Add font_feature_settings

Close #2247

kitty/config.py

@@ -410,6 +410,19 @@ def handle_symbol_map(key, val, ans):
     ans['symbol_map'].update(parse_symbol_map(val))
 
 
+@special_handler
+def handle_font_feature_settings(key, val, ans):
+    parts = val.split(':', maxsplit=2)
+    if len(parts) != 2:
+        if parts[0] == "none":
+            return
+        else:
+            log_error("Ignoring invalid font_feature_settings for font {}".format(parts[0]))
+    else:
+        font, features = parts
+        ans['font_feature_settings'].update({font.strip(): features.strip().split()})
+
+
 @special_handler
 def handle_kitten_alias(key, val, ans):
     parts = val.split(maxsplit=2)
@@ -495,7 +508,7 @@ def option_names_for_completion():
 
 
 def parse_config(lines, check_keys=True, accumulate_bad_lines=None):
-    ans = {'symbol_map': {}, 'keymap': {}, 'sequence_map': {}, 'key_definitions': [], 'env': {}, 'kitten_aliases': {}}
+    ans = {'symbol_map': {}, 'keymap': {}, 'sequence_map': {}, 'key_definitions': [], 'env': {}, 'kitten_aliases': {}, 'font_feature_settings': {}}
     parse_config_base(
         lines,
         defaults,

kitty/config_data.py

@@ -276,6 +276,48 @@ or by defining shortcuts for it in kitty.conf, for example::
     map alt+1 disable_ligatures_in active always
     map alt+2 disable_ligatures_in all never
     map alt+3 disable_ligatures_in tab cursor
+
+Note: If font_feature_settings is enabled, this feature has no effect.
+'''))
+
+o('font_feature_settings', 'none', long_text=_('''
+Choose exactly which OpenType features to enable or disable. This is useful as
+some fonts might have many features worthwhile in a terminal—for example, Fira
+Code Retina includes a discretionary feature, :code:`zero`, which in that font
+changes the appearance of the zero (0), to make it more easily distinguishable
+from Ø. Fira Code Retina also includes other discretionary features known as
+Stylistic Sets which have the tags :code:`ss01` through :code:`ss20`.
+
+Note that this code is indexed by PostScript name, and not TTF name or font
+family; this allows you to define very precise feature settings; e.g. you can
+disable a feature in the italic font but not in the regular font.
+
+Note that this feature ignores the value of :code:`disable_ligatures`, because
+it assumes you want to fine tune exactly which OpenType tags are
+enabled/disabled.  See examples below.
+
+To get the PostScript name for a font, ask Fontconfig for it, using your family
+name:
+
+    $ fc-match "Fira Code" postscriptname
+    :postscriptname=FiraCode-Regular
+    $ fc-match "Fira Code Retina" postscriptname
+    :postscriptname=FiraCode-Retina
+    $ fc-match "TT2020Base:style=italic" postscriptname
+    :postscriptname=TT2020Base-Italic
+
+Enable alternate zero and oldstyle numerals:
+
+    font_feature_settings FiraCode-Retina: +zero +onum
+
+Enable only alternate zero:
+
+    font_feature_settings FiraCode-Retina: +zero
+
+Disable the normal ligatures, but keep the :code:`calt` feature which (in this
+font) breaks up monotony:
+
+    font_feature_settings TT2020StyleB-Regular: -liga +calt
 '''))
 
 

kitty/fonts.c

@@ -62,6 +62,7 @@ static hb_feature_t hb_features[3] = {{0}};
 static char_type shape_buffer[4096] = {0};
 static size_t max_texture_size = 1024, max_array_len = 1024;
 typedef enum { LIGA_FEATURE, DLIG_FEATURE, CALT_FEATURE } HBFeature;
+static PyObject* font_feature_settings = NULL;
 
 typedef struct {
     char_type left, right;
@@ -71,16 +72,16 @@ typedef struct {
 static SymbolMap *symbol_maps = NULL;
 static size_t num_symbol_maps = 0;
 
