feat: Add Gauge Chart

[glemartret]

Updated code from #1424 (credits to @FlorianArnould)

The implementation of the gauge chart (discussed here #199)

[imaNNeo]

Can you please rebase the branch?

[glemartret]

It should be OK, I also removed files not concerned by this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.98%. Comparing base (15562ee) to head (5db8e81).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1933      +/-   ##
==========================================
+ Coverage   93.07%   93.98%   +0.90%     
==========================================
  Files          50       54       +4     
  Lines        3956     4553     +597     
==========================================
+ Hits         3682     4279     +597     
  Misses        274      274              

Flag	Coverage Δ
flutter	93.98% <100.00%> (+0.90%)	⬆️

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[imaNNeo]

Okay, now I found a little bit of time to take a look at this one. Here I have some concerns, please have a look:

I tried to pass only one color to the VariableGaugeColor, it crashed, and after more investigation, I realized we also have a SimpleGaugeColor
So I think we can just have a single class (no abstraction) for this case and if the colors list has only one color, it's a simple drawing color, but if it has multiple colors, it is a variable color. So we can calculate the limits under the hood by dividing the whole space by the number of colors. Or user can provide a custom limits property with the customized numbers. In this way, we should throw an exception if the limits length is not equals to the colors length. (Just like other places that we have gradients and stops)

valueColor: VariableGaugeColor(
  colors: [
    AppColors.contentColorYellow,
  ],
  limits: [],
),

Or if you want to keep the abstraction, please let me know what other types of GaugeColor we can have?
(In this case, I still think that our VariableGaugeColor should be able to work with a single color)

[imaNNeo]

As I see, when we have a VariableGaugeColor, it draws the stop points as a circular indicator.
How can I disable/customize them?
Because in the beginning, I found them odd here.

[imaNNeo]

I also have a suggestion for the startAngle and endAngle properties (because they are difficult to set)
I suggest having something like startDegreeOffset (just like what we have in the PieChart that is 0 by default -> start from right center), then we can have direction that can be clockwise and counter-clockwise (I'm not sure if we already have a data structure for this one or not). Then we can have a sweepAngle or sweepDegrees that determines the lengths of the arc. I think it's more similar to how our PieChart works (because of startDegreeOffset) and I think it is easier to work (from the developer's perspective).

Please let me know your thoughts

[rsnider19]

any updates on this? I'd love to move off of syncfusion

[glemartret]

@imaNNeo I’ve rebased and updated the PR following your feedback.

[imaNNeo]

Hi there, I just wrote some comments.
Please have a look.

As it is a new chart type, I would like to put more time/effort into it to ensure it is future-compatible and that we won't have breaking changes. That's why I'm a bit strict about it.
And just to mention that I have some free time these days. If you think you don't have enough time to put this effort, I can take over and continue your branch. (You already did a lot of things).

Just let me know what works better for you.

[glemartret]

Hey, no problem, I won't be able to work on it at least today, maybe tomorrow or in the week end.
Feel free to update it if you want, I'm not the original author of this new chart type, I've just updated it to work with new version of your package as the original PR wasn't

[imaNNeo]

Alright, so I would like to continue your work and do the final improvement.
Because I have a limited free time now, so I can fully focus on it.

[imaNNeo]

Alright, we're almost done, here are 4 samples that we have created:

Sample1	Sample2
Screen.Recording.2026-04-21.at.13.51.47.mov	Screen.Recording.2026-04-21.at.13.52.38.mov

Sample3	Sample4
Screen.Recording.2026-04-21.at.13.53.12.mov	Screen.Recording.2026-04-21.at.13.56.06.mov

[imaNNeo]

Thanks @glemartret and @FlorianArnould