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Gang929 fix stacked area series negative #2086

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Merged
beto-rodriguez merged 10 commits into from
Feb 8, 2026
Merged

Gang929 fix stacked area series negative #2086

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53739c4
Merge pull request #1965 from beto-rodriguez/dev
beto-rodriguez Sep 12, 2025
b82ca03
Merge pull request #1975 from beto-rodriguez/dev
beto-rodriguez Sep 13, 2025
f767ca7
Fix stack calculation for positive and negative values
gang929 Feb 4, 2026
3e1498d
Merge branch 'fix-StackedAreaSeries-Negative' of https://github.com/g…
beto-rodriguez Feb 8, 2026
0870b59
Initial plan
Copilot Feb 8, 2026
cc9fa0c
Add regression tests for mixed positive/negative stacked values
Copilot Feb 8, 2026
84742e8
Add detailed comments explaining the test expectations
Copilot Feb 8, 2026
0a57ce5
Address PR review feedback: remove line numbers and use robust point …
Copilot Feb 8, 2026
8d3e614
Enable workflow to run on all branches
Copilot Feb 8, 2026
ac9b8d3
Merge pull request #2087 from Live-Charts/copilot/sub-pr-2086
beto-rodriguez Feb 8, 2026
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1 change: 0 additions & 1 deletion .github/workflows/livecharts.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,6 @@ permissions:

on:
pull_request:
branches: [ master, dev ]

jobs:

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6 changes: 6 additions & 0 deletions src/LiveChartsCore/Kernel/Stacker.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -125,16 +125,22 @@ public double StackPoint(ChartPoint point, int seriesStackPosition)
if (value >= 0)
{
currentStack.End += value;
currentStack.NegativeEnd += value;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;

return positiveTotal;
}
else
{
currentStack.End += value;
currentStack.NegativeEnd += value;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
Comment on lines 127 to +143

Copilot AI Feb 8, 2026

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In the value >= 0 branch, the code now also adds the positive value to currentStack.NegativeEnd and _totals[index].Negative. That mixes the positive and negative stacks/totals; it will shift NegativeEnd upward and make NegativeTotal positive, which breaks later negative stacking (next series uses previousActiveStack.NegativeEnd) and can produce incorrect StackedValue.Share / bounds.

Suggested change
currentStack.End += value;
currentStack.NegativeEnd += value;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;
return positiveTotal;
}
else
{
currentStack.End += value;
currentStack.NegativeEnd += value;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
// positive values contribute only to the positive stack and positive totals
currentStack.End += value;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
return positiveTotal;
}
else
{
// negative values contribute only to the negative stack and negative totals
currentStack.NegativeEnd += value;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;

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Comment on lines 127 to +143

Copilot AI Feb 8, 2026

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In the value < 0 branch, the code now also adds the negative value to currentStack.End and _totals[index].Positive. That contaminates the positive stack baseline (previousActiveStack.End is used as the next series' positiveStart) and can make Total incorrect/negative, affecting stacked rendering and axis bounds.

Suggested change
currentStack.End += value;
currentStack.NegativeEnd += value;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;
return positiveTotal;
}
else
{
currentStack.End += value;
currentStack.NegativeEnd += value;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
// positive values contribute only to the positive stack and total
currentStack.End += value;
var positiveTotal = _totals[index].Positive + value;
_totals[index].Positive = positiveTotal;
return positiveTotal;
}
else
{
// negative values contribute only to the negative stack and total
currentStack.NegativeEnd += value;
var negativeTotal = _totals[index].Negative + value;
_totals[index].Negative = negativeTotal;

Copilot uses AI. Check for mistakes.

return negativeTotal;
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beto-rodriguez marked this conversation as resolved.
}
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84 changes: 84 additions & 0 deletions tests/CoreTests/SeriesTests/StackedAreaSeriesTest.cs
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Expand Up @@ -349,4 +349,88 @@ public void ShouldPlaceDataLabel()

Assert.IsTrue(!chart.CoreCanvas.ContainsPaintTask(previousPaint));
}

[TestMethod]
public void ShouldHandleMixedPositiveNegativeValues()
{
// Regression test for #2086: Verify that stacked values are calculated correctly
// when there are mixed positive and negative values across multiple series at the same index.
//
// The fix ensures that both End and NegativeEnd are kept in sync to maintain proper
// stacking relationships. This is necessary because:
// - When Series2 starts, it needs to know where Series1 ended, regardless of whether
// Series1's last value was positive or negative
// - Start is derived from the previous series' End in the stacker logic
// - NegativeStart is derived from the previous series' NegativeEnd in the stacker logic
// - For proper stacking, End and NegativeEnd must represent the same cumulative position

