Fix return value of FT2Font.set_text and add tests for it

`PyArray_SimpleNewFromData` does not copy its input data, and the
`std::vector` is a local variable that disappears after the C++ method
returns.

Author: QuLogic

lib/matplotlib/tests/test_ft2font.py

@@ -706,6 +706,27 @@ def test_ft2font_get_kerning(left, right, unscaled, unfitted, default):
                             ft2font.KERNING_DEFAULT) == default
 
 
+def test_ft2font_set_text():
+    file = fm.findfont('DejaVu Sans')
+    font = ft2font.FT2Font(file, hinting_factor=1, _kerning_factor=0)
+    xys = font.set_text('')
+    np.testing.assert_array_equal(xys, np.empty((0, 2)))
+    assert font.get_width_height() == (0, 0)
+    assert font.get_num_glyphs() == 0
+    assert font.get_descent() == 0
+    assert font.get_bitmap_offset() == (0, 0)
+    # This string uses all the kerning pairs defined for test_ft2font_get_kerning.
+    xys = font.set_text('AADAT.XC-J')
+    np.testing.assert_array_equal(
+        xys,
+        [(0, 0), (512, 0), (1024, 0), (1600, 0), (2112, 0), (2496, 0), (2688, 0),
+         (3200, 0), (3712, 0), (4032, 0)])
+    assert font.get_width_height() == (4288, 768)
+    assert font.get_num_glyphs() == 10
+    assert font.get_descent() == 192
+    assert font.get_bitmap_offset() == (6, 0)
+
+
 @pytest.mark.parametrize('family_name, file_name',
                           [("WenQuanYi Zen Hei",  "wqy-zenhei.ttc"),
                            ("Noto Sans CJK JP", "NotoSansCJK.ttc"),

src/ft2font_wrapper.cpp

@@ -14,7 +14,10 @@ static PyObject *convert_xys_to_array(std::vector<double> &xys)
 {
     npy_intp dims[] = {(npy_intp)xys.size() / 2, 2 };
     if (dims[0] > 0) {
-        return PyArray_SimpleNewFromData(2, dims, NPY_DOUBLE, &xys[0]);
+        auto obj = PyArray_SimpleNew(2, dims, NPY_DOUBLE);
+        auto array = reinterpret_cast<PyArrayObject *>(obj);
+        memcpy(PyArray_DATA(array), xys.data(), PyArray_NBYTES(array));
+        return obj;
     } else {
         return PyArray_SimpleNew(2, dims, NPY_DOUBLE);
     }
@@ -631,7 +634,7 @@ const char *PyFT2Font_set_text__doc__ =
     "*flags* can be a bitwise-or of the LOAD_XXX constants;\n"
     "the default value is LOAD_FORCE_AUTOHINT.\n"
     "You must call this before `.draw_glyphs_to_bitmap`.\n"
-    "A sequence of x,y positions is returned.\n";
+    "A sequence of x,y positions in 26.6 subpixels is returned; divide by 64 for pixels.\n";
 
 static PyObject *PyFT2Font_set_text(PyFT2Font *self, PyObject *args, PyObject *kwds)
 {