Code to read features from GSUB/GPOS tables

kitty/core_text.m

@@ -946,6 +946,21 @@ get_variation(CTFace *self) {
     return variation_to_python(src);
 }
 
+static PyObject*
+get_features(CTFace *self, PyObject *a UNUSED) {
+    RAII_PyObject(output, PyFrozenSet_New(NULL)); if (!output) return NULL;
+    RAII_CoreFoundation(CFDataRef, cftable, CTFontCopyTable(self->ct_font, kCTFontTableGSUB, kCTFontTableOptionNoOptions));
+    const uint8_t *table = cftable ? CFDataGetBytePtr(cftable) : NULL;
+    size_t table_len = cftable ? CFDataGetLength(cftable) : 0;
+    if (!read_features_from_font_table(table, table_len, output)) return NULL;
+    RAII_CoreFoundation(CFDataRef, cfpostable, CTFontCopyTable(self->ct_font, kCTFontTableGPOS, kCTFontTableOptionNoOptions));
+    table = cfpostable ? CFDataGetBytePtr(cfpostable) : NULL;
+    table_len = cfpostable ? CFDataGetLength(cfpostable) : 0;
+    if (!read_features_from_font_table(table, table_len, output)) return NULL;
+    Py_INCREF(output); return output;
+}
+
+
 static PyObject*
 get_variable_data(CTFace *self) {
     if (!ensure_name_table(self)) return NULL;
@@ -989,6 +1004,7 @@ static PyMethodDef methods[] = {
     METHODB(display_name, METH_NOARGS),
     METHODB(postscript_name, METH_NOARGS),
     METHODB(get_variable_data, METH_NOARGS),
+    METHODB(get_features, METH_NOARGS),
     METHODB(get_variation, METH_NOARGS),
     METHODB(identify_for_debug, METH_NOARGS),
     METHODB(set_size, METH_VARARGS),

kitty/fast_data_types.pyi

@@ -1,6 +1,6 @@
 import termios
 from ctypes import Array, c_ubyte
-from typing import Any, Callable, Dict, Iterator, List, Literal, NewType, Optional, Tuple, TypedDict, Union, overload
+from typing import Any, Callable, Dict, Iterator, List, Literal, NewType, Optional, Tuple, TypedDict, Union, overload, FrozenSet
 
 from kitty.boss import Boss
 from kitty.fonts import FontFeature, VariableData
@@ -433,6 +433,7 @@ class Face:
     def set_size(self, sz_in_pts: float, dpi_x: float, dpi_y: float) -> None: ...
     def render_sample_text(self, text: str, width: int, height: int, fg_color: int = 0xffffff) -> bytes: ...
     def get_variation(self) -> Optional[Dict[str, float]]: ...
+    def get_features(self) -> FrozenSet[str]: ...
 
 
 class CoreTextFont(TypedDict):
@@ -467,6 +468,7 @@ class CTFace:
     def set_size(self, sz_in_pts: float, dpi_x: float, dpi_y: float) -> None: ...
     def render_sample_text(self, text: str, width: int, height: int, fg_color: int = 0xffffff) -> bytes: ...
     def get_variation(self) -> Optional[Dict[str, float]]: ...
+    def get_features(self) -> FrozenSet[str]: ...
 
 
 def coretext_all_fonts(monospaced_only: bool) -> Tuple[CoreTextFont, ...]:

kitty/font-names.c

@@ -119,6 +119,28 @@ read_name_font_table(const uint8_t *table, size_t table_len) {
 
 }
 
+bool
+read_features_from_font_table(const uint8_t *table, size_t table_len, PyObject *output) {
+    if (table_len < 20) return true;
+    const uint16_t *p = (uint16_t*)table;
+    const uint8_t *limit = table + table_len;
+    uint16_t major_version = next, minor_version = next, script_list_offset = next, feature_list_offset = next;
+    (void)major_version; (void)minor_version; (void)script_list_offset;
+    const uint8_t *feature_list_table = table + feature_list_offset;
+    char tag_buf[5] = {0};
+    if (feature_list_table + 2 >= limit) return true;
+    p = (uint16_t*)feature_list_table;
+    uint16_t feature_count = next;
+    const uint8_t *pos = (uint8_t*)p;
+    for (uint16_t i = 0; i < feature_count && pos + 4 < limit; pos += 6, i++) {
+        memcpy(tag_buf, pos, 4);
+        RAII_PyObject(tag, PyUnicode_FromString(tag_buf));
+        if (!tag) return false;
+        if (PySet_Add(output, tag) != 0) return false;
+    }
+    return true;
+}
+
 bool
 read_STAT_font_table(const uint8_t *table, size_t table_len, PyObject *name_lookup_table, PyObject *output) {
     RAII_PyObject(design_axes, PyTuple_New(0));

