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Posted 1 Aug 2008


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ColorBlender - Dynamic Gradient Color Blend Creation Control (VB.NET)

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1 Aug 2012CPOL6 min read
How to create a ColorBlend and two color blending UserControls to make it easier.

Image 1


There can be a lot of trial and error, tweaking the code, and running the code many times, to create the correct color blend. I thought it would be nice to have a control like those seen in drawing programs that would create the blend visually to get a proper placement of the colors. I will also try to explain the basics of making a color blended brush to paint with. This is an update to my original ColorBlender. It is still the same core idea, but I was never really satisfied with the layout and how to use it.


Building a two color color blend is fairly simple. Using a LinearGradientBrush from the System.Drawing.Drawing2D namespace, you can paint an area with a blend from one color to another color.

Dim rect As New Rectangle(0, 0, 100, 100)
Using br As New LinearGradientBrush( _
        rect, _
        Color.White, _
        Color.Black, _

    'Fill the rect with the blend
    g.FillRectangle(br, rect)

End Using

If you want more than two colors, a ColorBlend is needed. First, create an array of colors for each position in the blend. Then, create an array of values representing the position of each color in the color array. The first color has a position of 0, and the last color has a position of 1. All the other colors in between have a decimal position value between 0 and 1. After creating the arrays, assign them to the ColorBlend's Colors and Positions properties. Then, create the same LinearGradientBrush as before, setting the two colors to any color just as a placeholder. Set the Brush's InterpolationColors property to the ColorBlend just created to set the new multicolor blend. The LinearGradientBrush can be replaced with the PathGradientBrush for more complex shapes.

Dim blend As ColorBlend = New ColorBlend()

'Add the Array of Color
Dim bColors As Color() = New Color() { _
    Color.Red, _
    Color.Yellow, _
    Color.Lime, _
    Color.Cyan, _
    Color.Blue, _
blend.Colors = bColors

'Add the Array Single (0-1) colorpoints to place each Color
Dim bPts As Single() = New Single() { _
    0, _
    0.327, _
    0.439, _
    0.61, _
    0.777, _
blend.Positions = bPts

Dim rect As New Rectangle(0, 0, 100, 100)
Using br As New LinearGradientBrush( _
        rect, _
        Color.White, _
        Color.Black, _

    'Blend the colors into the Brush
    br.InterpolationColors = blend

    'Fill the rect with the blend
    g.FillRectangle(br, rect)

End Using

gColorBlender Control

The gColorBlender User Control consists of a horizontal bar of color with a starting and ending color gradient. Clicking along the bar adds a new color pointer. The pointer can be dragged back and forth to any position along the bar with the left button, and removed with the right button. Preset color swatches, an owner-drawn ComboBox with all the known colors, a Dimmer Slider, and ARGB Sliders can be changed to alter the color and transparency of the selected pointer. There is a sample preview on the control to display the current blend. The LinearGradientBrush paints the ColorBlend on a line from point A to point B. The PathGradientBrush paints the blend around a path. Right-Click the Sample to change these. The sample can be hidden by setting the ShowSample property to False


  • Public Event BlendChanged()
  • This event will fire in the BuildABlend subroutine.

Control Properties

Here is a list of the primary properties:

  • gColorBlend
  • Array of properties in the cBlenderItems class.

  • cbColor
  • Array of colors used in cBlenderItems class ColorBlend.

  • cbPosition
  • Array of color positions used in ColorBlend.

  • BorderColor
  • For use as an accent color like a border.

  • FocalPoints
  • The CenterPoint and FocusScales for the Drawing.Drawing2D.ColorBlend.

  • BlendGradientType
  • Type of brush used to paint the ColorBlend - Linear or Path.

  • BlendGradientMode
  • Type of linear gradient color blend.

  • BlendPathShape
  • Shape of path for the ColorBlend - Rectangle, Ellipse, Triangle, Polygon.

