显示渐变填充(摘自：msdn)

NotInheritable Public Class GradientFill
' This method wraps the PInvoke to GradientFill.
' Parmeters:
'  gr - The Graphics object we are filling
'  rc - The rectangle to fill
'  startColor - The starting color for the fill
'  endColor - The ending color for the fill
'  fillDir - The direction to fill
'
' Returns true if the call to GradientFill succeeded; false
' otherwise.
Public Shared Function Fill(ByVal gr As Graphics, ByVal rc As Rectangle, ByVal startColor As Color, _
ByVal endColor As Color, ByVal fillDir As FillDirection) As Boolean 
' Initialize the data to be used in the call to GradientFill.
Dim tva(1) As Win32Helper.TRIVERTEX
tva(0) = New Win32Helper.TRIVERTEX(rc.X, rc.Y, startColor)
tva(1) = New Win32Helper.TRIVERTEX(rc.Right, rc.Bottom, endColor)
Dim gra() As Win32Helper.GRADIENT_RECT = {New Win32Helper.GRADIENT_RECT(0, 1)}
' Get the hDC from the Graphics object.
Dim hdc As IntPtr = gr.GetHdc()
' PInvoke to GradientFill.
Dim b As Boolean
b = Win32Helper.GradientFill(hdc, tva, CType(tva.Length, System.Int32), gra, CType(gra.Length, System.Int32), CType(fillDir, System.Int32))
System.Diagnostics.Debug.Assert(b, String.Format("GradientFill failed: {0}", System.Runtime.InteropServices.Marshal.GetLastWin32Error()))
' Release the hDC from the Graphics object.
gr.ReleaseHdc(hdc)
Return b
End Function
' The direction to the GradientFill will follow
Public Enum FillDirection
' The fill goes horizontally
LeftToRight = Win32Helper.GRADIENT_FILL_RECT_H
' The fill goes vertically
TopToBottom = Win32Helper.GRADIENT_FILL_RECT_V
End Enum
End Class
' Extends the standard button control and performs
' custom drawing with a GradientFill background.
Public Class GradientFilledButton
Inherits Control
Private components As System.ComponentModel.IContainer = Nothing
Public Sub New()
components = New System.ComponentModel.Container()
Me.Font = New Font(Me.Font.Name, Me.Font.Size, FontStyle.Bold)
End Sub
' Controls the direction in which the button is filled.
Public Property FillDirection() As GradientFill.FillDirection
Get
Return fillDirectionValue
End Get
Set(ByVal value As GradientFill.FillDirection)
fillDirectionValue = value
Invalidate()
End Set
End Property
Private fillDirectionValue As GradientFill.FillDirection
' The start color for the GradientFill. This is the color
' at the left or top of the control depeneding on the value
' of the FillDirection property.
Public Property StartColor() As Color
Get
Return startColorValue
End Get
Set(ByVal value As Color)
startColorValue = value
Invalidate()
End Set
End Property
Private startColorValue As Color = Color.Red
' The end color for the GradientFill. This is the color
' at the right or bottom of the control depending on the value
' of the FillDirection property
Public Property EndColor() As Color
Get
Return endColorValue
End Get
Set(ByVal value As Color)
endColorValue = value
Invalidate()
End Set
End Property
Private endColorValue As Color = Color.Blue
' This is the offset from the left or top edge
'  of the button to start the gradient fill.
Public Property StartOffset() As Integer
Get
Return startOffsetValue
End Get
Set(ByVal value As Integer)
startOffsetValue = value
Invalidate()
End Set
End Property
Private startOffsetValue As Integer
' This is the offset from the right or bottom edge
'  of the button to end the gradient fill.
Public Property EndOffset() As Integer
Get
Return endOffsetValue
End Get
Set(ByVal value As Integer)
endOffsetValue = value
Invalidate()
End Set
End Property
Private endOffsetValue As Integer
' Used to double-buffer our drawing to avoid flicker
' between painting the background, border, focus-rect
' and the text of the control.
