[Feature] Visualize keypoint indexes on the image

[Tau-J]

Motivation

Visualize keypoint indexes on the image.

Modification

BC-breaking (Optional)

Use cases (Optional)

add --show-kpt-idx to image_demo.py, topdown_demo_with_mmdet.py and bottomup_demo.py

For example:

python demo/topdown_demo_with_mmdet.py \
    ${MMDET_CONFIG_FILE} ${MMDET_CHECKPOINT_FILE} \
    ${MMPOSE_CONFIG_FILE} ${MMPOSE_CHECKPOINT_FILE} \
    --input ${INPUT_PATH} \
    --show-kpt-idx \
    --show

The result is as follow:

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 tests to ensure correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[Ben-Louis]

Do you feel that the fontsize=radius*10 is somewhat excessive?

In my opinion, setting the fontsize=radius*3 would make the visualization result looks better:

Besides, using bg color appears to enhance the clarity of the text:

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.04 🎉

Comparison is base (af88d62) 82.15% compared to head (94de007) 82.19%.

❗ Current head 94de007 differs from pull request most recent head 8d89d67. Consider uploading reports for the commit 8d89d67 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #2051      +/-   ##
===========================================
+ Coverage    82.15%   82.19%   +0.04%     
===========================================
  Files          225      225              
  Lines        13373    13375       +2     
  Branches      2268     2269       +1     
===========================================
+ Hits         10986    10994       +8     
+ Misses        1875     1868       -7     
- Partials       512      513       +1     

Flag	Coverage Δ
unittests	82.19% <0.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmpose/visualization/local_visualizer.py	78.14% <0.00%> (-0.87%)	⬇️

... and 2 files with indirect coverage changes

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