  • BlendPathCenterPoint
  • Position of the center of the path ColorBlend.

  • BarHeight
  • Height of color blender bar.

  • ShowSample
  • Show or hide the sample.


Methods to use outside the control.

  • GetColorBlendForBrush - Returns a Drawing.Drawing2D.ColorBlend.
  • BlendConvertCenterPoint - Returns a CenterPoint for the given Rectangle relative to the sample CenterPoint.

Mouse Events

Track if the cursor is over a pointer to select or add a pointer, or any of the other rectangles like the sample, border selector, or arrow buttons. Rectangles are easily checked by seeing if the mouse's X, Y is contained within the boundaries of the rectangle, i.e., rectSample.Contains(X, Y). Checking a path has the extra step of being converted to a Region first.

'Convert to Region.
Using PointerRegion As New Region(BuildPointer(GetpX(1)))
    'Is the point inside the region.
    Return PointerRegion.IsVisible(X, Y)
End Using


Contains the routines to draw the pointers, build the brushes, and build the ColorBlend.


Paint the control to a Bitmap to create a buffer, eliminating flicker.

Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
    'Go through each Pointer in the collection
    'to get the current Color and Position arrays

    'Create a canvas to paint on the same size as the control
    Dim bitmapBuffer As Bitmap = New Bitmap(ClientSize.Width, ClientSize.Height)
    Dim g As Graphics = Graphics.FromImage(bitmapBuffer)
    g.SmoothingMode = SmoothingMode.AntiAlias
    g.TextRenderingHint = Drawing.Text.TextRenderingHint.AntiAliasGridFit

    ' Paint the ColorBlender Bar with the Linear Brush
    Dim br As Brush = LinearBrush(rectBar, LinearGradientMode.Horizontal)
    g.FillRectangle(br, rectBar)

    ' Paint the Current Color and Position
    br = New HatchBrush(HatchStyle.LargeCheckerBoard, Color.White, Color.Silver)
    g.FillRectangle(br, rectCurrColor)
    g.FillRectangle(New SolidBrush(Color.FromArgb(gszAlpha.Value, _
                                       gszRed.Value, _
                                       gszGreen.Value, _
                                       gszBlue.Value)), rectCurrColor)
    g.DrawRectangle(Pens.Black, rectCurrColor)
    If CurrPointer > -3 Then
            New Font("Arial", 8, FontStyle.Bold),
            New Rectangle(rectCurrColor.Left - 3, 
                rectCurrColor.Bottom + 1, 50, 30),
            Color.Black, BackColor, TextFormatFlags.Left)

        g.FillRectangles(Brushes.White, New Rectangle() {rectLeft, rectRight})
        g.FillPolygon(Brushes.MediumBlue, ptsLeft)
        g.FillPolygon(Brushes.MediumBlue, ptsRight)
        g.DrawRectangles(Pens.Black, New Rectangle() {rectLeft, rectRight})
    End If

    'Draw all the pointers in their Color at their Position along the Bar
    Using pn As New Pen(Color.Gray, 1) With {.DashStyle = DashStyle.Dash}
        g.DrawLine(pn, rectBar.Left, BarHeight + 7, rectBar.Right, BarHeight + 7)

        pn.Color = Color.Black
        pn.DashStyle = DashStyle.Solid

        DrawPointer(g, StartPointer.ARGB, 0, StartPointer.pIsCurr)
        DrawPointer(g, EndPointer.ARGB, 1, EndPointer.pIsCurr)

        If MiddlePointers IsNot Nothing Then
            For I As Integer = 1 To MiddlePointers.Count
                DrawPointer(g, MiddlePointers(I).ARGB, _
                MiddlePointers(I).pPos, I = CurrPointer)
        End If

