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Fix confusion between text height and ascent in metrics calculations. by anntzer · Pull Request #31107 · matplotlib/matplotlib · GitHub

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Fix confusion between text height and ascent in metrics calculations. - #31107

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QuLogic merged 1 commit into
matplotlib:text-overhaulfrom
anntzer:supal
Feb 18, 2026
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Fix confusion between text height and ascent in metrics calculations.#31107
QuLogic merged 1 commit into
matplotlib:text-overhaulfrom
anntzer:supal

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anntzer commented Feb 6, 2026 •
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The text height includes both the ascender and the descender, but the logic in _get_layout is that multiline texts should be treated as having an ascent at least as large as "l" and a descent at least as large as "p" (not a height at least as large as "lp" and a descent at least as large as "p") to prevent lines from bumping into each other (see changes to test_text/test_multiline, where the topmost superscript was close to bumping into the "p" descender previously).

Partial fix for #21653; see #21653 (comment).

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timhoffm reviewed Feb 6, 2026
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Comment thread lib/matplotlib/text.py Outdated
xys = M.transform(offset_layout) - (offsetx, offsety)

return bbox, list(zip(lines, zip(ws, hs), *xys.T)), descent
return bbox, list(zip(lines, wads, *xys.T)), descent

timhoffm Feb 6, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Do we still need to return descent now that we have d in wads?

anntzer Feb 6, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Good catch, it was anyways unused; removed.

timhoffm commented Feb 6, 2026 •
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You need to also update this call:

matplotlib/lib/matplotlib/offsetbox.py

Line 802 in d68c7e3

bbox, info, yd = self._text._get_layout(renderer)

yd is not unused here. You must reconstruct it from wads.

anntzer commented Feb 6, 2026

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Oops, I missed that call site; fixed.

timhoffm commented Feb 6, 2026

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Code looks good. Not checked, but I assume the image comparison failures are from slight text changes? What's the plan to handle them?

QuLogic moved this to Ready for Review in Font and text overhaul Feb 6, 2026
QuLogic added this to the v3.11.0 milestone Feb 6, 2026

QuLogic commented Feb 7, 2026

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I don't see anything obviously wrong in the code so far. This PR targets the text-overhaul branch, so test images can be handled as with all the other text changes.

There are 248 test image failures with this change, but they are a bit inconsistent in how they manifest. For example, in test_axes.py::test_errorbar[png], the log (10^x) ticks all shift up. I'm uncertain whether any of these ticks are supposed to align here with the linear axis in the other Axes but at least the top and bottom one are close, and they went from about 1 pixel lower to 0.5-1 pixel higher. On the other hand, in test_image.py::test_nonuniform_logscale[png] the log ticks all shift down one pixel. Other than the multiline text alignment image in the original post, maybe the legend in the patheffects tests is the most noticeable change.

anntzer commented Feb 7, 2026

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Agreed that it is hard to judge whether most changes (in non-multiline text) are really better or worse, except the patheffect legend (test_patheffect3) which appears clearly better (more vertically centered in the box) to me.

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(it's much easier to see the difference with the builtin triager, though).

tacaswell commented Feb 12, 2026

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My read is that this makes the code match what the comments said it actually did.

timhoffm approved these changes Feb 12, 2026
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Looks good apart from the vauge naming.

Comment thread lib/matplotlib/offsetbox.py Outdated
QuLogic added a commit to QuLogic/matplotlib that referenced this pull request Feb 14, 2026
Update test images for matplotlib#31107 [skip ci]
56328f2

QuLogic commented Feb 14, 2026

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I've pushed the image changes to the text-overhaul-figures branch: QuLogic@56328f2 and rebased this PR, so it should pass now. Feel free to review those images as it's a separate commit with only the relevant changes.

QuLogic commented Feb 14, 2026

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Test failures look like the Mock.call_count thing, for which I'll merge main into the text-overhaul branch. I'm not sure what's up with the docs build yet.

