureTags_Proc): New function typedefs.
(uniscribe_new_apis): New static variable.
(uniscribe_check_features): New function, implements OTF features
verification while correctly accounting for features in the list
after the nil member, if any.
(uniscribe_check_otf_1): New function, retrieves the features
supported by the font for the requested script and language using
the Uniscribe APIs available from Windows Vista onwards.
(uniscribe_check_otf): If the new Uniscribe APIs are available,
use them in preference to reading the font data directly.  Call
uniscribe_check_features to verify that the requested features are
supported, replacing the original incomplete code.
(syms_of_w32uniscribe): Initialize function pointers for the new
Uniscribe APIs.  (Bug#21260)
(otf_features): Scan the script, langsys, and feature arrays back
to front, so that the result we return has them in alphabetical
order, like ftfont.c does.
* src/w32fns.c (syms_of_w32fns) <w32-disable-new-uniscribe-apis>:
New variable for debugging w32uniscribe.c code.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/w32fns.c b/src/w32fns.c
index 189a27c62f1..e91097ba20e 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -9242,6 +9242,16 @@ Default is nil.
 This variable has effect only on NT family of systems, not on Windows 9X.  */);
   w32_use_fallback_wm_chars_method = 0;
 
+  DEFVAR_BOOL ("w32-disable-new-uniscribe-apis",
+               w32_disable_new_uniscribe_apis,
+               doc: /* Non-nil means don't use new Uniscribe APIs.
+The new APIs are used to access OTF features supported by fonts.
+This is intended only for debugging of the new Uniscribe-related code.
+Default is nil.
+
+This variable has effect only on Windows Vista and later.  */);
+  w32_disable_new_uniscribe_apis = 0;
+
 #if 0 /* TODO: Port to W32 */
   defsubr (&Sx_change_window_property);
   defsubr (&Sx_delete_window_property);