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Colorize Line and Area Segments

  • 8 minutes to read

A segment colorizer allows you to color-code segments of line and area series.

ChartView supports the point-based segment colorizer that paints line/area segments with colors of point markers, and uses color gradients for segments between different color points.

Line Segments

To colorize line segments:

  1. Assign a colorizer object to the series's SegmentColorizer property (Line1SegmentColorizer/Line2SegmentColorizer for a range area series).

    The following table lists series types and segment colorizers that they support:

    Series Type

    Segment Colorizer

    Line, Area, and RangeArea

    GradientPointBasedSegmentColorizer

    StackedArea

    GradientPointBasedStackedSegmentColorizer

  2. Assign one of the following objects to the segment colorizer's PointColorizer property:

Example

In this example, the spline chart displays the temperature curve colored based on ranges of temperature values.

Line Segment Colorizer

  1. Create a data source - a list of objects that define data points with date-time arguments and numeric values.

    using System;
    using System.Collections.Generic;
    
    namespace SegmentColorizerExample {
    
        public class ViewModel {
            public List<DataItem> Data { get; }
    
            public ViewModel(){
                Data = new List<DataItem>() {
                    new DataItem() { Argument = new DateTime(2018, 1, 1), Value = -17.5 },
                    new DataItem() { Argument = new DateTime(2018, 1, 10), Value = -1.4 },
                    new DataItem() { Argument = new DateTime(2018, 1, 20), Value = -22 },
                    new DataItem() { Argument = new DateTime(2018, 1, 30), Value = -26.2 },
                    new DataItem() { Argument = new DateTime(2018, 2, 10), Value = -17.5 },
                    new DataItem() { Argument = new DateTime(2018, 2, 20), Value = -15.7 },
                    new DataItem() { Argument = new DateTime(2018, 2, 28), Value = -7.8 },
                    new DataItem() { Argument = new DateTime(2018, 3, 10), Value = -8.8 },
                    new DataItem() { Argument = new DateTime(2018, 3, 20), Value = 1.3 },
                    new DataItem() { Argument = new DateTime(2018, 3, 30), Value = -7.5 },
                    new DataItem() { Argument = new DateTime(2018, 4, 10), Value = 1.5 },
                    new DataItem() { Argument = new DateTime(2018, 4, 20), Value = 8.5 },
                    new DataItem() { Argument = new DateTime(2018, 4, 30), Value = 11 },
                    new DataItem() { Argument = new DateTime(2018, 5, 10), Value = 12.2 },
                    new DataItem() { Argument = new DateTime(2018, 5, 20), Value = 13.7 },
                    new DataItem() { Argument = new DateTime(2018, 5, 30), Value = 8.3 },
                    new DataItem() { Argument = new DateTime(2018, 6, 10), Value = 15.3 },
                    new DataItem() { Argument = new DateTime(2018, 6, 20), Value = 19.1 },
                    new DataItem() { Argument = new DateTime(2018, 6, 30), Value = 22.3 },
                    new DataItem() { Argument = new DateTime(2018, 7, 10), Value = 22.2 },
                    new DataItem() { Argument = new DateTime(2018, 7, 20), Value = 24.5 },
                    new DataItem() { Argument = new DateTime(2018, 7, 30), Value = 21.4 },
                    new DataItem() { Argument = new DateTime(2018, 8, 10), Value = 21.2 },
                    new DataItem() { Argument = new DateTime(2018, 8, 20), Value = 15.6 },
                    new DataItem() { Argument = new DateTime(2018, 8, 30), Value = 15 },
                };
            }
        }
    
        public class DataItem {
            public DateTime Argument { get; set; }
            public double Value { get; set; }
        }
    }
    
  2. Assign a GradientPointBasedSegmentColorizer object to the SplineSeries.SegmentColorizer property.
  3. Assign a ValueBandPointColorizer object to the GradientPointBasedSegmentColorizer.PointColorizer property. Populate the colorizer's ColorStops collection with ColorStop objects that specify colors for ranges of temperature values.

