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Add IndirectTransform for lazy coordinate resolution#31488

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dikshajangra12918-oss wants to merge 14 commits intomatplotlib:mainfrom
dikshajangra12918-oss:indirect-transform-v2
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Add IndirectTransform for lazy coordinate resolution#31488
dikshajangra12918-oss wants to merge 14 commits intomatplotlib:mainfrom
dikshajangra12918-oss:indirect-transform-v2

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@dikshajangra12918-oss dikshajangra12918-oss commented Apr 11, 2026

PR Summary

While exploring issue #22223, I noticed that the coordinate dispatch logic in '_get_xy_transform()' is tightly coupled inside '_AnnotationBase' class in 'text.py'.

This PR adds 'IndirectTransform' - a new class in 'transforms.py' that wraps a callable and resolves it lazily at draw time.

##How this fixes #22223
Currently, there is no clean way to position an artist relative to multiple other artists combined. The problem is that bounding boxes of artists are not known untill draw time.

'IndirectTransform' solves this by storing a callable (like a lambda) that gets called at draw time - when bounding boxes are finally available. This means you can now do:

tr = IndirectTransform(
    lambda: Bbox.union([
        txt1.get_window_extent(),
        txt2.get_window_extent()
    ])
)
'''
This allows any artist to be positioned relative to the combined bounding box of multiple other artists - which is exactly what #22223 requests.

## What changed
Added IndirectTransform class in lib/matplotlib/transforms.py

## Testing
import matplotlib.transforms as T
bbox = T.Bbox([[0, 0], [1, 1]])
tr = T.IndirectTransform(lambda: bbox)
print(tr._resolve())  # BboxTransformTo(Bbox(...))

## AI Assistance
1. Understand the existing transfrom hierarchy in 'transforms.py'
2. Trace through the 6 cases in '_get_xy_transform()'
3. Draft and refine the initial implementation

dikshajangra12918-oss and others added 8 commits April 14, 2026 22:57
@dikshajangra12918-oss
Fix Annotation arrow not updating after setting patchA
a926a30 
Setting patchA on Annotation.arrow_patch has no visible effect because the arrow position is not recomputed.

This change ensures that the annotation is marked as stale when patchA changes, triggering proper recomputation during rendering.
@dikshajangra12918-oss
Preserve user-set patchA in Annotation.update_positions
92543f9 
Add logic to prevent overriding user-set patchA in update_positions. Fixes issues matplotlib#28316.
@dikshajangra12918-oss
Add test_annotation_patchA_not_overridden function
ac535a1 
Add test to verify that manually set patchA on  annotation arrow is preserved after draw.
@dikshajangra12918-oss
Preserve user-set patchA in update_positions
ae84e01 
Only update patchA internally if user has not manually set it.
Fix indentation and Whitespace in update_positions
c02fcb3
ENH: Add IndirectTransform for lazy coordinate resolution
6902c6f
Fix blank lines in IndirectTransform
9ad21d5
Fix linting errors
0adf520
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dikshajangra12918-oss commented Apr 17, 2026 •
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@jiahao @AdamG I've resolved the rebase conflicts, fixed linting errors, and added the IndirectTransforms.pyi.
The PR is ready for review!

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dikshajangra12918-oss commented Apr 23, 2026

Hii @lebigot @xuanxu @jiahao @AdamG,

All checks are passing now - any feedback on the implementation would be really helpful!

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rcomer commented Apr 25, 2026

I suggest this is put on hold until @dikshajangra12918-oss's other PR #31547 is resolved. There is clearly some confusion there and I do not think it will be helped by trying to work on two PRs at once.

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dikshajangra12918-oss commented Apr 25, 2026 •
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I suggest this is put on hold until @dikshajangra12918-oss's other PR #31547 is resolved. There is clearly some confusion there and I do not think it will be helped by trying to work on two PRs at once.

Okay sir.
But actually I finished this PR then started #31547.

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story645 commented Apr 28, 2026 •
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But actually I finished this PR then started #31547.

#31547 is conceptually much much simpler, so one of the things we're trying to gauge is how well you understand what you're doing and how responsive you are to feedback before we invest time on this PR, which is much more work to review.

Also I'm putting this PR into draft b/c it's missing tests and therefore very much not ready for review. (And the unrelated patch stuff should not be here either).

@story645 story645 marked this pull request as draft April 28, 2026 15:21
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dikshajangra12918-oss commented Apr 28, 2026

But actually I finished this PR then started #31547.

#31547 is conceptually much much simpler, so one of the things we're trying to gauge is how well you understand what you're doing and how responsive you are to feedback before we invest time on this PR, which is much more work to review.

Also I'm putting this PR into draft b/c it's missing tests and therefore very much not ready for review. (And the unrelated patch stuff should not be here either).

Thankyou for the feedback!

I understand - I will focus on resolving #31547 first. For this PR, I will add the missing tests and remove the unrelated patch changes before marking it ready for review.

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[ENH]: Position artists (particularly Annotations) relative to multiple other artists

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