WPF RadialGradientBrush

This article demonstrates how to use LinearGradientBrush in WPF using XAML and C#.


Radial Gradient Brush

A radial gradient brush paints an area with a radial gradient that has a circle, along with a focal point, to define the gradient behavior. The focal point defines the center of the gradient and has default value 0.0. The RadialGradientBrush object represents a radial gradient brush. 

Figure 21 shows a radial gradient.

RGB21.jpg

Figure 21. Radial Gradient

 RGB22.jpg

Figure 22. Radial Gradient with Stops

Creating a Radial Gradient Brush

The RadialGradientBrush element in XAML creates a radial gradient brush.

The Center property of the RadialGradientBrush represents the center of the outermost circle of the radial gradient. The default center point of the gradient circle is (0.5, 0.5).

The GradientOrigin property of the RadialGradientBrush represents the location of the focal point of the gradient.  The default focal point of the gradient circle is (0.5, 0.5).

The RadiusX and the RadiusY properties of the RadialGradientBrush represent the X and Y radius of the radial gradient.

The following code snippet creates a radial gradient brush with blue and red colors by setting GradientStops. The GradientOrigin and Center properties are default properties. The code snippet also sets the RadiusX and RadiusY properties.  

<RadialGradientBrush

    GradientOrigin="0.5,0.5"

    Center="0.5,0.5"
    RadiusX="0.5" RadiusY="0.5">

    <RadialGradientBrush.GradientStops>

        <GradientStop Color="Blue" Offset="0" />

        <GradientStop Color="Red" Offset="1.0" />                   

    </RadialGradientBrush.GradientStops>

</RadialGradientBrush>

We can fill a shape with a radial gradient brush by setting a shape's Fill property to the gradient brush. The code snippet in Listing 18 creates a rectangle shape sets the Fill property to a RadialGradientBrush with blue and red colors where center of the radial gradient starts with the blue color.

<Rectangle Width="200" Height="100" Stroke="Black" >

    <Rectangle.Fill>

        <RadialGradientBrush

            GradientOrigin="0.5,0.5"

            Center="0.5,0.5" >

            <RadialGradientBrush.GradientStops>

                <GradientStop Color="Blue" Offset="0" />

                <GradientStop Color="Red" Offset="1.0" />                   

            </RadialGradientBrush.GradientStops>

        </RadialGradientBrush>

    </Rectangle.Fill>

</Rectangle>

Listing 18

The output looks like Figure 23.

RGB23.jpg

Figure 23. A shape filled with a radial gradient brush

Now let's apply multiple stops with multiple colors. The code snippet in Listing 19 creates a radial gradient brush with five stops.

<Rectangle Width="200" Height="100" Stroke="Black" >

    <Rectangle.Fill>

        <RadialGradientBrush

            GradientOrigin="0.5,0.5"

            Center="0.5,0.5" >

            <RadialGradientBrush.GradientStops>

                <GradientStop Color="Blue" Offset="0.1" />

                <GradientStop Color="Orange" Offset="0.25" />

                <GradientStop Color="Yellow" Offset="0.50" />

                <GradientStop Color="Green" Offset="0.75" />

                <GradientStop Color="Red" Offset="1.0" />

            </RadialGradientBrush.GradientStops>

        </RadialGradientBrush>

    </Rectangle.Fill>

</Rectangle>

Listing 19

The new output generated by Listing 96 looks like Figure 34.

RGB24.jpg

Figure 24. A radial gradient brush with 5 stops

The CreateARectangleWithRGBrush method listed in Listing 20 draws same rectangle in Figure 24 dynamically.

public void CreateARectangleWithRGBrush()

{

    // Create a Rectangle

    Rectangle blueRectangle = new Rectangle();

    blueRectangle.Height = 100;

    blueRectangle.Width = 200;

 

    // Create a radial gradient brush with five stops 

    RadialGradientBrush fiveColorRGB = new RadialGradientBrush();

    fiveColorRGB.GradientOrigin = new Point(0.5, 0.5);

    fiveColorRGB.Center = new Point(0.5, 0.5);

 

    // Create and add Gradient stops

    GradientStop blueGS = new GradientStop();

    blueGS.Color = Colors.Blue;

    blueGS.Offset = 0.0;

    fiveColorRGB.GradientStops.Add(blueGS);

 

    GradientStop orangeGS = new GradientStop();

    orangeGS.Color = Colors.Orange;

    orangeGS.Offset = 0.25;

    fiveColorRGB.GradientStops.Add(orangeGS);

 

    GradientStop yellowGS = new GradientStop();

    yellowGS.Color = Colors.Yellow;

    yellowGS.Offset = 0.50;

    fiveColorRGB.GradientStops.Add(yellowGS);

 

    GradientStop greenGS = new GradientStop();

    greenGS.Color = Colors.Green;

    greenGS.Offset = 0.75;

    fiveColorRGB.GradientStops.Add(greenGS);

 

    GradientStop redGS = new GradientStop();

    redGS.Color = Colors.Red;

    redGS.Offset = 1.0;

    fiveColorRGB.GradientStops.Add(redGS);

 

    // Set Fill property of rectangle

    blueRectangle.Fill = fiveColorRGB;

 

    // Add Rectangle to the page

    LayoutRoot.Children.Add(blueRectangle);

}

Listing 20

The following code snippet changes the GradientOrigin and Center properties and now new output looks like Figure 25.

<RadialGradientBrush

            GradientOrigin="0.2,0.5"

            Center="0.1,0.5"

            RadiusX="0.5" RadiusY="0.5">

 

RGB25.jpg

Figure 25. Radial gradient