    <ContentPage
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        xmlns:dxc="http://schemas.devexpress.com/xamarin/2014/forms/charts"
        x:Class="SegmentColorizerExample.MainPage"
        xmlns:local="clr-namespace:SegmentColorizerExample">
        <ContentPage.BindingContext>
            <local:ViewModel/>
        </ContentPage.BindingContext>
        <dxc:ChartView>
            <dxc:ChartView.Series>
                <dxc:SplineSeries LegendTextPattern="{}{CLV}°C — {CHV}°C">
                    <dxc:SplineSeries.Data>
                        <dxc:SeriesDataAdapter DataSource="{Binding Data}" ArgumentDataMember="Argument">
                               <dxc:ValueDataMember Member="Value" Type="Value" />
                        </dxc:SeriesDataAdapter>
                    </dxc:SplineSeries.Data>
                    <dxc:SplineSeries.SegmentColorizer>
                        <dxc:GradientPointBasedSegmentColorizer>
                            <dxc:GradientPointBasedSegmentColorizer.PointColorizer>
                                <dxc:ValueBandPointColorizer>
                                    <dxc:ValueBandPointColorizer.ColorStops>
                                        <dxc:ColorStop  Color="#00008b" Value1="-40" Value2="-30"/>
                                        <dxc:ColorStop Color="#222b9d" Value1="-30" Value2="-20"/>
                                        <dxc:ColorStop Color="#4556af" Value1="-20" Value2="-15"/>
                                        <dxc:ColorStop Color="#6781c1" Value1="-15" Value2="-10"/>
                                        <dxc:ColorStop Color="#8aacd3" Value1="-10" Value2="-5"/>
                                        <dxc:ColorStop Color="#add8e6" Value1="-5" Value2="0"/>
                                        <dxc:ColorStop Color="#bdbab8" Value1="0" Value2="5"/>
                                        <dxc:ColorStop Color="#cd9d8a" Value1="5" Value2="10"/>
                                        <dxc:ColorStop Color="#de7f5b" Value1="10" Value2="15"/>
                                        <dxc:ColorStop Color="#ee622d" Value1="15" Value2="20"/>
                                        <dxc:ColorStop Color="#ff4500" Value1="20" Value2="30"/>
                                    </dxc:ValueBandPointColorizer.ColorStops>
                                </dxc:ValueBandPointColorizer>
                            </dxc:GradientPointBasedSegmentColorizer.PointColorizer>
                        </dxc:GradientPointBasedSegmentColorizer>
                    </dxc:SplineSeries.SegmentColorizer>
                </dxc:SplineSeries>
            </dxc:ChartView.Series>
            <dxc:ChartView.Legend>
                <dxc:Legend Orientation="TopToBottom"
                            HorizontalPosition="RightOutside"
                            VerticalPosition="Center"/>
            </dxc:ChartView.Legend>
            <dxc:ChartView.AxisX>
                <dxc:DateTimeAxisX>
                    <dxc:DateTimeAxisX.Label>
                         <dxc:AxisLabel TextFormat="MMM"/>
                    </dxc:DateTimeAxisX.Label>
                </dxc:DateTimeAxisX>
            </dxc:ChartView.AxisX>
        </dxc:ChartView>
    </ContentPage>
    

    View Example

Area Segments

To colorize area segments:

  1. Assign a fill colorizer object to the series's FillColorizer property.

    The following table lists area series types and fill colorizers that they support:

    Series Type

    Fill Colorizer

    Area

    SegmentBasedFillColorizer

    RangeArea

    SegmentBasedRangeFillColorizer

    StackedArea

    SegmentBasedStackedFillColorizer

  2. Assign a segment colorizer object to the fill colorizer's SegmentColorizer property.
    The following table lists segment colorizers that fill colorizers support:

    Fill Colorizer

    Segment Colorizer

    SegmentBasedFillColorizer
     

    SegmentBasedRangeFillColorizer
    (SegmentColorizer1/SegmentColorizer2 properties)

    GradientPointBasedSegmentColorizer

    SegmentBasedStackedFillColorizer

    GradientPointBasedStackedSegmentColorizer

  3. Assign one of the following objects to the segment colorizer's PointColorizer property:

Example

In this example, the area chart visualizes the visible light spectrum.

Area Segment Colorizer

  1. Create a data source - a list of objects that define data points with numeric arguments (wavelength) and values (intensity).
  2. Create a colorizer class (LightSpectorColorizer, in this example) that implements the ICustomPointColorizer interface.
    Implement the GetColor method to return a data point's color based on a ColoredPointInfo object passed to the method as a parameter. Use the ColoredPointInfo.NumericArgument property to obtain the data point's argument value.
    This class should also implement the ICustomPointColorizer.GetLegendItemProvider method and the ILegendItemProvider interface to specify legend items that show wavelength colors.

    using System;
    using System.Collections.Generic;
    using System.Globalization;
    using System.IO;
    using DevExpress.XamarinForms.Charts;
    using Xamarin.Forms;
    
    namespace SegmentColorizerExample {
        public class ViewModel {
            LightSpectorData data = new LightSpectorData();
            public IList<NumericData> LightSpectorData => this.data.LightSpectors;
        }
    
        public class LightSpectorData {
            public IList<NumericData> LightSpectors { get; }
    
            public LightSpectorData() {
                LightSpectors = new List<NumericData>();
                using (Stream stream = 
                    GetType().Assembly.GetManifestResourceStream("SegmentColorizerExample.LightSpector.dat")) {
                    StreamReader reader = new StreamReader(stream);
                    string data = reader.ReadToEnd();
                    String[] dataItems = data.Split(new String[] { "\n" }, 
                                         StringSplitOptions.RemoveEmptyEntries);
                    for (int i = 0; i < dataItems.Length; i++) {
                        String[] row = dataItems[i].Split(new String[] { " " }, 
                                       StringSplitOptions.RemoveEmptyEntries);
                        double argument = Convert.ToDouble(row[0], CultureInfo.InvariantCulture);
                        double value = Convert.ToDouble(row[1], CultureInfo.InvariantCulture);
                        LightSpectors.Add(new NumericData(argument, value));
                    }
                }
            }
        }
    
