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Include kerning when outputting pdf strings. #18517

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Merged
merged 1 commit into from
Sep 19, 2020
Merged

Include kerning when outputting pdf strings. #18517

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16 changes: 11 additions & 5 deletions lib/matplotlib/_text_layout.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,15 @@
Text layouting utilities.
"""

import dataclasses

from .ft2font import KERNING_DEFAULT, LOAD_NO_HINTING


LayoutItem = dataclasses.make_dataclass(
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What are dataclasses getting us here that a named tuple would not?

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The thing is not iterable, which avoids accidentally relying on an unpacking API (x, y = ...) which would be a pain to modify (i.e. you can't add another field while maintaining a sensible deprecation).
Of course this is private API so in a sense we could do whatever we want, but as a general rule I think dataclasses are nicer (but note that I went for the "functional" declaration API because I certainly wouldn't want to be the person introducing type hints in the codebase :))

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That is a compelling agreement 👍 .

"LayoutItem", ["char", "glyph_idx", "x", "prev_kern"])


def layout(string, font, *, kern_mode=KERNING_DEFAULT):
"""
Render *string* with *font*. For each character in *string*, yield a
Expand All @@ -26,13 +32,13 @@ def layout(string, font, *, kern_mode=KERNING_DEFAULT):
x_position : float
"""
x = 0
last_glyph_idx = None
prev_glyph_idx = None
for char in string:
glyph_idx = font.get_char_index(ord(char))
kern = (font.get_kerning(last_glyph_idx, glyph_idx, kern_mode)
if last_glyph_idx is not None else 0) / 64
kern = (font.get_kerning(prev_glyph_idx, glyph_idx, kern_mode) / 64
if prev_glyph_idx is not None else 0.)
x += kern
glyph = font.load_glyph(glyph_idx, flags=LOAD_NO_HINTING)
yield glyph_idx, x
yield LayoutItem(char, glyph_idx, x, kern)
x += glyph.linearHoriAdvance / 65536
last_glyph_idx = glyph_idx
prev_glyph_idx = glyph_idx
41 changes: 24 additions & 17 deletions lib/matplotlib/backends/backend_pdf.py
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Expand Up @@ -2281,21 +2281,23 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
# complication is avoided, but of course, those fonts can not be
# subsetted.)
else:
singlebyte_chunks = [] # List of (start_x, list-of-1-byte-chars).
multibyte_glyphs = [] # List of (start_x, glyph_index).
prev_was_singlebyte = False
for char, (glyph_idx, glyph_x) in zip(
s,
_text_layout.layout(s, font, kern_mode=KERNING_UNFITTED)):
if ord(char) <= 255:
if prev_was_singlebyte:
singlebyte_chunks[-1][1].append(char)
else:
singlebyte_chunks.append((glyph_x, [char]))
prev_was_singlebyte = True
# List of (start_x, [prev_kern, char, char, ...]), w/o zero kerns.
singlebyte_chunks = []
# List of (start_x, glyph_index).
multibyte_glyphs = []
prev_was_multibyte = True
for item in _text_layout.layout(
s, font, kern_mode=KERNING_UNFITTED):
if ord(item.char) <= 255:
if prev_was_multibyte:
singlebyte_chunks.append((item.x, []))
if item.prev_kern:
singlebyte_chunks[-1][1].append(item.prev_kern)
singlebyte_chunks[-1][1].append(item.char)
prev_was_multibyte = False
else:
multibyte_glyphs.append((glyph_x, glyph_idx))
prev_was_singlebyte = False
multibyte_glyphs.append((item.x, item.glyph_idx))
prev_was_multibyte = True
# Do the rotation and global translation as a single matrix
# concatenation up front
self.file.output(Op.gsave)
Expand All @@ -2307,10 +2309,15 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
self.file.output(Op.begin_text,
self.file.fontName(prop), fontsize, Op.selectfont)
prev_start_x = 0
for start_x, chars in singlebyte_chunks:
for start_x, kerns_or_chars in singlebyte_chunks:
self._setup_textpos(start_x, 0, 0, prev_start_x, 0, 0)
self.file.output(self.encode_string(''.join(chars), fonttype),
Op.show)
self.file.output(
# See pdf spec "Text space details" for the 1000/fontsize
# (aka. 1000/T_fs) factor.
[-1000 * next(group) / fontsize if tp == float # a kern
else self.encode_string("".join(group), fonttype)
for tp, group in itertools.groupby(kerns_or_chars, type)],
Op.showkern)
prev_start_x = start_x
self.file.output(Op.end_text)
# Then emit all the multibyte characters, one at a time.
Expand Down
5 changes: 3 additions & 2 deletions lib/matplotlib/backends/backend_ps.py
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Expand Up @@ -585,8 +585,9 @@ def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
self.set_font(ps_name, prop.get_size_in_points())

thetext = '\n'.join(
'%f 0 m /%s glyphshow' % (x, font.get_glyph_name(glyph_idx))
for glyph_idx, x in _text_layout.layout(s, font))
'{:f} 0 m /{:s} glyphshow'
.format(item.x, font.get_glyph_name(item.glyph_idx))
for item in _text_layout.layout(s, font))
self._pswriter.write(f"""\
gsave
{x:f} {y:f} translate
Expand Down
Binary file added lib/matplotlib/tests/baseline_images/test_backend_pdf/kerning.pdf
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Binary file not shown.
8 changes: 8 additions & 0 deletions lib/matplotlib/tests/test_backend_pdf.py
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Expand Up @@ -271,3 +271,11 @@ def test_empty_rasterized():
fig, ax = plt.subplots()
ax.plot([], [], rasterized=True)
fig.savefig(io.BytesIO(), format="pdf")


@image_comparison(['kerning.pdf'])
def test_kerning():
fig = plt.figure()
s = "AVAVAVAVAVAVAVAV€AAVV"
fig.text(0, .25, s, size=5)
fig.text(0, .75, s, size=20)
6 changes: 3 additions & 3 deletions lib/matplotlib/textpath.py
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Expand Up @@ -149,10 +149,10 @@ def get_glyphs_with_font(self, font, s, glyph_map=None,

xpositions = []
glyph_ids = []
for char, (_, x) in zip(s, _text_layout.layout(s, font)):
char_id = self._get_char_id(font, ord(char))
for item in _text_layout.layout(s, font):
char_id = self._get_char_id(font, ord(item.char))
glyph_ids.append(char_id)
xpositions.append(x)
xpositions.append(item.x)
if char_id not in glyph_map:
glyph_map_new[char_id] = font.get_path()

Expand Down