Improve warning for unsupported scripts.

anntzer · anntzer · commit b135cbf4c506 · 2021-05-01T12:45:34.000+02:00
Trying e.g. to use an Indic script now gives
```
&lt;string&gt;:5: UserWarning: Glyph 3520 (\N{SINHALA LETTER VAYANNA}) missing from current font.
&lt;string&gt;:5: UserWarning: Matplotlib currently does not support Sinhala natively.
```
diff --git a/lib/matplotlib/_text_helpers.py b/lib/matplotlib/_text_helpers.py
@@ -4,13 +4,37 @@
 
 import dataclasses
 
+from . import _api
 from .ft2font import KERNING_DEFAULT, LOAD_NO_HINTING
 
 
 LayoutItem = dataclasses.make_dataclass(
     "LayoutItem", ["char", "glyph_idx", "x", "prev_kern"])
 
 
+def warn_on_missing_glyph(codepoint):
+    _api.warn_external(
+        "Glyph {} ({}) missing from current font.".format(
+            codepoint,
+            chr(codepoint).encode("ascii", "namereplace").decode("ascii")))
+    block = ("Hebrew" if 0x0590 <= codepoint <= 0x05ff else
+             "Arabic" if 0x0600 <= codepoint <= 0x06ff else
+             "Devanagari" if 0x0900 <= codepoint <= 0x097f else
+             "Bengali" if 0x0980 <= codepoint <= 0x09ff else
+             "Gurmukhi" if 0x0a00 <= codepoint <= 0x0a7f else
+             "Gujarati" if 0x0a80 <= codepoint <= 0x0aff else
+             "Oriya" if 0x0b00 <= codepoint <= 0x0b7f else
+             "Tamil" if 0x0b80 <= codepoint <= 0x0bff else
+             "Telugu" if 0x0c00 <= codepoint <= 0x0c7f else
+             "Kannada" if 0x0c80 <= codepoint <= 0x0cff else
+             "Malayalam" if 0x0d00 <= codepoint <= 0x0d7f else
+             "Sinhala" if 0x0d80 <= codepoint <= 0x0dff else
+             None)
+    if block:
+        _api.warn_external(
+            f"Matplotlib currently does not support {block} natively.")
+
+
 def layout(string, font, *, kern_mode=KERNING_DEFAULT):
     """
     Render *string* with *font*.  For each character in *string*, yield a
diff --git a/lib/matplotlib/tests/test_text.py b/lib/matplotlib/tests/test_text.py
@@ -720,3 +720,14 @@ def test_invalid_color():
 def test_pdf_kerning():
     plt.figure()
     plt.figtext(0.1, 0.5, "ATATATATATATATATATA", size=30)
+
+
+def test_unsupported_script(recwarn):
+    fig = plt.figure()
+    fig.text(.5, .5, "\N{BENGALI DIGIT ZERO}")
+    fig.canvas.draw()
+    assert all(isinstance(warn.message, UserWarning) for warn in recwarn)
+    assert (
+        [warn.message.args for warn in recwarn] ==
+        [(r"Glyph 2534 (\N{BENGALI DIGIT ZERO}) missing from current font.",),
+         (r"Matplotlib currently does not support Bengali natively.",)])
diff --git a/src/ft2font.cpp b/src/ft2font.cpp
@@ -172,15 +172,21 @@ FT2Image::draw_rect_filled(unsigned long x0, unsigned long y0, unsigned long x1,
 static FT_UInt ft_get_char_index_or_warn(FT_Face face, FT_ULong charcode)
 {
     FT_UInt glyph_index = FT_Get_Char_Index(face, charcode);
-    if (!glyph_index) {
-        PyErr_WarnFormat(NULL, 1, "Glyph %lu missing from current font.", charcode);
-        // Apparently PyErr_WarnFormat returns 0 even if the exception propagates
-        // due to running with -Werror, so check the error flag directly instead.
-        if (PyErr_Occurred()) {
-            throw py::exception();
-        }
+    if (glyph_index) {
+        return glyph_index;
+    }
+    PyObject *text_helpers = NULL, *tmp = NULL;
+    if (!(text_helpers = PyImport_ImportModule("matplotlib._text_helpers")) ||
+        !(tmp = PyObject_CallMethod(text_helpers, "warn_on_missing_glyph", "k", charcode))) {
+        goto exit;
     }
-    return glyph_index;
+exit:
+    Py_XDECREF(text_helpers);
+    Py_XDECREF(tmp);
+    if (PyErr_Occurred()) {
+        throw py::exception();
+    }
+    return 0;
 }
 
 