Private Property DoubleBufferImage() As Bitmap
Get
If bmDoubleBuffer Is Nothing Then
bmDoubleBuffer = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height)
End If
Return bmDoubleBuffer
End Get
Set(ByVal value As Bitmap)
If Not (bmDoubleBuffer Is Nothing) Then
bmDoubleBuffer.Dispose()
End If
bmDoubleBuffer = value
End Set
End Property
Private bmDoubleBuffer As Bitmap
' Called when the control is resized. When that happens,
' recreate the bitmap used for double-buffering.
Protected Overrides Sub OnResize(ByVal e As EventArgs)
DoubleBufferImage = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height)
MyBase.OnResize(e)
End Sub
' Called when the control gets focus. Need to repaint
' the control to ensure the focus rectangle is drawn correctly.
Protected Overrides Sub OnGotFocus(ByVal e As EventArgs)
MyBase.OnGotFocus(e)
Me.Invalidate()
End Sub
' Called when the control loses focus. Need to repaint
' the control to ensure the focus rectangle is removed.
Protected Overrides Sub OnLostFocus(ByVal e As EventArgs)
MyBase.OnLostFocus(e)
Me.Invalidate()
End Sub
Protected Overrides Sub OnMouseMove(ByVal e As MouseEventArgs)
If Me.Capture Then
Dim coord As New Point(e.X, e.Y)
If Me.ClientRectangle.Contains(coord) <> Me.ClientRectangle.Contains(lastCursorCoordinates) Then
DrawButton(Me.ClientRectangle.Contains(coord))
End If
lastCursorCoordinates = coord
End If
MyBase.OnMouseMove(e)
End Sub
' The coordinates of the cursor the last time
' there was a MouseUp or MouseDown message.
Private lastCursorCoordinates As Point
Protected Overrides Sub OnMouseDown(ByVal e As MouseEventArgs)
If e.Button = System.Windows.Forms.MouseButtons.Left Then
' Start capturing the mouse input
Me.Capture = True
' Get the focus because button is clicked.
Me.Focus()
' draw the button
DrawButton(True)
End If
MyBase.OnMouseDown(e)
End Sub
Protected Overrides Sub OnMouseUp(ByVal e As MouseEventArgs)
Me.Capture = False
DrawButton(False)
MyBase.OnMouseUp(e)
End Sub
Private bGotKeyDown As Boolean = False
Protected Overrides Sub OnKeyDown(ByVal e As KeyEventArgs)
bGotKeyDown = True
Select Case e.KeyCode
Case Keys.Space, Keys.Enter
DrawButton(True)
Case Keys.Up, Keys.Left
Me.Parent.SelectNextControl(Me, False, False, True, True)
Case Keys.Down, Keys.Right
Me.Parent.SelectNextControl(Me, True, False, True, True)
Case Else
bGotKeyDown = False
MyBase.OnKeyDown(e)
End Select
End Sub
Protected Overrides Sub OnKeyUp(ByVal e As KeyEventArgs)
Select Case e.KeyCode
Case Keys.Space, Keys.Enter
If bGotKeyDown Then
DrawButton(False)
OnClick(EventArgs.Empty)
bGotKeyDown = False
End If
Case Else
MyBase.OnKeyUp(e)
End Select
End Sub
' Override this method with no code to avoid flicker.
Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs)
End Sub
Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
DrawButton(e.Graphics, Me.Capture AndAlso Me.ClientRectangle.Contains(lastCursorCoordinates))
End Sub
' Gets a Graphics object for the provided window handle
'  and then calls DrawButton(Graphics, bool).
' If pressed is true, the button is drawn
' in the depressed state.
Overloads Sub DrawButton(ByVal pressed As Boolean)
Dim gr As Graphics = Me.CreateGraphics()
DrawButton(gr, pressed)
gr.Dispose()
End Sub
' Draws the button on the specified Grapics
' in the specified state.
'
' Parameters:
'  gr - The Graphics object on which to draw the button.