kitty/fonts.h

@@ -52,6 +52,8 @@ bool
 read_fvar_font_table(const uint8_t *table, size_t table_len, PyObject *name_lookup_table, PyObject *output);
 bool
 read_STAT_font_table(const uint8_t *table, size_t table_len, PyObject *name_lookup_table, PyObject *output);
+bool
+read_features_from_font_table(const uint8_t *table, size_t table_len, PyObject *output);
 
 static inline void
 right_shift_canvas(pixel *canvas, size_t width, size_t height, size_t amt) {

kitty/fonts/common.py

@@ -470,16 +470,19 @@ def develop(family: str = '') -> None:
     opts = Options()
     opts.font_family = parse_font_spec(family)
     ff = get_font_files(opts)
-    def s(d: Descriptor) -> str:
-        return str(face_from_descriptor(d))
+    def s(name: str, d: Descriptor) -> None:
+        f = face_from_descriptor(d)
+        print(name, str(f))
+        features = f.get_features()
+        print('  Features :', ' '.join(sorted(features)))
 
-    print('Medium     :', s(ff['medium']))
+    s('Medium     :', ff['medium'])
     print()
-    print('Bold       :', s(ff['bold']))
+    s('Bold       :', ff['bold'])
     print()
-    print('Italic     :', s(ff['italic']))
+    s('Italic     :', ff['italic'])
     print()
-    print('Bold-Italic:', s(ff['bi']))
+    s('Bold-Italic:', ff['bi'])
 
 
 if __name__ == '__main__':

kitty/freetype.c

@@ -842,6 +842,31 @@ get_variation(Face *self, PyObject *a UNUSED) {
     Py_INCREF(ans); return ans;
 }
 
+static PyObject*
+get_features(Face *self, PyObject *a UNUSED) {
+    FT_Error err;
+    FT_ULong length = 0;
+    RAII_PyObject(output, PyFrozenSet_New(NULL)); if (!output) return NULL;
+    if ((err = FT_Load_Sfnt_Table(self->face, FT_MAKE_TAG('G', 'S', 'U', 'B'), 0, NULL, &length)) == 0) {
+        RAII_ALLOC(uint8_t, table, malloc(length));
+        if (!table) return PyErr_NoMemory();
+        if ((err = FT_Load_Sfnt_Table(self->face, FT_MAKE_TAG('G', 'S', 'U', 'B'), 0, table, &length))) {
+            set_freetype_error("Failed to load the GSUB table from font with error:", err); return NULL;
+        }
+        if (!read_features_from_font_table(table, length, output)) return NULL;
+    }
+    length = 0;
+    if ((err = FT_Load_Sfnt_Table(self->face, FT_MAKE_TAG('G', 'P', 'O', 'S'), 0, NULL, &length)) == 0) {
+        RAII_ALLOC(uint8_t, table, malloc(length));
+        if (!table) return PyErr_NoMemory();
+        if ((err = FT_Load_Sfnt_Table(self->face, FT_MAKE_TAG('G', 'P', 'O', 'S'), 0, table, &length))) {
+            set_freetype_error("Failed to load the GSUB table from font with error:", err); return NULL;
+        }
+        if (!read_features_from_font_table(table, length, output)) return NULL;
+    }
+    Py_INCREF(output); return output;
+}
+
 static PyObject*
 get_variable_data(Face *self, PyObject *a UNUSED) {
     if (!ensure_name_table(self)) return NULL;
@@ -992,6 +1017,7 @@ static PyMethodDef methods[] = {
     METHODB(identify_for_debug, METH_NOARGS),
     METHODB(extra_data, METH_NOARGS),
     METHODB(get_variable_data, METH_NOARGS),
+    METHODB(get_features, METH_NOARGS),
     METHODB(get_variation, METH_NOARGS),
     METHODB(get_best_name, METH_O),
     METHODB(set_size, METH_VARARGS),