fix: keep single-slice pie/donut charts visible after the enter animation

[dmitriy-bty]

Summary

Fixes #97. A pie or donut chart with a single slice (one category making up
100% of the total) animates in correctly but disappears the moment the enter
animation finishes. It is only visible while the animation is still running.

Root cause

AnimatedChartPainter._drawPieAnimated in
lib/src/widgets/animated_chart_painter.dart builds each slice with
Path.arcTo (outer/inner arcs for a donut at lines ~2238 and ~2249, the pie
wedge at line ~2261). The animated sweep angle is:

final sweepAngle = (value / total) * 2 * math.pi;   // line 2169
final animatedSweepAngle = sweepAngle * sliceProgress; // line 2189

For a lone slice, value / total == 1.0, so sweepAngle == 2*pi. At the final
frame sliceProgress == 1.0, making animatedSweepAngle exactly 2*pi.

Path.arcTo draws nothing for a full 2*pi sweep: its start and stop unit
vectors coincide, so the arc collapses to a zero-length segment and the slice
path ends up empty. This is unlike Canvas.drawArc (used elsewhere in this file
for the radial gauges), which special-cases a full-circle sweep to a complete
oval. Mid-animation the sweep is still below 2*pi, which is exactly why the
slice renders during the animation and only vanishes when it completes. The same
happens for a full pie (innerRadius: 0), not just donuts.

Change

In _drawPieAnimated, when animatedSweepAngle reaches a full circle, build the
shape from ovals instead of arcTo:

• Full pie: a single filled circle (addOval).
• Full donut: an even-odd outer/inner oval pair, giving a proper ring.

Partial slices (sweep < 2*pi) keep the existing arcTo path untouched, so
multi-slice pies and donuts render exactly as before. The change is contained to
the slice-path construction; the existing fill, stroke, label, and explode logic
apply to the new path unchanged (fill yields the disc/ring; stroke yields the
circle outline(s), which is the correct outline for a complete pie/ring).

Validation

• Deterministic root-cause trace against the current source (v1.17.6): the only
  code path that can produce a 2*pi arcTo sweep is a slice whose
  value / total == 1.0 at sliceProgress == 1.0; for every partial slice
  animatedSweepAngle < 2*pi, so the branch and its output are unchanged.
• Non-regression reasoning: multi-slice pies never reach the new branch because
  each slice's sweep is strictly less than 2*pi.
• Automated regression test (test/single_slice_pie_test.dart): renders
  AnimatedChartPainter at animationProgress: 1.0 for a one-category (100%)
  dataset and counts the pixels that differ from the background, asserting the
  slice actually fills the disc (pie) and the ring (donut). The failure mode is
  a visually empty fill — the painter still paints, just a zero-area path — so
  the existing findsOneWidget-style tests can't detect it; a pixel check can.
  Confirmed the test fails on the pre-fix arcTo path (~800 non-background
  pixels — the empty full-circle sweep) and passes with this change (~21k–32k
  non-background pixels for the ring / disc), covering the exact regression the
  existing multi-slice pie test misses.
• Full suite green: flutter test — 299/299 passing, including the two new
  cases; no other test affected.

Reproduction

CristalyseChart()
  .data([{'label': 'a', 'value': 1}])
  .mappingPie(value: 'value', category: 'label')
  .geomPie(innerRadius: 26)
  .build();

The donut renders during the animation, then vanishes when it completes on
main; with this change it stays as a full ring. Setting innerRadius: 0
reproduces the same behavior for a full pie.

[vercel]

@dmitriy-bty is attempting to deploy a commit to the DoublOne Team on Vercel.

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[coderabbitai]

Walkthrough

The pie slice path-generation logic in _drawPieAnimated was updated to correctly render slices when animatedSweepAngle reaches or exceeds 2π. It now constructs oval-based paths (addOval, with evenOdd fill for donut rings) instead of relying on arcTo, which previously produced empty paths for full-circle sweeps.

Changes

Full-Circle Pie Slice Rendering Fix

Layer / File(s)	Summary
Full-circle slice path construction lib/src/widgets/animated_chart_painter.dart	Adds a fullCircle constant and checks whether animatedSweepAngle reaches 2π; when it does, builds the slice using addOval (with evenOdd fill for donut inner/outer ovals) instead of arcTo, falling back to the existing donut-slice logic for non-full sweeps.

Estimated code review effort: 2 (Simple) | ~10 minutes

Related issues: Fixes reported bug where single-slice pie/donut charts disappear once the enter animation completes, since arcTo produces an empty path at a full 2π sweep.

Suggested reviewers: rudi-q

🥧 A single slice, spinning ‘round,

Vanished once the anim wound down.

Now ovals drawn with evenOdd care,

Keep the ring forever there.

No more empty, ghostly pie —

Full circles rendered, reaching sky. 🍩

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The change satisfies #97 by handling 2π full-circle slices for both pies and donuts while leaving partial slices unchanged.
Out of Scope Changes check	✅ Passed	The patch stays focused on the requested slice-path fix and introduces no unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Title check	✅ Passed	The title clearly states the key fix: keeping single-slice pie/donut charts visible after enter animation.
Description check	✅ Passed	The description directly explains the bug, root cause, fix, and validation for the same pie/donut animation issue.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@lib/src/widgets/animated_chart_painter.dart`:
- Around line 2203-2223: The full-circle fix in animated_chart_painter.dart
needs regression coverage for the single-slice case. Add a widget test around
AnimatedCristalyseChartWidget that uses a one-point dataset and exercises both
PieGeometry(innerRadius: 0) and a donut inner radius, then pumpAndSettle and
verify the chart still renders/ remains visible. This should specifically cover
the path that now uses the full-circle oval logic instead of the arc path, so
the existing multi-category pie test is not sufficient.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 7a08971f-593d-42d5-94d1-7d243c05ad63

📥 Commits

Reviewing files that changed from the base of the PR and between 8114cf3 and 36f3e5b.

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• lib/src/widgets/animated_chart_painter.dart