Plot.PlotFillAboveBelow() #255

ScottPlot · Apr 11, 2020 · 1c1b96a · 1c1b96a
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diff --git a/dev/changelog.md b/dev/changelog.md
@@ -33,6 +33,7 @@ _ScottPlot uses [semantic](https://semver.org/) (major.minor.patch) versioning.
 * The `enableZooming` argument in `WpfPlot.Configure()` and `FormsPlot.Configure()` has been replaced by two arguments `enableRightClickZoom` and `enableScrollWheelZoom` (#338) _Thanks Zach_
 * Improved rendering of legend items for polygons and filled plots (#341) _Thanks @SeidChr_
 * Improved Linux rendering of legend items which use thick lines: axis spans, fills, polygons, etc. (#340) _Thanks @SeidChr_
+* Addded `Plot.PlotFillAboveBelow()` to create a shaded line plot with different colors above/below the baseline. (#255) _Thanks @ckovamees_
 
 ## ScottPlot 4.0.28
 * `Ticks()` now has arguments for numericStringFormat (X and Y) to make it easy to customize formatting of tick labels (percentage, currency, scientific notation, etc.) using standard [numeric format strings](https://docs.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings). Example use is demonstrated in the cookbook. (#336) _Thanks @deiruch_

diff --git a/src/ScottPlot/Plot.cs b/src/ScottPlot/Plot.cs
@@ -486,6 +486,49 @@ public void Clear(Predicate<Plottable> plottablesToClear)
             return PlotPolygon(bothX, bothY, label, lineWidth, lineColor, fill, fillColor, fillAlpha);
         }
 
+        public (PlottablePolygon, PlottablePolygon) PlotFillAboveBelow(
+            double[] xs,
+            double[] ys,
+            string labelAbove = null,
+            string labelBelow = null,
+            double lineWidth = 1,
+            Color? lineColor = null,
+            bool fill = true,
+            Color? fillColorAbove = null,
+            Color? fillColorBelow = null,
+            double fillAlpha = 1,
+            double baseline = 0
+            )
+        {
+            if (xs.Length != ys.Length)
+                throw new ArgumentException("xs and ys must all have the same length");
+
+            double[] xs2 = Tools.Pad(xs, cloneEdges: true);
+            double[] ys2 = Tools.Pad(ys, padWithLeft: baseline, padWithRight: baseline);
+
+            double[] ys2below = new double[ys2.Length];
+            double[] ys2above = new double[ys2.Length];
+            for (int i = 0; i < ys2.Length; i++)
+            {
+                if (ys2[i] < 0)
+                    ys2below[i] = ys2[i];
+                else
+                    ys2above[i] = ys2[i];
+            }
+
+            if (fillColorAbove is null)
+                fillColorAbove = Color.Green;
+            if (fillColorBelow is null)
+                fillColorBelow = Color.Red;
+            if (lineColor is null)
+                lineColor = Color.Black;
+
+            var polyBelow = PlotPolygon(xs2, ys2below, labelAbove, lineWidth, lineColor, fill, fillColorBelow, fillAlpha);
+            var polyAbove = PlotPolygon(xs2, ys2above, labelBelow, lineWidth, lineColor, fill, fillColorAbove, fillAlpha);
+
+            return (polyBelow, polyAbove);
+        }
+
         public PlottableFunction PlotFunction(
             Func<double, double?> function,
             Color? color = null,

diff --git a/tests/PlotTypes/Fill.cs b/tests/PlotTypes/Fill.cs
@@ -84,5 +84,20 @@ public void Test_Fill_SeveralCurvesWithLegend()
 
             TestTools.SaveFig(plt);
         }
+
+        [Test]
+        public void Test_Fill_AboveBelow()
+        {
+            Random rand = new Random(0);
+            var ys = ScottPlot.DataGen.RandomWalk(rand, 1000, offset: -10);
+            var xs = ScottPlot.DataGen.Consecutive(ys.Length, spacing: 0.025);
+
+            var plt = new ScottPlot.Plot(400, 300);
+            plt.PlotFillAboveBelow(xs, ys, fillAlpha: .5, labelAbove: "above", labelBelow: "below");
+            plt.Legend(location: ScottPlot.legendLocation.lowerLeft);
+            plt.AxisAuto(0);
+
+            TestTools.SaveFig(plt);
+        }
     }
 }