    End Using

    If _showSample Then
        'Draw Border
        Dim rectHatch As Rectangle = rectBorderSelect
        rectHatch.Inflate(-1, -1)
        g.FillRectangle(br, rectHatch)
        g.FillRectangle(New SolidBrush(
        If CurrPointer = -3 Then
            Using pn As New Pen(Brushes.Red, 1)
                g.DrawLines(pn, New Point() {
                        New Point(rectBorderSelect.Left - 2, rectBorderSelect.Top + 4),
                        New Point(rectBorderSelect.Left - 2, rectBorderSelect.Top - 2),
                        New Point(rectBorderSelect.Right + 2, rectBorderSelect.Top - 2),
                        New Point(rectBorderSelect.Right + 2, rectBorderSelect.Top + 4)
            End Using
        End If

        ' Paint the ColorBlender Sample with the chosen Shape and BrushType
        Using gp As New GraphicsPath, gph As New GraphicsPath

            rectHatch = rectSample
            rectHatch.Inflate(-1, -1)
            If _gColorBlend.BlendGradientType = eBlendGradientType.Linear Then
                g.FillPath(br, gph)
                br = LinearBrush(rectSample, _gColorBlend.BlendGradientMode)
                gph.AddPath(GetShapePath(rectHatch), False)
                g.FillPath(br, gph)
                gp.AddPath(GetShapePath(rectSample), False)
                br = PathBrush(rectSample)
                TextRenderer.DrawText(g, String.Format(
                     "cp: {1:0.00}, {2:0.00}{0}fs: {3:0.00}, {4:0.00}",
                    New Font("Arial", 8, FontStyle.Regular),
                    New Rectangle(rectSample.Left - 2, 
                        rectSample.Bottom + 2, 
                        rectSample.Width + 2, 30),
                    Color.Black, BackColor, TextFormatFlags.HorizontalCenter)
            End If

            g.FillPath(br, gp)
            Using pn As New Pen(gColorBlend.BorderColor, 2)
                g.DrawPath(pn, gp)
            End Using

        End Using
    End If

    'Draw the entire image to the control in one shot to eliminate flicker
    e.Graphics.DrawImage(bitmapBuffer.Clone, 0, 0)


End Sub


Method that uses the CallByName function to sort the Collection of pointers by the pPos property value.


Is an owner-drawn ComboBox with the DrawItem event overridden to list the known colors.

I finally have a way to add Named Colors to a list ordered by color. The KnownColor enumeration is alphabetic so the only way to do it before was to use a hard coded list of color name strings in the order you wanted rather than the built in enumeration.

Dim cList As New List(Of Color)
For Each s As String In [Enum].GetNames(GetType(KnownColor))
    If Not Color.FromName(s).IsSystemColor Then
    End If
cList.Sort(AddressOf SortColors)
Friend Function SortColors(ByVal x As Color, ByVal y As Color) As Integer
    'To use it first add all non-system colors to a List(Of Color), 
    'sort it by calling colors.Sort(AddressOf SortColors), 
    'then add all the list colors to the combo Items. 
    Dim huecompare As Integer = x.GetHue.CompareTo(y.GetHue)
    Dim satcompare As Integer = x.GetSaturation.CompareTo(y.GetSaturation)
    Dim brightcompare As Integer = x.GetBrightness.CompareTo(y.GetBrightness)
    If huecompare <> 0 Then
        Return huecompare
    ElseIf satcompare <> 0 Then
        Return satcompare
    ElseIf brightcompare <> 0 Then
        Return brightcompare
        Return 0
    End If
End Function

Now add the sorted list to the ComboBox:

With ColorBox
    For Each c As Color In cList
End With

ColorExtensions Module

While working with Color objects named colors sometimes get changed to their ARGB equivalents. So Color.Yellow becomes Color.FromArgb(255, 255, 255, 0). Visually the colors are the same and the actual A, R, G, and B property values are equal, but (Color.Yellow = Color.FromArgb(255, 255, 255, 0)) is False.  Set a color to Color.Yellow and the Name property returns "Yellow".  Set a color using the ARGB values like Color.FromArgb(255, 255, 255, 0) and the Name property returns "ffffff00". This can be a real pain, especially when dealing with the ColorBox that only has named colors in it. To keep the colors consistent I use the GetColorNearestName, GetColorNearestKnownGetColorBestName, and  GetColorBest functions. These functions keep things in order, give the ability to restrict the colors to only KnownColors, or just get the best name possible.