        public class LightSpectorColorizer : ICustomPointColorizer, ILegendItemProvider {
            Color waveLengthToColor(double waveLength) {
                double gamma = 0.8;
                double red = 0.0;
                double green = 0.0;
                double blue = 0.0;
                if (waveLength <= 440) {
                    double attenuation = 0.3 + 0.7 * (waveLength - 380) / (440 - 380);
                    red = Math.Pow((-(waveLength - 440) / (440 - 380)) * attenuation, gamma);
                    green = 0.0;
                    blue = Math.Pow(1.0 * attenuation, gamma);
                }
                else if (waveLength <= 490) {
                    red = 0.0;
                    green = Math.Pow((waveLength - 440) / (490 - 440), gamma);
                    blue = 1.0;
                }
                else if (waveLength <= 510) {
                    red = 0.0;
                    green = 1.0;
                    blue = Math.Pow(-(waveLength - 510) / (510 - 490), gamma);
                }
                else if (waveLength <= 580) {
                    red = Math.Pow((waveLength - 510) / (580 - 510), gamma);
                    green = 1.0;
                    blue = 0.0;
                }
                else if (waveLength <= 645) {
                    red = 1.0;
                    green = Math.Pow(-(waveLength - 645) / (645 - 580), gamma);
                    blue = 0.0;
                }
                else if (waveLength <= 750) {
                    double attenuation = 0.3 + 0.7 * (750 - waveLength) / (750 - 645);
                    red = Math.Pow(1.0 * attenuation, gamma);
                    green = 0.0;
                    blue = 0.0;
                }
                return Color.FromRgb(red, green, blue);
            }
    
            protected virtual double[] GetWavesForLegend() {
                return new double[] { 400, 440, 480, 540, 580, 610, 650 };
            }
    
            Color ICustomPointColorizer.GetColor(ColoredPointInfo info) {
                return waveLengthToColor(info.NumericArgument);
            }
            ILegendItemProvider ICustomPointColorizer.GetLegendItemProvider() {
                return this;
            }
    
            CustomLegendItem ILegendItemProvider.GetLegendItem(int index) {
                double waveLength = GetWavesForLegend()[index];
                Color color = waveLengthToColor(waveLength);
                return new CustomLegendItem($"{waveLength} nm", color);
            }
            int ILegendItemProvider.GetLegendItemCount() {
                return GetWavesForLegend().Length;
            }
        }
    
        public class NumericData {
            public double Argument { get; private set; }
            public double Value { get; private set; }
            public NumericData(double argument, double value) {
                Argument = argument;
                Value = value;
            }
        }
    }
    
  3. Assign a SegmentBasedFillColorizer object to the AreaSeries.FillColorizer property.

  4. Set the SegmentBasedFillColorizer.SegmentColorizer property to a GradientPointBasedSegmentColorizer object, and assign a LightSpectorColorizer object to the GradientPointBasedSegmentColorizer.PointColorizer property.

    <ContentPage
        xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
        xmlns:dxc="http://schemas.devexpress.com/xamarin/2014/forms/charts"
        x:Class="SegmentColorizerExample.MainPage"
        xmlns:local="clr-namespace:SegmentColorizerExample">
        <ContentPage.BindingContext>
            <local:ViewModel/>
        </ContentPage.BindingContext>
        <dxc:ChartView>
            <dxc:ChartView.Series>
                <dxc:AreaSeries>
                    <!-- Bind the series to the data source. -->
                    <dxc:AreaSeries.Data>
                        <dxc:SeriesDataAdapter DataSource="{Binding LightSpectorData}" 
                                               ArgumentDataMember="Argument">
                            <dxc:ValueDataMember Type="Value" Member="Value"/>
                        </dxc:SeriesDataAdapter>
                    </dxc:AreaSeries.Data>
    
                    <dxc:AreaSeries.FillColorizer>
                        <dxc:SegmentBasedFillColorizer>
                            <dxc:SegmentBasedFillColorizer.SegmentColorizer>
                                <dxc:GradientPointBasedSegmentColorizer 
                                    PointColorizer="{local:LightSpectorColorizer}"/>
                            </dxc:SegmentBasedFillColorizer.SegmentColorizer>
                        </dxc:SegmentBasedFillColorizer>
                    </dxc:AreaSeries.FillColorizer>
    
                </dxc:AreaSeries>
            </dxc:ChartView.Series>
    
            <!-- Specify axis and legend settings here. -->
        </dxc:ChartView>
    </ContentPage>
    

    View Example