'  pressed - If true, the button is drawn in the depressed state.
Overloads Sub DrawButton(ByVal gr As Graphics, ByVal pressed As Boolean)
' Get a Graphics object from the background image.
Dim gr2 As Graphics = Graphics.FromImage(DoubleBufferImage)
' Fill solid up until where the gradient fill starts.
If startOffsetValue > 0 Then
If fillDirectionValue = GradientFill.FillDirection.LeftToRight Then
If pressed Then
gr2.FillRectangle(New SolidBrush(EndColor), 0, 0, startOffsetValue, Height)
Else
gr2.FillRectangle(New SolidBrush(StartColor), 0, 0, startOffsetValue, Height)
End If
Else
If pressed Then
gr2.FillRectangle(New SolidBrush(EndColor), 0, 0, Width, startOffsetValue)
Else
gr2.FillRectangle(New SolidBrush(StartColor), 0, 0, Width, startOffsetValue)
End If
End If
End If
' Draw the gradient fill.
Dim rc As Rectangle = Me.ClientRectangle
If fillDirectionValue = GradientFill.FillDirection.LeftToRight Then
rc.X = startOffsetValue
rc.Width = rc.Width - startOffsetValue - endOffsetValue
Else
rc.Y = startOffsetValue
rc.Height = rc.Height - startOffsetValue - endOffsetValue
End If
If pressed Then
GradientFill.Fill(gr2, rc, endColorValue, startColorValue, fillDirectionValue)
Else
GradientFill.Fill(gr2, rc, startColorValue, endColorValue, fillDirectionValue)
End If
' Fill solid from the end of the gradient fill
' to the edge of the button.
If endOffsetValue > 0 Then
If fillDirectionValue = GradientFill.FillDirection.LeftToRight Then
If pressed Then
gr2.FillRectangle(New SolidBrush(StartColor), rc.X + rc.Width, 0, endOffsetValue, Height)
Else
gr2.FillRectangle(New SolidBrush(EndColor), rc.X + rc.Width, 0, endOffsetValue, Height)
End If
Else
If pressed Then
gr2.FillRectangle(New SolidBrush(StartColor), 0, rc.Y + rc.Height, Width, endOffsetValue)
Else
gr2.FillRectangle(New SolidBrush(StartColor), 0, rc.Y + rc.Height, Width, endOffsetValue)
End If
End If
End If
' Draw the text.
Dim sf As New StringFormat()
sf.Alignment = StringAlignment.Center
sf.LineAlignment = StringAlignment.Center
gr2.DrawString(Me.Text, Me.Font, New SolidBrush(Me.ForeColor), Me.ClientRectangle, sf)
' Draw the border.
' Need to shrink the width and height by 1 otherwise
' there will be no border on the right or bottom.
rc = Me.ClientRectangle
rc.Width -= 1
rc.Height -= 1
Dim pen As New Pen(SystemColors.WindowFrame)
gr2.DrawRectangle(pen, rc)
' Draw from the background image onto the screen.
gr.DrawImage(DoubleBufferImage, 0, 0)
gr2.Dispose()
End Sub
Protected Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing AndAlso Not (components Is Nothing) Then
components.Dispose()
End If
MyBase.Dispose(disposing)
End Sub
End Class

public sealed class GradientFill
{
// This method wraps the PInvoke to GradientFill.
// Parmeters:
//  gr - The Graphics object we are filling
//  rc - The rectangle to fill
//  startColor - The starting color for the fill
//  endColor - The ending color for the fill
//  fillDir - The direction to fill
//
// Returns true if the call to GradientFill succeeded; false
// otherwise.
public static bool Fill(
Graphics gr,
Rectangle rc,
Color startColor, Color endColor,
FillDirection fillDir)
{
// Initialize the data to be used in the call to GradientFill.
