docs-desktop/dotnet-desktop-guide/framework/winforms/advanced/how-to-create-a-path-gradient.md

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How to: Create a Path Gradient	03/30/2017	csharp vb	path gradients [Windows Forms], creating gradients [Windows Forms], creating path graphics paths [Windows Forms], creating gradient	1948e834-e104-481c-b71d-d8aa9e4d106e

How to: Create a Path Gradient

The xref:System.Drawing.Drawing2D.PathGradientBrush class allows you to customize the way you fill a shape with gradually changing colors. For example, you can specify one color for the center of a path and another color for the boundary of a path. You can also specify separate colors for each of several points along the boundary of a path.

Note

In GDI+, a path is a sequence of lines and curves maintained by a xref:System.Drawing.Drawing2D.GraphicsPath object. For more information about GDI+ paths, see Graphics Paths in GDI+ and Constructing and Drawing Paths.

The examples in this article are methods that are called from a control's xref:System.Windows.Forms.Control.Paint event handler.

To fill an ellipse with a path gradient

• The following example fills an ellipse with a path gradient brush. The center color is set to blue and the boundary color is set to aqua. The following illustration shows the filled ellipse.

  

  By default, a path gradient brush does not extend outside the boundary of the path. If you use the path gradient brush to fill a figure that extends beyond the boundary of the path, the area of the screen outside the path will not be filled.

  The following illustration shows what happens if you change the xref:System.Drawing.Graphics.FillEllipse%2A?displayProperty=nameWithType call in the following code to e.Graphics.FillRectangle(pthGrBrush, 0, 10, 200, 40):

  

  [!code-csharpSystem.Drawing.UsingaGradientBrush#11] [!code-vbSystem.Drawing.UsingaGradientBrush#11]

  The preceding code example is designed for use with Windows Forms, and it requires the xref:System.Windows.Forms.PaintEventArgs e, which is a parameter of xref:System.Windows.Forms.PaintEventHandler.

To specify points on the boundary

• The following example constructs a path gradient brush from a star-shaped path. The code sets the xref:System.Drawing.Drawing2D.PathGradientBrush.CenterColor%2A property, which sets the color at the centroid of the star to red. Then the code sets the xref:System.Drawing.Drawing2D.PathGradientBrush.SurroundColors%2A property to specify various colors (stored in the colors array) at the individual points in the points array. The final code statement fills the star-shaped path with the path gradient brush.

  [!code-csharpSystem.Drawing.UsingaGradientBrush#12] [!code-vbSystem.Drawing.UsingaGradientBrush#12]

• The following example draws a path gradient without a xref:System.Drawing.Drawing2D.GraphicsPath object in the code. The particular xref:System.Drawing.Drawing2D.PathGradientBrush.%23ctor%2A constructor in the example receives an array of points but does not require a xref:System.Drawing.Drawing2D.GraphicsPath object. Also, note that the xref:System.Drawing.Drawing2D.PathGradientBrush is used to fill a rectangle, not a path. The rectangle is larger than the closed path used to define the brush, so some of the rectangle is not painted by the brush. The following illustration shows the rectangle (dotted line) and the portion of the rectangle painted by the path gradient brush:

  

  [!code-csharpSystem.Drawing.UsingaGradientBrush#13] [!code-vbSystem.Drawing.UsingaGradientBrush#13]

To customize a path gradient

• One way to customize a path gradient brush is to set its xref:System.Drawing.Drawing2D.PathGradientBrush.FocusScales%2A property. The focus scales specify an inner path that lies inside the main path. The center color is displayed everywhere inside that inner path rather than only at the center point.

  The following example creates a path gradient brush based on an elliptical path. The code sets the boundary color to blue, sets the center color to aqua, and then uses the path gradient brush to fill the elliptical path.

  Next, the code sets the focus scales of the path gradient brush. The x focus scale is set to 0.3, and the y focus scale is set to 0.8. The code calls the xref:System.Drawing.Graphics.TranslateTransform%2A method of a xref:System.Drawing.Graphics object so that the subsequent call to xref:System.Drawing.Graphics.FillPath%2A fills an ellipse that sits to the right of the first ellipse.

  To see the effect of the focus scales, imagine a small ellipse that shares its center with the main ellipse. The small (inner) ellipse is the main ellipse scaled (about its center) horizontally by a factor of 0.3 and vertically by a factor of 0.8. As you move from the boundary of the outer ellipse to the boundary of the inner ellipse, the color changes gradually from blue to aqua. As you move from the boundary of the inner ellipse to the shared center, the color remains aqua.

  The following illustration shows the output of the following code. The ellipse on the left is aqua only at the center point. The ellipse on the right is aqua everywhere inside the inner path.

[!code-csharpSystem.Drawing.UsingaGradientBrush#14] [!code-vbSystem.Drawing.UsingaGradientBrush#14]

To customize with interpolation

• Another way to customize a path gradient brush is to specify an array of interpolation colors and an array of interpolation positions.

  The following example creates a path gradient brush based on a triangle. The code sets the xref:System.Drawing.Drawing2D.PathGradientBrush.InterpolationColors%2A property of the path gradient brush to specify an array of interpolation colors (dark green, aqua, blue) and an array of interpolation positions (0, 0.25, 1). As you move from the boundary of the triangle to the center point, the color changes gradually from dark green to aqua and then from aqua to blue. The change from dark green to aqua happens in 25 percent of the distance from dark green to blue.

  The following illustration shows the triangle filled with the custom path gradient brush.

  

  [!code-csharpSystem.Drawing.UsingaGradientBrush#15] [!code-vbSystem.Drawing.UsingaGradientBrush#15]

To set the center point

• By default, the center point of a path gradient brush is at the centroid of the path used to construct the brush. You can change the location of the center point by setting the xref:System.Drawing.Drawing2D.PathGradientBrush.CenterPoint%2A property of the xref:System.Drawing.Drawing2D.PathGradientBrush class.

  The following example creates a path gradient brush based on an ellipse. The center of the ellipse is at (70, 35), but the center point of the path gradient brush is set to (120, 40).

  [!code-csharpSystem.Drawing.UsingaGradientBrush#16] [!code-vbSystem.Drawing.UsingaGradientBrush#16]

  The following illustration shows the filled ellipse and the center point of the path gradient brush:

  

• You can set the center point of a path gradient brush to a location outside the path that was used to construct the brush. The following example replaces the call to set the xref:System.Drawing.Drawing2D.PathGradientBrush.CenterPoint%2A property in the preceding code.

  [!code-csharpSystem.Drawing.UsingaGradientBrush#17] [!code-vbSystem.Drawing.UsingaGradientBrush#17]

  The following illustration shows the output with this change:

  

  In the preceding illustration, the points at the far right of the ellipse are not pure blue (although they are very close). The colors in the gradient are positioned as if the fill reached the point (145, 35) where the color would be pure blue (0, 0, 255). But the fill never reaches (145, 35) because a path gradient brush paints only inside its path.

Compiling the Code

The preceding examples are designed for use with Windows Forms, and they require xref:System.Windows.Forms.PaintEventArgs e, which is a parameter of the xref:System.Windows.Forms.Control.Paint event handler.

See also

• Using a Gradient Brush to Fill Shapes