ToolStripRenderer Class

// This class implements a custom ToolStripRenderer for the 
// GridStrip control. It customizes three aspects of the 
// GridStrip control's appearance: GridStrip border, 
// ToolStripButton border, and ToolStripButton image.
internal class GridStripRenderer : ToolStripRenderer
{   
    // The style of the empty cell's text.
    private static StringFormat style = new StringFormat();

    // The thickness (width or height) of a 
    // ToolStripButton control's border.
    static int borderThickness = 2;

    // The main bitmap that is the source for the 
    // subimagesthat are assigned to individual 
    // ToolStripButton controls.
    private Bitmap bmp = null;

    // The brush that paints the background of 
    // the GridStrip control.
    private Brush backgroundBrush = null;

    // This is the static constructor. It initializes the
    // StringFormat for drawing the text in the empty cell.
    static GridStripRenderer()
    {
        style.Alignment = StringAlignment.Center;
        style.LineAlignment = StringAlignment.Center;
    }

    // This method initializes the GridStripRenderer by
    // creating the image that is used as the source for
    // the individual button images.
    protected override void Initialize(ToolStrip ts)
    {
        base.Initialize(ts);

        this.InitializeBitmap(ts);
    }

    // This method initializes an individual ToolStripButton
    // control. It copies a subimage from the GridStripRenderer's
    // main image, according to the position and size of 
    // the ToolStripButton.
    protected override void InitializeItem(ToolStripItem item)
    {
        base.InitializeItem(item);

        GridStrip gs = item.Owner as GridStrip;

        // The empty cell does not receive a subimage.
        if ((item is ToolStripButton) &&
            (item != gs.EmptyCell))
        {
            // Copy the subimage from the appropriate 
            // part of the main image.
            Bitmap subImage = bmp.Clone(
                item.Bounds,
                PixelFormat.Undefined);

            // Assign the subimage to the ToolStripButton
            // control's Image property.
            item.Image = subImage;
        }
    }

    // This utility method creates the main image that
    // is the source for the subimages of the individual 
    // ToolStripButton controls.
    private void InitializeBitmap(ToolStrip toolStrip)
    {
        // Create the main bitmap, into which the image is drawn.
        this.bmp = new Bitmap(
            toolStrip.Size.Width,
            toolStrip.Size.Height);

        // Draw a fancy pattern. This could be any image or drawing.
        using (Graphics g = Graphics.FromImage(bmp))
        {
            // Draw smoothed lines.
            g.SmoothingMode = SmoothingMode.AntiAlias;

            // Draw the image. In this case, it is 
            // a number of concentric ellipses. 
            for (int i = 0; i < toolStrip.Size.Width; i += 8)
            {
                g.DrawEllipse(Pens.Blue, 0, 0, i, i);
            }
        }
    }

    // This method draws a border around the GridStrip control.
    protected override void OnRenderToolStripBorder(
        ToolStripRenderEventArgs e)
    {
        base.OnRenderToolStripBorder(e);

        ControlPaint.DrawFocusRectangle(
            e.Graphics,
            e.AffectedBounds,
            SystemColors.ControlDarkDark,
            SystemColors.ControlDarkDark);
    }

    // This method renders the GridStrip control's background.
    protected override void OnRenderToolStripBackground(
        ToolStripRenderEventArgs e)
    {
        base.OnRenderToolStripBackground(e);

        // This late initialization is a workaround. The gradient
        // depends on the bounds of the GridStrip control. The bounds 
        // are dependent on the layout engine, which hasn't fully
        // performed layout by the time the Initialize method runs.
        if (this.backgroundBrush == null)
        {
            this.backgroundBrush = new LinearGradientBrush(
               e.ToolStrip.ClientRectangle,
               SystemColors.ControlLightLight,
               SystemColors.ControlDark,
               90,
               true);
        }

        // Paint the GridStrip control's background.
        e.Graphics.FillRectangle(
            this.backgroundBrush, 
            e.AffectedBounds);
    }

    // This method draws a border around the button's image. If the background
    // to be rendered belongs to the empty cell, a string is drawn. Otherwise,
    // a border is drawn at the edges of the button.
    protected override void OnRenderButtonBackground(
        ToolStripItemRenderEventArgs e)
    {
        base.OnRenderButtonBackground(e);

        // Define some local variables for convenience.
        Graphics g = e.Graphics;
        GridStrip gs = e.ToolStrip as GridStrip;
        ToolStripButton gsb = e.Item as ToolStripButton;

        // Calculate the rectangle around which the border is painted.
        Rectangle imageRectangle = new Rectangle(
            borderThickness, 
            borderThickness, 
            e.Item.Width - 2 * borderThickness, 
            e.Item.Height - 2 * borderThickness);

        // If rendering the empty cell background, draw an 
        // explanatory string, centered in the ToolStripButton.
        if (gsb == gs.EmptyCell)
        {
            e.Graphics.DrawString(
                "Drag to here",
                gsb.Font, 
                SystemBrushes.ControlDarkDark,
                imageRectangle, style);
        }
        else
        {
            // If the button can be a drag source, paint its border red.
            // otherwise, paint its border a dark color.
            Brush b = gs.IsValidDragSource(gsb) ? b = 
                Brushes.Red : SystemBrushes.ControlDarkDark;

            // Draw the top segment of the border.
            Rectangle borderSegment = new Rectangle(
                0, 
                0, 
                e.Item.Width, 
                imageRectangle.Top);
            g.FillRectangle(b, borderSegment);

            // Draw the right segment.
            borderSegment = new Rectangle(
                imageRectangle.Right,
                0,
                e.Item.Bounds.Right - imageRectangle.Right,
                imageRectangle.Bottom);
            g.FillRectangle(b, borderSegment);

            // Draw the left segment.
            borderSegment = new Rectangle(
                0,
                0,
                imageRectangle.Left,
                e.Item.Height);
            g.FillRectangle(b, borderSegment);

            // Draw the bottom segment.
            borderSegment = new Rectangle(
                0,
                imageRectangle.Bottom,
                e.Item.Width,
                e.Item.Bounds.Bottom - imageRectangle.Bottom);
            g.FillRectangle(b, borderSegment);
        }
    }
}