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How to: Display a Gradient Fill

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

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 Visual Studio, create a Smart Device 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 in the .NET Compact Framework