  • GetColorNearestName: Returns the Name of the KnownColor that most closely matches the given color
  • GetColorNearestKnown: Returns the KnownColor that most closely matches the given color
  • GetColorBestName: If the given color matches a KnownColor that name is returned, otherwise the current name is returned
  • GetColorBest: If the given color matches a KnownColor the KnownColor is returned, otherwise the ARGB Color is returned

Additional functions in this Module are:

  • DimTheColor: Takes the given color and lightens or darkens it by the given value
  • GrayTheColor: Takes the given color and returns its gray equivalent

I made these functions into Extensions. by adding the <Extension()> attribute from the System.Runtime.CompilerServices namespace. Now any object with data type Color will have these functions directly associated to them. In other words typing a period after the color object will show these functions in the IntelliSense.

Image 2


The control can be used as a stand alone control directly on the form like in the main source project.

As shown in the demo project, it can also be used in a ToolStripDropDown:

Image 3

or as a TypeEditor in the PropertyGrid.

Image 4


Use of the Type Converters and editors are fully explained my UITypeEditor article: UITypeEditorsDemo[^].


The cPointer class contains four properties.

  • pPos - Position of the color.
  • pColor - Color at the position value.
  • pAlpha - Value from 0 to 255 that is the Transparency level of the color.
  • pIsCurr - The pointer currently selected.


  • Version 1.0 - July 2008.
  • Version 2.0.3 July 2012.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Software Developer
United States United States
I first got hooked on programing with the TI994A. After it finally lost all support I reluctantly moved to the Apple IIe. Thank You BeagleBros for getting me through. I wrote programs for my Scuba buisness during this time. Currently I am a Database manager and software developer. I started with VBA and VB6 and now having fun with VB.NET/WPF/C#...

Comments and Discussions

QuestionMy vote of 5 and have a question Pin
EzequielKees20-Jan-16 14:01
MemberEzequielKees20-Jan-16 14:01 
AnswerRe: My vote of 5 and have a question Pin
SSDiver211220-Jan-16 17:37
MemberSSDiver211220-Jan-16 17:37 
GeneralRe: My vote of 5 and have a question Pin
EzequielKees21-Jan-16 7:58
MemberEzequielKees21-Jan-16 7:58 
GeneralMy vote of 5 Pin
Scryaga22-Sep-12 3:44
MemberScryaga22-Sep-12 3:44 
BugContextMenu checked item not kept in sync with direct Property Grid changes Pin
DlkEng16-Aug-12 9:50
MemberDlkEng16-Aug-12 9:50 
GeneralRe: ContextMenu checked item not kept in sync with direct Property Grid changes Pin
SSDiver211216-Aug-12 19:04
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GeneralNice! Pin
Brisingr Aerowing1-Aug-12 4:40
professionalBrisingr Aerowing1-Aug-12 4:40 
GeneralMy vote of 5 Pin
Manoj Kumar Choubey17-Feb-12 0:23
professionalManoj Kumar Choubey17-Feb-12 0:23 
QuestionThx Pin
bboyse8-Feb-12 18:46
Memberbboyse8-Feb-12 18:46 
GeneralMy vote of 5 Pin
karenpayne12-Jun-11 7:32
Memberkarenpayne12-Jun-11 7:32 
GeneralYour articles are alway very cool! Pin
Shane Story3-Feb-09 4:03
MemberShane Story3-Feb-09 4:03 
GeneralVery Nice Pin
Paul Conrad2-Aug-08 20:34
professionalPaul Conrad2-Aug-08 20:34 

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