-
-
 typedef struct {
     PyObject *face;
     // Map glyphs to sprite map co-ords
     SpritePosition sprite_map[1024];
     hb_feature_t hb_features[8];
+    hb_feature_t* ffs_hb_features;
     size_t num_hb_features;
+    size_t num_ffs_hb_features;
     SpecialGlyphCache special_glyph_cache[SPECIAL_GLYPH_CACHE_SIZE];
-    bool bold, italic, emoji_presentation;
+    bool bold, italic, emoji_presentation, ffs_set;
 } Font;
 
 typedef struct {
@@ -363,6 +364,22 @@ init_font(Font *f, PyObject *face, bool bold, bool italic, bool emoji_presentati
         copy_hb_feature(f, LIGA_FEATURE); copy_hb_feature(f, DLIG_FEATURE);
     }
     copy_hb_feature(f, CALT_FEATURE);
+    if (font_feature_settings != NULL){
+        const char* face = postscript_name_for_face(f->face);
+
+        PyObject* o = PyDict_GetItemString(font_feature_settings, face);
+        if (o != NULL) {
+            long len = PyList_Size(o);
+            hb_feature_t* hb_feat = calloc(len, sizeof(hb_feature_t));
+            for (long i = len-1; i >= 0; i--) {
+                PyObject* item = PyList_GetItem(o, i);
+                const char* feat = PyUnicode_AsUTF8(item);
+                hb_feature_from_string(feat, -1, &hb_feat[i]);
+            }
+            f->ffs_hb_features = hb_feat;
+            f->num_ffs_hb_features = len;
+        }
+    }
     return true;
 }
 
@@ -776,6 +793,9 @@ shape(CPUCell *first_cpu_cell, GPUCell *first_gpu_cell, index_type num_cells, hb
     group_state.last_gpu_cell = first_gpu_cell + (num_cells ? num_cells - 1 : 0);
     load_hb_buffer(first_cpu_cell, first_gpu_cell, num_cells);
 
+    if (fobj->num_ffs_hb_features > 0)
+        hb_shape(font, harfbuzz_buffer, fobj->ffs_hb_features, fobj->num_ffs_hb_features);
+    else
         hb_shape(font, harfbuzz_buffer, fobj->hb_features, fobj->num_hb_features - (disable_ligature ? 0 : 1));
 
     unsigned int info_length, positions_length;
@@ -1184,11 +1204,11 @@ static PyObject*
 set_font_data(PyObject UNUSED *m, PyObject *args) {
     PyObject *sm;
     Py_CLEAR(box_drawing_function); Py_CLEAR(prerender_function); Py_CLEAR(descriptor_for_idx);
-    if (!PyArg_ParseTuple(args, "OOOIIIIO!d",
+    if (!PyArg_ParseTuple(args, "OOOIIIIO!dO",
                 &box_drawing_function, &prerender_function, &descriptor_for_idx,
                 &descriptor_indices.bold, &descriptor_indices.italic, &descriptor_indices.bi, &descriptor_indices.num_symbol_fonts,
-                &PyTuple_Type, &sm, &global_state.font_sz_in_pts)) return NULL;
-    Py_INCREF(box_drawing_function); Py_INCREF(prerender_function); Py_INCREF(descriptor_for_idx);
+                &PyTuple_Type, &sm, &global_state.font_sz_in_pts, &font_feature_settings)) return NULL;
+    Py_INCREF(box_drawing_function); Py_INCREF(prerender_function); Py_INCREF(descriptor_for_idx); Py_INCREF(font_feature_settings);
     free_font_groups();
     clear_symbol_maps();
     num_symbol_maps = PyTuple_GET_SIZE(sm);

kitty/fonts/render.py

@@ -103,7 +103,7 @@ def set_font_family(opts=None, override_font_size=None, debug_font_matching=Fals
     set_font_data(
         render_box_drawing, prerender_function, descriptor_for_idx,
         indices['bold'], indices['italic'], indices['bi'], num_symbol_fonts,
-        sm, sz
+        sm, sz, opts['font_feature_settings']
     )