raqm_set_language.

Author: anntzer

CHANGELOG.rst

@@ -11,6 +11,7 @@ next
 - Control vector output version with the ``MaxVersion`` special metadata
   entry.
 - Add HARD_LIGHT operator, which was previously missing.
+- Support setting OpenType language tag.
 
 v0.4 (2021-04-02)
 =================

README.rst

@@ -448,13 +448,17 @@ faces in a single file), the *n*\th font (*n*\≥0) can be selected by appending
 
 OpenType font features can be selected by appending ``|feature,...``
 to the filename, followed by a `HarfBuzz feature string`_ (e.g.,
-``"/path/to/font.otf|frac,onum"``); see `examples/opentype_features.py`_.
+``"/path/to/font.otf|frac,onum"``); see `examples/opentype_features.py`_.  A
+language_ tag can likewise be set with ``|language=...``; currently, this
+always applies to the whole buffer, but a PR adding support for slicing syntax
+(similar to font features) would be considered.
 
 .. _HarfBuzz feature string: https://harfbuzz.github.io/harfbuzz-hb-common.html#hb-feature-from-string
+.. _language: https://host-oman.github.io/libraqm/raqm-Raqm.html#raqm-set-language
 
-The syntaxes for selecting TTC subfonts and OpenType font features are
-**experimental** and may change, especially if such features are implemented in
-Matplotlib itself.
+The syntaxes for selecting TTC subfonts and OpenType font features and language
+tags are **experimental** and may change, especially if such features are
+implemented in Matplotlib itself.
 
 Color fonts (e.g. emojis) are handled.
 

src/_raqm.h

@@ -13,6 +13,7 @@ extern "C" {  // Support raqm<=0.2.
   _(get_glyphs) \
   _(layout) \
   _(set_freetype_face) \
+  _(set_language) \
   _(set_text_utf8) \
   _(version_string) \
   _(version_atleast)

src/_util.cpp

@@ -797,7 +797,13 @@ GlyphsAndClusters text_to_glyphs_and_clusters(cairo_t* cr, std::string s)
          *static_cast<std::vector<std::string>*>(
            cairo_font_face_get_user_data(
              cairo_get_font_face(cr), &detail::FEATURES_KEY))) {
-      TRUE_CHECK(raqm::add_font_feature, rq, feature.c_str(), -1);
+      auto lang_tag = "language="s;
+      if (feature.substr(0, lang_tag.size()) == lang_tag) {
+        TRUE_CHECK(raqm::set_language,
+                   rq, feature.c_str() + lang_tag.size(), 0, s.size());
+      } else {
+        TRUE_CHECK(raqm::add_font_feature, rq, feature.c_str(), -1);
+      }
     }
     TRUE_CHECK(raqm::layout, rq);
     auto num_glyphs = size_t{};