Win32Helper.TRIVERTEX[] tva = new Win32Helper.TRIVERTEX[2];
tva[0] = new Win32Helper.TRIVERTEX(rc.X, rc.Y, startColor);
tva[1] = new Win32Helper.TRIVERTEX(rc.Right, rc.Bottom, endColor);
Win32Helper.GRADIENT_RECT[] gra = new Win32Helper.GRADIENT_RECT[] {
new Win32Helper.GRADIENT_RECT(0, 1)};
// Get the hDC from the Graphics object.
IntPtr hdc = gr.GetHdc();
// PInvoke to GradientFill.
bool b;
b = Win32Helper.GradientFill(
hdc,
tva,
(uint)tva.Length,
gra,
(uint)gra.Length,
(uint)fillDir);
System.Diagnostics.Debug.Assert(b, string.Format(
"GradientFill failed: {0}",
System.Runtime.InteropServices.Marshal.GetLastWin32Error()));
// Release the hDC from the Graphics object.
gr.ReleaseHdc(hdc);
return b;
}
// The direction to the GradientFill will follow
public enum FillDirection
{
//
// The fill goes horizontally
//
LeftToRight = Win32Helper.GRADIENT_FILL_RECT_H,
//
// The fill goes vertically
//
TopToBottom = Win32Helper.GRADIENT_FILL_RECT_V
}
}
// Extends the standard button control and performs
// custom drawing with a GradientFill background.
public class GradientFilledButton : Control
{
private System.ComponentModel.IContainer components = null;
public GradientFilledButton()
{
components = new System.ComponentModel.Container();
this.Font = new Font(this.Font.Name, this.Font.Size, FontStyle.Bold);
}
// Controls the direction in which the button is filled.
public GradientFill.FillDirection FillDirection
{
get
{
return fillDirectionValue;
}
set
{
fillDirectionValue = value;
Invalidate();
}
}
private GradientFill.FillDirection fillDirectionValue;
// The start color for the GradientFill. This is the color
// at the left or top of the control depeneding on the value
// of the FillDirection property.
public Color StartColor
{
get { return startColorValue; }
set
{
startColorValue = value;
Invalidate();
}
}
private Color startColorValue = Color.Red;
// The end color for the GradientFill. This is the color
// at the right or bottom of the control depending on the value
// of the FillDirection property
public Color EndColor
{
get { return endColorValue; }
set
{
endColorValue = value;
Invalidate();
}
}
private Color endColorValue = Color.Blue;
// This is the offset from the left or top edge
//  of the button to start the gradient fill.
public int StartOffset
{
get { return startOffsetValue; }
set
{
startOffsetValue = value;
Invalidate();
}
}
private int startOffsetValue;
// This is the offset from the right or bottom edge
//  of the button to end the gradient fill.
public int EndOffset
{
get { return endOffsetValue; }
set
{
endOffsetValue = value;
Invalidate();
}
}
private int endOffsetValue;
// Used to double-buffer our drawing to avoid flicker
// between painting the background, border, focus-rect
// and the text of the control.
private Bitmap DoubleBufferImage
{
get
{
if (bmDoubleBuffer == null)
bmDoubleBuffer = new Bitmap(
this.ClientSize.Width,
this.ClientSize.Height);
return bmDoubleBuffer;
}
set
{
if (bmDoubleBuffer != null)
bmDoubleBuffer.Dispose();
bmDoubleBuffer = value;
}
}
private Bitmap bmDoubleBuffer;
// Called when the control is resized. When that happens,
// recreate the bitmap used for double-buffering.
protected override void OnResize(EventArgs e)
{
DoubleBufferImage = new Bitmap(
this.ClientSize.Width,
this.ClientSize.Height);
base.OnResize(e);
}
// Called when the control gets focus. Need to repaint
// the control to ensure the focus rectangle is drawn correctly.
protected override void OnGotFocus(EventArgs e)
{
base.OnGotFocus(e);
this.Invalidate();
}
//
// Called when the control loses focus. Need to repaint
// the control to ensure the focus rectangle is removed.
protected override void OnLostFocus(EventArgs e)
{
base.OnLostFocus(e);
this.Invalidate();
}
protected override void OnMouseMove(MouseEventArgs e)
{
if (this.Capture)
{
Point coord = new Point(e.X, e.Y);
if (this.ClientRectangle.Contains(coord) !=
this.ClientRectangle.Contains(lastCursorCoordinates))
{
DrawButton(this.ClientRectangle.Contains(coord));
}
lastCursorCoordinates = coord;
}
base.OnMouseMove(e);
}
// The coordinates of the cursor the last time
// there was a MouseUp or MouseDown message.
