fix(core): re-apply invert after colormap when scrolling a stack

[sedghi]

Context

Regression report: OHIF/Viewers#6153 — "After a reset, Invert is lost when scrolling between slices."

Repro: open a stack study → Invert → Reset → Invert again (the current slice inverts) → scroll to another slice → the invert is gone.

Root cause

Bisected to #2679, which added setColormap(colormap) (and VOILUTFunction/sharpening/smoothing) to StackViewport._setPropertiesFromCache() — the method that runs on every stack scroll.

• _resetProperties() calls setColormap(matchedColormap), so after a Reset this.colormap is defined (before any reset it is undefined).
• Every subsequent scroll then calls setColormap(this.colormap) inside _setPropertiesFromCache, which rebuilds the RGB transfer function in its default, non-inverted state.
• The setInvertColor(invert) that follows is a no-op: setInvertColorGPU only flips the transfer function when the requested value differs from this.invert ((!this.invert && invert) || (this.invert && !invert)), and this.invert still holds the carried-over true. So the freshly rebuilt TF stays non-inverted and the inversion is silently dropped.

This is exactly why the loss appears only after a reset (that's what makes the colormap defined), and only did so after #2679 added the colormap re-application on scroll.

Fix

In _setPropertiesFromCache, clear this.invert right after setColormap(...) so the tracked flag matches the rebuilt (non-inverted) transfer function. The subsequent setInvertColor(invert) — called with the desired value captured before the mutation — then actually re-applies the inversion instead of being skipped by the no-op guard. #2679's colormap preservation is retained.

Testing

• Manual: Invert → Reset → Invert → scroll — inversion now persists across slices.
• Regression checks: Reset still restores defaults; a colormap set by the user still persists across scrolling.

Summary by CodeRabbit

• Bug Fixes
  • Fixed an issue where image inversion could be lost when restoring cached viewport settings, ensuring inversion is correctly reapplied after colormap/transfer function restoration.
  • Added a regression test to confirm inversion remains enabled (and transfer-function colors stay consistent) when switching slices after resetProperties().

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 317f51d0-d3e1-4282-9480-608c636ace29

📥 Commits

Reviewing files that changed from the base of the PR and between 90c1145 and 9aa94cd.

📒 Files selected for processing (1)

• packages/core/test/stackViewport_gpu_render_test.js

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📝 Walkthrough

Walkthrough

StackViewport now resets its tracked inversion state during cache restoration. A GPU test verifies that inversion and RGB transfer-function colors remain consistent after resetProperties() and scrolling to another slice.

Changes

Cached inversion restoration

Layer / File(s)	Summary
Reset inversion tracking during cache restoration packages/core/src/RenderingEngine/StackViewport.ts	Cache restoration clears the tracked inversion flag before applying cached colormap and inversion properties.
Validate inversion continuity after scrolling packages/core/test/stackViewport_gpu_render_test.js	GPU coverage verifies inversion and transfer-function colors remain unchanged after resetting properties and changing the displayed slice.

Estimated code review effort: 2 (Simple) | ~5 minutes

Possibly related PRs

• cornerstonejs/cornerstone3D#2679: Also preserves inversion and colormap state during stack viewport cache restoration and actor re-initialization.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The narrative covers context, root cause, fix, and testing, but the required checklist and tested-environment details are incomplete.	Add the completed checklist items and fill in OS, Node, and browser details; include any missing Changes & Results content if needed.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise, semantic-release style, and accurately summarizes the main fix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/stack-invert-lost-on-scroll

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