Blending using PathGradientBrush Objects in VB.NET

In this article I will explain about Blending Using PathGradientBrush Objects in GDI+.
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The PathGradientBrush object is used to fill a graphics path with a gradient. We can specify the center and boundary colors of a path.
 

The CenterColor and SurroundColors properties are used to specify the center and boundary colors. Listing 9.28 uses the CenterColor and SurroundColors properties; it sets the center color of the path to red and the surrounding color to green.

LISTING 9.28: Blending using PathGradientBrush


Imports
System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Linq
Imports System.Text
Imports System.Windows.Forms
Public Class Form1

    Private Sub Form1_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        Dim g As Graphics = Me.CreateGraphics()
        g.Clear(Me.BackColor)
        ' Create Blend object
        Dim blend As New Blend()
        ' Create point and positions arrays
        Dim factArray As Single() = {0.0F, 0.3F, 0.5F, 1.0F}
        Dim posArray As Single() = {0.0F, 0.2F, 0.6F, 1.0F}
        ' Set Factors and Positions properties of Blend
        blend.Factors = factArray
        blend.Positions = posArray
        ' Set smoothing mode of Graphics object
        g.SmoothingMode = SmoothingMode.AntiAlias
        ' Create path and add a rectangle
        Dim path As New GraphicsPath()
        Dim rect As New Rectangle(10, 20, 200, 200)
        path.AddRectangle(rect)
        ' Create path gradient brush
        Dim rgBrush As New PathGradientBrush(path)
        ' Set Blend and FocusScales properties
        rgBrush.Blend = blend
        rgBrush.FocusScales = New PointF(0.6F, 0.2F)
        Dim colors As Color() = {Color.Green}
        ' Set CenterColor and SurroundColors properties
        rgBrush.CenterColor = Color.Red
        rgBrush.SurroundColors = colors
        g.FillEllipse(rgBrush, rect)
        ' Dispose of object
        g.Dispose()
    End Sub
End Class

If you run the code from Listing 9.28, you will see that the focus is the center of the ellipse and there is scattering in a faded color toward the boundary of the ellipse. The center is red, and the border is green (see Figure 9.37).

The FocusScales property changes the focus point for the gradient falloff. The following code snipped sets the FocusScales property.


rgBrush.FocusScales = New PointF(0.6F, 0.2F)

After FocusScales is set the color of the ellipse changes from the center of the ellipse to a rectangle. Figure 9.38 shows the new output.

FIGURE-9_37.gif

FIGURE 9.37: Blending using PathGradientBrush


We can even specify multiple surrounding colors. For example, we can create an array of different colors and use them for the SurroundedColors property of the brush. To do so, we replace the following line of Listing 9.28.


    
Dim colors As Color() = {Color.Green}

with the following code snipped:


        Dim colors As Color() = {Color.Green, Color.Blue, Color.Red, Color.Yellow}
        rgBrush.SurroundColors = colors

If you add this code to the application, you will see a totally different output. As Figure 9.39 shows, the new ellipse has four different boundary colors.

Like LinearGradientBrush, the PathGradientBrush class provides Blend and InterpolationColors properties. Listing 9.29 shows the InterpolationColors property in use.

FIGURE-9_39.gif

FIGURE 9.39: Blending multiple colors

LISTING 9.29: Using the InterpolationColors property of PathGradientBrush

Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Linq
Imports System.Text
Imports System.Windows.Forms
Public Class Form1

    Private Sub Form1_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        Dim g As Graphics = Me.CreateGraphics()
        g.Clear(Me.BackColor)
        ' Create color and points arrays
        Dim clrArray As Color() = {Color.Red, Color.Blue, Color.Green, Color.Pink, Color.Yellow, Color.DarkTurquoise}
        Dim posArray As Single() = {0.0F, 0.2F, 0.4F, 0.6F, 0.8F, 1.0F}
        ' Create a ColorBlend object and set its Colors and Positions properties
        Dim colorBlend As New ColorBlend()
        colorBlend.Colors = clrArray
        colorBlend.Positions = posArray
        ' Set smoothing mode of Graphics object
        g.SmoothingMode = SmoothingMode.AntiAlias
        ' Create a graphics path and add a rectangle
        Dim path As New GraphicsPath()
        Dim rect As New Rectangle(10, 20, 200, 200)
        path.AddRectangle(rect)
        ' Create a path gradient brush
        Dim rgBrush As New PathGradientBrush(path)
        ' Set Interpolation colors and focus scales
        rgBrush.InterpolationColors = colorBlend
        rgBrush.FocusScales = New PointF(0.6F, 0.2F)
        Dim colors As Color() = {Color.Green}
        ' Set center and surrounding colors
        rgBrush.CenterColor = Color.Red
        rgBrush.SurroundColors = colors
        ' Draw ellipse
        g.FillEllipse(rgBrush, rect)
        ' Dispose of object
        g.Dispose()

    End Sub
End Class

Figure 9.40 shows the output from Listing 9.29.

You can even apply blending on a path gradient brush using the Blend property. Listing 9.30 creates a Blend object and sets the Blend property of the brush.

FIGURE-9_40.gif

FIGURE 9.40: Using the InterpolationColors property of PathGradeintBrush

LISTING 9.30: Using the Blend property of PathGradientBrush

Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Linq
Imports System.Text
Imports System.Windows.Forms
Public Class Form1

    Private Sub Form1_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
        Dim g As Graphics = Me.CreateGraphics()
        g.Clear(Me.BackColor)
        ' Create Blend object
        Dim blend As New Blend()
        ' Create point and position arrays
        Dim factArray As Single() = {0.0F, 0.3F, 0.5F, 1.0F}
        Dim posArray As Single() = {0.0F, 0.2F, 0.6F, 1.0F}
        ' Set Factors and Positions properties of Blend
        blend.Factors = factArray
        blend.Positions = posArray
        ' Set smoothing mode of Graphics object
        g.SmoothingMode = SmoothingMode.AntiAlias
        ' Create path and add a rectangle
        Dim path As New GraphicsPath()
        Dim rect As New Rectangle(10, 20, 200, 200)
        path.AddRectangle(rect)
        ' Create path gradient brush
        Dim rgBrush As New PathGradientBrush(path)
        ' Set Blend and FocusScales properties
        rgBrush.Blend = blend
        rgBrush.FocusScales = New PointF(0.6F, 0.2F)
        Dim colors As Color() = {Color.Green, Color.Blue, Color.Red, Color.Yellow}
        ' Set CenterColor and SurroundColors
        rgBrush.CenterColor = Color.Red
        rgBrush.SurroundColors = colors
        g.FillEllipse(rgBrush, rect)
        ' Dispose of object
        g.Dispose()

    End Sub

End Class

Figure 9.41 shows the output from Listing 9.30. Blending is done with four different colors.

Just as with LinearGradientBrush, you can use the SetBlendTriangularShape methods with PathGradientBrush.

FIGURE-9_41.gif

FIGURE 9.41: Multicolor blending using PathGradientBrush

Conclusion

Hope the article would have helped you in understanding Blending Using PathGradientBrush Objects in GDI+. Read other articles on GDI+ on the website.

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