Point lastCursorCoordinates;
protected override void OnMouseDown(MouseEventArgs e)
{
if (e.Button == MouseButtons.Left)
{
// Start capturing the mouse input
this.Capture = true;
// Get the focus because button is clicked.
this.Focus();
// draw the button
DrawButton(true);
}
base.OnMouseDown(e);
}
protected override void OnMouseUp(MouseEventArgs e)
{
this.Capture = false;
DrawButton(false);
base.OnMouseUp(e);
}
bool bGotKeyDown = false;
protected override void OnKeyDown(KeyEventArgs e)
{
bGotKeyDown = true;
switch (e.KeyCode)
{
case Keys.Space:
case Keys.Enter:
DrawButton(true);
break;
case Keys.Up:
case Keys.Left:
this.Parent.SelectNextControl(this, false, false, true, true);
break;
case Keys.Down:
case Keys.Right:
this.Parent.SelectNextControl(this, true, false, true, true);
break;
default:
bGotKeyDown = false;
base.OnKeyDown(e);
break;
}
}
protected override void OnKeyUp(KeyEventArgs e)
{
switch (e.KeyCode)
{
case Keys.Space:
case Keys.Enter:
if (bGotKeyDown)
{
DrawButton(false);
OnClick(EventArgs.Empty);
bGotKeyDown = false;
}
break;
default:
base.OnKeyUp(e);
break;
}
}
// Override this method with no code to avoid flicker.
protected override void OnPaintBackground(PaintEventArgs e)
{
}
protected override void OnPaint(PaintEventArgs e)
{
DrawButton(e.Graphics, this.Capture &&
(this.ClientRectangle.Contains(lastCursorCoordinates)));
}
//
// Gets a Graphics object for the provided window handle
//  and then calls DrawButton(Graphics, bool).
//
// If pressed is true, the button is drawn
// in the depressed state.
void DrawButton(bool pressed)
{
Graphics gr = this.CreateGraphics();
DrawButton(gr, pressed);
gr.Dispose();
}
// Draws the button on the specified Grapics
// in the specified state.
//
// Parameters:
//  gr - The Graphics object on which to draw the button.
//  pressed - If true, the button is drawn in the depressed state.
void DrawButton(Graphics gr, bool pressed)
{
// Get a Graphics object from the background image.
Graphics gr2 = Graphics.FromImage(DoubleBufferImage);
// Fill solid up until where the gradient fill starts.
if (startOffsetValue > 0)
{
if (fillDirectionValue ==
GradientFill.FillDirection.LeftToRight)
{
gr2.FillRectangle(
new SolidBrush(pressed ? EndColor : StartColor),
0, 0, startOffsetValue, Height);
}
else
{
gr2.FillRectangle(
new SolidBrush(pressed ? EndColor : StartColor),
0, 0, Width, startOffsetValue);
}
}
// Draw the gradient fill.