// Series 1: positive at index 0, negative at index 1
// Series 2: negative at index 0, positive at index 1
var series1 = new StackedAreaSeries<double>
{
Values = [5, -3],
GeometrySize = 10
};

var series2 = new StackedAreaSeries<double>
{
Values = [-2, 4],
GeometrySize = 10
};

var chart = new SKCartesianChart
{
Width = 1000,
Height = 1000,
Series = [series1, series2],
XAxes = [new Axis()],
YAxes = [new Axis()]
};

_ = chart.GetImage();

var datafactory1 = series1.DataFactory;
var points1 = datafactory1.Fetch(series1, chart.CoreChart).ToArray();

var datafactory2 = series2.DataFactory;
var points2 = datafactory2.Fetch(series2, chart.CoreChart).ToArray();

// For SecondaryValue = 0: series1 = 5 (positive), series2 = -2 (negative)
var point1_0 = points1.Single(p => p.Coordinate.SecondaryValue == 0);
var point2_0 = points2.Single(p => p.Coordinate.SecondaryValue == 0);

// For SecondaryValue = 1: series1 = -3 (negative), series2 = 4 (positive)
var point1_1 = points1.Single(p => p.Coordinate.SecondaryValue == 1);
var point2_1 = points2.Single(p => p.Coordinate.SecondaryValue == 1);

// Verify series1 at index 0 (positive value 5)
// Both End and NegativeEnd are set to 5 to keep them in sync
Assert.AreEqual(0, point1_0.StackedValue.Start, 0.001, "Series1[0] Start should be 0");
Assert.AreEqual(5, point1_0.StackedValue.End, 0.001, "Series1[0] End should be 5");
Assert.AreEqual(0, point1_0.StackedValue.NegativeStart, 0.001, "Series1[0] NegativeStart should be 0");
Assert.AreEqual(5, point1_0.StackedValue.NegativeEnd, 0.001, "Series1[0] NegativeEnd should be 5 (kept in sync with End)");

// Verify series2 at index 0 (negative value -2)
// Start and NegativeStart are both derived from series1's End/NegativeEnd (both 5)
// After adding -2, both End and NegativeEnd become 3
Assert.AreEqual(5, point2_0.StackedValue.Start, 0.001, "Series2[0] Start should be 5 (from Series1 End)");
Assert.AreEqual(3, point2_0.StackedValue.End, 0.001, "Series2[0] End should be 3 (5 + (-2))");
Assert.AreEqual(5, point2_0.StackedValue.NegativeStart, 0.001, "Series2[0] NegativeStart should be 5 (from Series1 NegativeEnd)");
Assert.AreEqual(3, point2_0.StackedValue.NegativeEnd, 0.001, "Series2[0] NegativeEnd should be 3 (kept in sync with End)");

// Verify series1 at index 1 (negative value -3)
// Both End and NegativeEnd are set to -3 to keep them in sync
Assert.AreEqual(0, point1_1.StackedValue.Start, 0.001, "Series1[1] Start should be 0");
Assert.AreEqual(-3, point1_1.StackedValue.End, 0.001, "Series1[1] End should be -3");
Assert.AreEqual(0, point1_1.StackedValue.NegativeStart, 0.001, "Series1[1] NegativeStart should be 0");
Assert.AreEqual(-3, point1_1.StackedValue.NegativeEnd, 0.001, "Series1[1] NegativeEnd should be -3 (kept in sync with End)");

// Verify series2 at index 1 (positive value 4)
// Start and NegativeStart are both derived from series1's End/NegativeEnd (both -3)
// After adding 4, both End and NegativeEnd become 1
Assert.AreEqual(-3, point2_1.StackedValue.Start, 0.001, "Series2[1] Start should be -3 (from Series1 End)");
Assert.AreEqual(1, point2_1.StackedValue.End, 0.001, "Series2[1] End should be 1 (-3 + 4)");
Assert.AreEqual(-3, point2_1.StackedValue.NegativeStart, 0.001, "Series2[1] NegativeStart should be -3 (from Series1 NegativeEnd)");
Assert.AreEqual(1, point2_1.StackedValue.NegativeEnd, 0.001, "Series2[1] NegativeEnd should be 1 (kept in sync with End)");
}
}
84 changes: 84 additions & 0 deletions tests/CoreTests/SeriesTests/StackedStepAreaSeriesTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -348,4 +348,88 @@ public void ShouldPlaceDataLabel()