QuLogic mentioned this pull request Feb 14, 2026
Merged
1 of 5 tasks
Fix confusion between text height and ascent in metrics calculations.
60f2310 
The text height includes both the ascender and the descender, but the
logic in _get_layout is that multiline texts should be treated as having
an ascent at least as large as "l" and a descent at least as large as
"p" (not a height at least as large as "lp" and a descent at least as
large as "p") to prevent lines from bumping into each other (see changes
to test_text/test_multiline, where the topmost superscript was close to
bumping into the "p" descender previously).
QuLogic added a commit to QuLogic/matplotlib that referenced this pull request Feb 17, 2026
Update test images for matplotlib#31107 [skip ci]
90d1bf0
QuLogic merged commit dfe4e55 into matplotlib:text-overhaul Feb 18, 2026
33 of 36 checks passed
github-project-automation Bot moved this from Ready for Review to Done in Font and text overhaul Feb 18, 2026
anntzer deleted the supal branch February 18, 2026 06:14
wavebyrd pushed a commit to wavebyrd/matplotlib that referenced this pull request Mar 13, 2026
Merge pull request matplotlib#31107 from anntzer/supal
10a0988 
Fix confusion between text height and ascent in metrics calculations.
QuLogic added a commit to QuLogic/matplotlib that referenced this pull request Apr 10, 2026
Update test images for font/text overhaul
12d2a4d 
This includes images changes for the following pull requests / commits:

* [Fix center of rotation with
  rotation_mode='anchor'](matplotlib#29199)
  (c44db77)
* [Remove ttconv backwards-compatibility
  code](matplotlib#30145)
  (8caff88)
* [Remove kerning_factor from
  tests](matplotlib#29816)
  (7b4d725)
* [Set text hinting to
  defaults](matplotlib#29816)
  (8255ae2)
* [Update FreeType to
  2.13.3](matplotlib#29816)
  (89c054d)
* [Implement text shaping with
  libraqm](matplotlib#30000)
  (b0ded3a,
  9813523)
* [Add language parameter to Text
  objects](matplotlib#29794)
  (7ce8eae)
* [Fix auto-sized glyphs with BaKoMa
  fonts](matplotlib#29936)
  (3ba2c13)
* [pdf: Improve text with characters outside embedded font
  limits](matplotlib#30512)
  (b70fb88,
  6cedcf7)
* [Prepare `CharacterTracker` for advanced font
  features](matplotlib#30608)
  (8274e17,
  70dc388,
  df670cf,
  ed5e074)
* [Add font feature API to
  Text](matplotlib#29695)
  (972a688)
* [Fix spacing in r"$\max
  f$"](matplotlib#30715)
  (4a99a83)
* [Implement libraqm for vector
  outputs](matplotlib#30607)
  (bd17cd4)
* [Drop the FT2Font intermediate
  buffer](matplotlib#30059)
  (9d7d7b4)
* [Rasterize dvi files without
  dvipng](matplotlib#30039)
  (7627118)
* [Update bundled FreeType and HarfBuzz
  libraries](matplotlib#30938)
  (a161658,
  9619bcc)
* [Fix positioning of wide mathtext
  accents](matplotlib#31069)
  (c2fa7ba)
* [Refactor RendererAgg.draw_{mathtext,text,tex} to use same base
  algorithm](matplotlib#31085)
  (931bcf3)
* [Implement TeX's fraction and script
  alignment](matplotlib#31046)
  (94ff452,
  4bfa0f9,
  1cd8510)
* [Fix confusion between text height and ascent in metrics
  calculations](matplotlib#31107)
  (60f2310)
* [mathtext: Fetch quad width & axis height from font
  metrics](matplotlib#31110)
  (692df3f,
  383028b)
* [mathtext: add mathnormal and distinguish between normal and italic
  family](matplotlib#31121)
  (a6913f3)
* [ENH: Ignore empty text for
  tightbbox](matplotlib#31285)
  (d772043)
* [Drop axis_artist tickdir image compat, due to text-overhaul
  merge](matplotlib#31281)
  (2057583)
* [text: Use font metrics to determine line
  heights](matplotlib#31291)
  (3ab6a27,
  d961462,
  97f4943)
* [ps/pdf: Override font height metrics to support AFM
  files](matplotlib#31371)
  (e0913d4)
* [TST: Cleanup back-compat code in tests touched by text
  overhaul](matplotlib#31295)
  (7c33379)
* [TST: Set tests touched by text overhaul to mpl20
  style](matplotlib#31300)
  (41c4d8d)
QuLogic mentioned this pull request Apr 10, 2026
Merged
4 tasks done
anntzer mentioned this pull request Sep 8, 2026
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tacaswell tacaswell approved these changes
timhoffm timhoffm approved these changes

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topic: text

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Font and text overhaul
Status: Done

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v3.11.0

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