Rectangle rc = this.ClientRectangle;
if (fillDirectionValue == GradientFill.FillDirection.LeftToRight)
{
rc.X = startOffsetValue;
rc.Width = rc.Width - startOffsetValue - endOffsetValue;
}
else
{
rc.Y = startOffsetValue;
rc.Height = rc.Height - startOffsetValue - endOffsetValue;
}
GradientFill.Fill(
gr2,
rc,
pressed ? endColorValue : startColorValue,
pressed ? startColorValue : endColorValue,
fillDirectionValue);
// Fill solid from the end of the gradient fill
// to the edge of the button.
if (endOffsetValue > 0)
{
if (fillDirectionValue ==
GradientFill.FillDirection.LeftToRight)
{
gr2.FillRectangle(
new SolidBrush(pressed ? StartColor : EndColor),
rc.X + rc.Width, 0, endOffsetValue, Height);
}
else
{
gr2.FillRectangle(
new SolidBrush(pressed ? StartColor : EndColor),
0, rc.Y + rc.Height, Width, endOffsetValue);
}
}
// Draw the text.
StringFormat sf = new StringFormat();
sf.Alignment = StringAlignment.Center;
sf.LineAlignment = StringAlignment.Center;
gr2.DrawString(this.Text, this.Font,
new SolidBrush(this.ForeColor),
this.ClientRectangle, sf);
// Draw the border.
// Need to shrink the width and height by 1 otherwise
// there will be no border on the right or bottom.
rc = this.ClientRectangle;
rc.Width--;
rc.Height--;
Pen pen = new Pen(SystemColors.WindowFrame);
gr2.DrawRectangle(pen, rc);
// Draw from the background image onto the screen.
gr.DrawImage(DoubleBufferImage, 0, 0);
gr2.Dispose();
}
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
}

Public NotInheritable Class Win32Helper
Public Structure TRIVERTEX
Public x As Integer
Public y As Integer
Public Red As System.Int16
Public Green As System.Int16
Public Blue As System.Int16
Public Alpha As System.Int16
Public Sub New(ByVal x As Integer, ByVal y As Integer, ByVal color As Color)
MyClass.New(x, y, color.R, color.G, color.B, color.A)
End Sub
Public Sub New(ByVal x As Integer, ByVal y As Integer, ByVal red As System.Int16, ByVal green As System.Int16, ByVal blue As System.Int16, ByVal alpha As System.Int16)
Me.x = x
Me.y = y
Me.Red = CInt(red << 8)
Me.Green = CInt(green << 8)
Me.Blue = CInt(blue << 8)
Me.Alpha = CInt(alpha << 8)
End Sub
End Structure
Public Structure GRADIENT_RECT
Public UpperLeft As System.Int32
Public LowerRight As System.Int32
Public Sub New(ByVal ul As System.Int32, ByVal lr As System.Int32)
Me.UpperLeft = ul
Me.LowerRight = lr
End Sub
End Structure
Public Declare Function GradientFill Lib "coredll.dll" Alias "GradientFill" (ByVal hdc As IntPtr, _
ByVal pVertex() As TRIVERTEX, ByVal dwNumVertex As Integer, _
ByVal pMesh() As GRADIENT_RECT, ByVal dwNumMesh As Integer, _
ByVal dwMode As Integer) As Boolean
Public Const GRADIENT_FILL_RECT_H As Integer = &H0
Public Const GRADIENT_FILL_RECT_V As Integer = &H1
End Class

public sealed class Win32Helper
{
public struct TRIVERTEX
{
public int x;
public int y;
public ushort Red;
public ushort Green;
public ushort Blue;
public ushort Alpha;
public TRIVERTEX(int x, int y, Color color)
: this(x, y, color.R, color.G, color.B, color.A)
{
}
public TRIVERTEX(
int x, int y,
ushort red, ushort green, ushort blue,
ushort alpha)
{
this.x = x;
this.y = y;
this.Red = (ushort)(red << 8);
this.Green = (ushort)(green << 8);
this.Blue = (ushort)(blue << 8);
this.Alpha = (ushort)(alpha << 8);
}
}
public struct GRADIENT_RECT
{
public uint UpperLeft;
public uint LowerRight;
public GRADIENT_RECT(uint ul, uint lr)
{
this.UpperLeft = ul;
this.LowerRight = lr;
}
}
[DllImport("coredll.dll", SetLastError = true, EntryPoint = "GradientFill")]
public extern static bool GradientFill(
IntPtr hdc,
TRIVERTEX[] pVertex,
uint dwNumVertex,
GRADIENT_RECT[] pMesh,
uint dwNumMesh,
uint dwMode);
public const int GRADIENT_FILL_RECT_H = 0x00000000;
public const int GRADIENT_FILL_RECT_V = 0x00000001;
}

Private gfButton As GradientFilledButton

private GradientFilledButton gfButton;

InitializeComponent()
Me.gfButton = New GradientFilledButton()
Me.gfButton.Location = New System.Drawing.Point(71, 24)
Me.gfButton.Name = "gfButton"
Me.gfButton.Size = New System.Drawing.Size(100, 23)
Me.gfButton.TabIndex = 1
Me.gfButton.Text = "Button Test"
AddHandler Me.gfButton.Click, AddressOf Me.gfButton_Click
' Select desired start color, end color, and fill direction.
