[Fix] Support custom font to visualize some languages (e.g. Korean)

[ProtossDragoon]

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Motivation

'san-serif' does not support to visualize Korean character.

Modification

python3 -m mmocr.ocr \
--det-ckpt ... \
--det-config ... \
--recog-ckpt ... \
--recog-config ... \
img_example \
--img-out-dir ...

before:

configs/textrecog/_base_/default_runtime.py

visualizer = dict(
    type='TextRecogLocalVisualizer',
    name='visualizer',
    vis_backends=vis_backends) 

output

/usr/local/lib/python3.8/dist-packages/mmengine/visualization/utils.py:238: UserWarning: Glyph 48373 (\N{HANGUL SYLLABLE BOG}) missing from current font.
  s, (width, height) = canvas.print_to_buffer()
/usr/local/lib/python3.8/dist-packages/mmengine/visualization/utils.py:238: UserWarning: Glyph 54788 (\N{HANGUL SYLLABLE HYEON}) missing from current font.
  s, (width, height) = canvas.print_to_buffer()
/usr/local/lib/python3.8/dist-packages/mmengine/visualization/utils.py:238: UserWarning: Glyph 51456 (\N{HANGUL SYLLABLE JUN}) missing from current font.
  s, (width, height) = canvas.print_to_buffer()
/usr/local/lib/python3.8/dist-packages/mmengine/visualization/utils.py:238: UserWarning: Glyph 48276 (\N{HANGUL SYLLABLE BEOM}) missing from current font.
  s, (width, height) = canvas.print_to_buffer()
/usr/local/lib/python3.8/dist-packages/mmengine/visualization/utils.py:238: UserWarning: Glyph 54868 (\N{HANGUL SYLLABLE HWA}) missing from current font.
  s, (width, height) = canvas.print_to_buffer()
... # skipped

after:

configs/textrecog/_base_/default_runtime.py

visualizer = dict(
    type='TextRecogLocalVisualizer',
    name='visualizer',
    font_families='NanumGothic', # new feature
    vis_backends=vis_backends)

I added self.font_families to BaseLocalVisualizer class.

• KIELocalVisualizer._draw_instances() → KIELocalVisualizer._draw_edge_label() → Visualizer.draw_texts()
• KIELocalVisualizer._draw_instances() → BaseLocalVisualizer.get_labels_image() → Visualizer.draw_texts()
• TextRecogLocalVisualizer._draw_instances() → Visualizer.draw_texts()

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects.
• CLA has been signed and all committers have signed the CLA in this PR.

[Harold-lkk]

Better to pass font_families into the function

def get_labels_image(xxx, font_familyies='sans-serif'):
    self.draw_texts(
        labels, (bboxes[:, :2] + bboxes[:, 2:]) / 2,
        vertical_alignments='center',
        horizontal_alignments='center',
        colors='k',
        font_sizes=font_size,
        font_families=self.font_families)

[ProtossDragoon]

@Harold-lkk

There are other functions that call self.draw_texts();

• _draw_edge_label()
• get_labels_image()

Do you think these function should contains the font_families argument?

[Harold-lkk]

Containing will be better

[gaotongxiao]

Hi, would you polish this PR further?

[ProtossDragoon]

@gaotongxiao Yes, maybe this week :)

[ProtossDragoon]

Initially, I tried to add a font_family argument to the _draw_edge_label() function (@Harold-lkk suggested), but I did not explicitly add that argument to the function because text style related arguments such as font_size exist only in the get_labels_image() function. Let me know if you still think the function _draw_edge_label() needs a font_family argument. I'll add it.