Assert.IsTrue(!chart.CoreCanvas.ContainsPaintTask(previousPaint));
}

[TestMethod]
public void ShouldHandleMixedPositiveNegativeValues()
{
// Regression test for #2086: Verify that stacked values are calculated correctly
// when there are mixed positive and negative values across multiple series at the same index.
//
// The fix ensures that both End and NegativeEnd are kept in sync to maintain proper
// stacking relationships. This is necessary because:
// - When Series2 starts, it needs to know where Series1 ended, regardless of whether
// Series1's last value was positive or negative
// - Start is derived from the previous series' End in the stacker logic
// - NegativeStart is derived from the previous series' NegativeEnd in the stacker logic
// - For proper stacking, End and NegativeEnd must represent the same cumulative position

// Series 1: positive at index 0, negative at index 1
// Series 2: negative at index 0, positive at index 1
var series1 = new StackedStepAreaSeries<double>
{
Values = [5, -3],
GeometrySize = 10
};

var series2 = new StackedStepAreaSeries<double>
{
Values = [-2, 4],
GeometrySize = 10
};

var chart = new SKCartesianChart
{
Width = 1000,
Height = 1000,
Series = [series1, series2],
XAxes = [new Axis()],
YAxes = [new Axis()]
};

_ = chart.GetImage();

var datafactory1 = series1.DataFactory;
var points1 = datafactory1.Fetch(series1, chart.CoreChart).ToArray();

var datafactory2 = series2.DataFactory;
var points2 = datafactory2.Fetch(series2, chart.CoreChart).ToArray();

// For SecondaryValue = 0: series1 = 5 (positive), series2 = -2 (negative)
var point1_0 = points1.Single(p => p.Coordinate.SecondaryValue == 0);
var point2_0 = points2.Single(p => p.Coordinate.SecondaryValue == 0);

// For SecondaryValue = 1: series1 = -3 (negative), series2 = 4 (positive)
var point1_1 = points1.Single(p => p.Coordinate.SecondaryValue == 1);
var point2_1 = points2.Single(p => p.Coordinate.SecondaryValue == 1);

// Verify series1 at index 0 (positive value 5)
// Both End and NegativeEnd are set to 5 to keep them in sync
Assert.AreEqual(0, point1_0.StackedValue.Start, 0.001, "Series1[0] Start should be 0");
Assert.AreEqual(5, point1_0.StackedValue.End, 0.001, "Series1[0] End should be 5");
Assert.AreEqual(0, point1_0.StackedValue.NegativeStart, 0.001, "Series1[0] NegativeStart should be 0");
Assert.AreEqual(5, point1_0.StackedValue.NegativeEnd, 0.001, "Series1[0] NegativeEnd should be 5 (kept in sync with End)");

// Verify series2 at index 0 (negative value -2)
// Start and NegativeStart are both derived from series1's End/NegativeEnd (both 5)
// After adding -2, both End and NegativeEnd become 3
Assert.AreEqual(5, point2_0.StackedValue.Start, 0.001, "Series2[0] Start should be 5 (from Series1 End)");
Assert.AreEqual(3, point2_0.StackedValue.End, 0.001, "Series2[0] End should be 3 (5 + (-2))");
Assert.AreEqual(5, point2_0.StackedValue.NegativeStart, 0.001, "Series2[0] NegativeStart should be 5 (from Series1 NegativeEnd)");
Assert.AreEqual(3, point2_0.StackedValue.NegativeEnd, 0.001, "Series2[0] NegativeEnd should be 3 (kept in sync with End)");

// Verify series1 at index 1 (negative value -3)
// Both End and NegativeEnd are set to -3 to keep them in sync
Assert.AreEqual(0, point1_1.StackedValue.Start, 0.001, "Series1[1] Start should be 0");
Assert.AreEqual(-3, point1_1.StackedValue.End, 0.001, "Series1[1] End should be -3");
Assert.AreEqual(0, point1_1.StackedValue.NegativeStart, 0.001, "Series1[1] NegativeStart should be 0");
Assert.AreEqual(-3, point1_1.StackedValue.NegativeEnd, 0.001, "Series1[1] NegativeEnd should be -3 (kept in sync with End)");

// Verify series2 at index 1 (positive value 4)
// Start and NegativeStart are both derived from series1's End/NegativeEnd (both -3)
// After adding 4, both End and NegativeEnd become 1
Assert.AreEqual(-3, point2_1.StackedValue.Start, 0.001, "Series2[1] Start should be -3 (from Series1 End)");
Assert.AreEqual(1, point2_1.StackedValue.End, 0.001, "Series2[1] End should be 1 (-3 + 4)");
Assert.AreEqual(-3, point2_1.StackedValue.NegativeStart, 0.001, "Series2[1] NegativeStart should be -3 (from Series1 NegativeEnd)");
Assert.AreEqual(1, point2_1.StackedValue.NegativeEnd, 0.001, "Series2[1] NegativeEnd should be 1 (kept in sync with End)");
}
}
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