Me.gfButton.StartColor = System.Drawing.Color.SlateBlue
Me.gfButton.EndColor = System.Drawing.Color.LightCyan
gfButton.FillDirection = GradientFill.FillDirection.LeftToRight
Me.Controls.Add(gfButton)

InitializeComponent();
this.gfButton = new GradientFilledButton();
this.gfButton.Location = new System.Drawing.Point(71, 24);
this.gfButton.Name = "gfButton";
this.gfButton.Size = new System.Drawing.Size(100, 23);
this.gfButton.TabIndex = 1;
this.gfButton.Text = "Button Test";
this.gfButton.Click += new System.EventHandler(this.gfButton_Click);
// Select desired start color, end color, and fill direction.
this.gfButton.StartColor = System.Drawing.Color.SlateBlue;
this.gfButton.EndColor = System.Drawing.Color.LightCyan;
gfButton.FillDirection = GradientFill.FillDirection.LeftToRight;
this.Controls.Add(gfButton);

Private Sub gfButton_Click(ByVal sender As Object, ByVal e As System.EventArgs) 
Dim control As Control = sender
System.Diagnostics.Debug.Assert( Not (control Is Nothing))
MessageBox.Show("Clicked", "Click event handler")
End Sub

void gfButton_Click(object sender, System.EventArgs e)
{
Control control = sender as Control;
System.Diagnostics.Debug.Assert(control != null);
MessageBox.Show("Clicked", "Click event handler");
}

' Paints the background of the form with a GradientFill pattern.
Protected Overrides Sub OnPaintBackground(ByVal e As PaintEventArgs) 
' On Windows Mobile Pocket PC 2003, the call to GradientFill
' fails with GetLastError() returning 87 (ERROR_INVALID_PARAMETER)
' when e.Graphics is used.
' Instead, fill into a bitmap and then draw that onto e.Graphics.
Dim bm As New Bitmap(Width, Height)
Dim gr As Graphics = System.Drawing.Graphics.FromImage(bm)
GradientFill.Fill(gr, Me.ClientRectangle, Color.LightCyan, Color.SlateBlue, GradientFill.FillDirection.TopToBottom)
e.Graphics.DrawImage(bm, 0, 0)
gr.Dispose()
bm.Dispose()
End Sub 

// Paints the background of the form with a GradientFill pattern.
protected override void OnPaintBackground(PaintEventArgs e)
{
// On Windows Mobile Pocket PC 2003, the call to GradientFill
// fails with GetLastError() returning 87 (ERROR_INVALID_PARAMETER)
// when e.Graphics is used.
// Instead, fill into a bitmap and then draw that onto e.Graphics.
Bitmap bm = new Bitmap(Width, Height);
Graphics gr = System.Drawing.Graphics.FromImage(bm);
GradientFill.Fill(
gr,
this.ClientRectangle,
Color.LightCyan, Color.SlateBlue,
GradientFill.FillDirection.TopToBottom);
e.Graphics.DrawImage(bm, 0, 0);
gr.Dispose();
bm.Dispose();
}