GDI+: Gradient Brushes

	GDI+: Gradient Brushes

Gradient Brushes

A gradient brush resembles a solid brush in that it is color-based. Unlike a solid brush, a gradient brush uses two colors. Its main characteristic is that, when used, one color is applied on one side and the other color is applied to the other side. In between, both colors merge to create a transition or fading effect.

There are two types of gradient brushes: linear and path.

Linear Gradient Brushes

A linear gradient is used to apply two colors in a closed shape but from one side of the shape, such as the left, to the other opposite side of the shape, such as the right.

To support linear gradient brushes, the .NET Framework provides the LinearGradientBrush class defined in the System.Drawing.Drawing2D namespace. To specify the starting and the end points inside of the shape that you want to fill, you can use one of the following constructors:

Public Sub LinearGradientBrush(ByVal point1 As Point, ByVal point2 As Point, _
			  ByVal color1 As Color, ByVal color2 As Color)
Public Sub LinearGradientBrush(ByVal point1 As PointF, ByVal point2 As PointF, _
			  ByVal color1 As Color, ByVal color2 As Color)

The first argument, point1, is the pointwhere the drawing would start. The third argument, color1, is the color that would be applied from that point. The second argument, point2, is the pointwhere the drawing would end by applying the color specified by the fourth argument, color2.

Here is an example:

Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) _
			Handles MyBase.Paint        
        Dim lgb As New LinearGradientBrush(New Point(20, 20), New Point(450, 20), _
           Color.DarkGreen, _
           Color.LightBlue)
        e.Graphics.FillRectangle(lgb, 20, 20, 430, 180)
End Sub

By default, the linear gradient brush fills its gradient based on a horizontal line. If you want the color merge to use a different orientation, such as vertical or diagonal, you can use one of the following constructors:

Public Sub LinearGradientBrush(ByVal rect As Rectangle, ByVal color1 As Color, _
			  ByVal color2 As Color , ByVal factor As LinearGradientMode)
Public Sub LinearGradientBrush(ByVal rect As RectangleF, ByVal color1 As Color, _
			  ByVal color2 As Color, ByVal factor As LinearGradientMode)

The first argument, rect, is the rectangle inside of which the colors would be applied. The second argument, color1, is the color that would be applied from a starting point. The second argument, color2, is the color that would be applied at the other end. The factor argument is used to determine the orientation of the merging colors. It has the following members:

Vertical: The first color, color1, is applied to the top section of the rect argument. The second color, color2, is applied to the bottom section of the rect argument:

Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) _
			Handles MyBase.Paint
        Dim rect As New Rectangle(10, 10, 470, 300)
        Dim lgb As New LinearGradientBrush(rect, Color.DarkRed, Color.White, LinearGradientMode.Vertical)
        e.Graphics.FillRectangle(lgb, 10, 10, 450, 280)
End Sub

Horizontal: The first color, color1, is applied to the left section of the rect argument. The second color, color2, is applied to the right section of the rect argument

BackwardDiagonal: The first color, color1, is applied to the top-right corner of the rect argument. The second color, color2, is applied to the bottom-left corner of the rect argument:

ForwardDiagonal: The first color, color1, is applied to the top-left corner of the rect argument. The second color, color2, is applied to the bottom-right corner of the rect argument:

The constructor used to produce the above orientation has the limitation that it provides only four options. If you want, you can apply any angular merge as you see fit. To do this, you can use one of the following constructors:

Public Sub LinearGradientBrush(ByVal rect As Rectangle, ByVal color1 As Color, _
			   ByVal color2 As Color, ByVal angle As Single)
Public Sub LinearGradientBrush(ByVal rect As RectangleF, ByVal color1 As Color, _
			   ByVal color2 As Color, ByVal angle As Single)

The first argument, rect, is the rectangle inside of which the colors would be applied. The last argument, angle, is an angle measured clockwise, that will specify the orientation of the merging colors The second argument, color1, is the color that would be applied from the starting point. The second argument, color2, is the color that would be applied at the other end. Here is an example:

Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) _
			Handles MyBase.Paint
        Dim rect As New Rectangle(10, 10, 470, 300)
        Dim lgb As New LinearGradientBrush(rect, Color.DarkRed, Color.White, -65.24F)
        e.Graphics.FillRectangle(lgb, 10, 10, 450, 280)
End Sub

Path Gradient Brushes

The second type of gradient brush available is referred to as path gradient. This brush is applied on a path created by connecting a series of points to get a closed shape. The interior of the shape can then be filled as a gradient.

To support path brushes, the .NET Framework provides the PathGradientBrush from the System.Drawing.Drawing2D namespace. Two of the constructors of this class are:

Public Sub New(ByVal points() As Point )
Public Sub New(ByVal points() As PointF )

The argument passed to this constructor is an array of type Point. Here is an example:

Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) _
			Handles MyBase.Paint
        Dim ptGraph As Point() = {New Point(10, 10), New Point(450, 10), _
                      New Point(450, 250), New Point(10, 250)}
        Dim pgb As New PathGradientBrush(ptGraph)
        e.Graphics.FillRectangle(pgb, 10, 10, 450, 280)
End Sub


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