How to: Display a Gradient Fill 

  • Article

You can add colorful and pleasing graphics to your application by displaying a gradient fill. The following code example shows how to display a gradient fill in a custom control and as the form's background.

Procedure

To display a gradient fill

  1. In Microsoft Visual Studio 2005, create a Smart Device Pocket PC project.

  2. Add the Gradientfill and GradientFilledButton classes to your project.

    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);
    }

}

  3. Add the Win32Helper class to your project, which contains the platform invoke and structures for native code interoperability.

    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;

}

  4. Declare a form variable named gfButton of type GradientFilledButton.

    Private gfButton As GradientFilledButton

    private GradientFilledButton gfButton;

  5. Add the following code, which initializes the gradient filled button custom control, to the constructor of the Form1 class. This code should follow the call to the InitializeComponent method. You can specify the start and ending colors of the gradient fill and either a TopToBottom or LeftToRight fill direction.

    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);

  6. Add the event handling code for the button's Click event to form.

    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");
}

  7. Override the OnPaint method to paint the background of the form with a gradient fill pattern. This code uses the GradientFill class but not the GradientFilledButton class.

    ' 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();
}

  8. Build and deploy the application.

See Also

Concepts

.NET Compact Framework How-To Topics

Other Resources

Graphics and Drawing