BUG: Make FastMarching AllTargets stop condition count distinct targets

[hjmjohnson]

Fixes the AllTargets stop condition in FastMarchingUpwindGradientImageFilter, which compared the reached-target count against the raw target-container size and so never triggered when the target list held duplicate indices. Addresses item B24 of #6575.

Root cause & fix

Each index is accepted (reached) at most once, so a target container with duplicate indices could never satisfy reachedCount == containerSize; AllTargets mode therefore never halted and the front marched the whole image.

The filter now computes the number of distinct target indices once in Initialize() (via std::set<IndexType>) and compares the reached count against that. The change is scoped strictly to the AllTargets branch of UpdateNeighbors; SomeTargets/OneTarget behavior is unchanged.

Test

Adds a GoogleTest with a duplicated target index. On the unfixed code GetTargetValue() stays 0 (target never registered / never halts as intended); after the fix it reports the correct arrival time. Fail-before/pass-after was verified locally. Self-contained synthetic image — no ITKTestingData fixture.

[greptile-apps]

Greptile Summary

This PR fixes AllTargets stopping for duplicate fast-marching targets. The main changes are:

• Counts distinct target indices during FastMarchingUpwindGradientImageFilter::Initialize().
• Uses the distinct target count when deciding whether AllTargets has been reached.
• Adds a GoogleTest case for duplicate target entries.
• Registers the new UpwindGradient GoogleTest source in the FastMarching test driver.

Confidence Score: 5/5

Safe to merge with minimal risk.

The change is narrow, initializes the new count on each run, preserves OneTarget and SomeTargets behavior, and includes focused test coverage.

No files require special attention.

T-Rex Logs

What T-Rex did

• T-Rex ran the requested general contract validation.
• T-Rex did not upload local artifact references with the verification run.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
Modules/Filtering/FastMarching/include/itkFastMarchingUpwindGradientImageFilter.h	Adds private storage for the distinct target count used by AllTargets; no functional issues found.
Modules/Filtering/FastMarching/include/itkFastMarchingUpwindGradientImageFilter.hxx	Computes distinct target indices during initialization and uses that count for AllTargets termination; no functional issues found.
Modules/Filtering/FastMarching/test/CMakeLists.txt	Adds the new UpwindGradient GoogleTest source to the FastMarching GTest driver; no issues found.
Modules/Filtering/FastMarching/test/itkFastMarchingUpwindGradientImageFilterGTest.cxx	Adds a synthetic duplicate-target regression test for AllTargets behavior; no issues found.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
participant Caller as Caller
participant Filter as FastMarchingUpwindGradientImageFilter
participant Targets as TargetPoints
participant Reached as ReachedTargetPoints
Caller->>Filter: SetTargetPoints(duplicates)
Caller->>Filter: SetTargetReachedModeToAllTargets()
Caller->>Filter: Update()
Filter->>Filter: Initialize()
Filter->>Targets: iterate target indices
Filter->>Filter: compute m_TotalDistinctTargets
loop accepted front indices
    Filter->>Targets: compare accepted index
    alt target index matched
        Filter->>Reached: InsertElement(distinct reached target)
        Filter->>Filter: compare Size() to m_TotalDistinctTargets
    end
end
Filter-->>Caller: TargetValue and output

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sequenceDiagram
participant Caller as Caller
participant Filter as FastMarchingUpwindGradientImageFilter
participant Targets as TargetPoints
participant Reached as ReachedTargetPoints
Caller->>Filter: SetTargetPoints(duplicates)
Caller->>Filter: SetTargetReachedModeToAllTargets()
Caller->>Filter: Update()
Filter->>Filter: Initialize()
Filter->>Targets: iterate target indices
Filter->>Filter: compute m_TotalDistinctTargets
loop accepted front indices
    Filter->>Targets: compare accepted index
    alt target index matched
        Filter->>Reached: InsertElement(distinct reached target)
        Filter->>Filter: compare Size() to m_TotalDistinctTargets
    end
end
Filter-->>Caller: TargetValue and output

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