AlphaColorPanel.cs

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace CaravelEditor
{

    public class AlphaColorPanel : Panel {

	    public event EventHandler AlphaChanged;

	    NumericUpDown nudAlpha = new NumericUpDown { AutoSize = true, Minimum = 0, Maximum = 255, DecimalPlaces = 0, Increment = 1, Value = 255, Anchor = AnchorStyles.Top };
	    TrackBar trackBar = new TrackBar2 { Minimum = 0, Maximum = 255, TickFrequency = 5, TickStyle = TickStyle.None, Orientation = Orientation.Horizontal, Value = 255, Anchor = AnchorStyles.Left | AnchorStyles.Right };
	    Color[] colors = new Color[] { Color.White, Color.Black, Color.Green, Color.Blue, Color.Red, Color.Yellow };
	    public int Cols { get; set; }
	    public int SwatchSize { get; set; }

	    private Color color = Color.Empty;

	    public AlphaColorPanel() : base() {
		    Dock = DockStyle.Fill;
		    AutoSize = true;
		    AutoSizeMode = AutoSizeMode.GrowAndShrink;
		    DoubleBuffered = true;
		    //TabStop = true;
		    //SetStyle(ControlStyles.Selectable, true);
		    ResizeRedraw = true;

		    Cols = 3;
		    SwatchSize = 100;
		    trackBar.ValueChanged += trackBar_ValueChanged;
		    nudAlpha.ValueChanged += nudAlpha_ValueChanged;
		    Alpha = 255;

		    TableLayoutPanel p = new TableLayoutPanel { Dock = DockStyle.Bottom };
		    p.AutoSize = true;
		    p.AutoSizeMode = AutoSizeMode.GrowAndShrink;
		    p.Controls.Add(nudAlpha, 0, 0);
		    p.Controls.Add(trackBar, 1, 0);
		    p.ColumnStyles.Add(new ColumnStyle(SizeType.AutoSize));
		    p.ColumnStyles.Add(new ColumnStyle(SizeType.Percent, 1));
		    Controls.Add(p);

		    nudAlpha.KeyDown += nudAlpha_KeyDown;
		    trackBar.KeyDown += trackBar_KeyDown;
	    }

	    void trackBar_KeyDown(object sender, KeyEventArgs e) {
		    HandleKeyEvent((Control) sender, e);
	    }

	    void nudAlpha_KeyDown(object sender, KeyEventArgs e) {
		    HandleKeyEvent((Control) sender, e);
	    }

	    private void HandleKeyEvent(Control sender, KeyEventArgs e) {
		    if (e.KeyCode == Keys.Enter) {
			    e.SuppressKeyPress = true; // stop beep
			    e.Handled = true;
		    }
		    else if (e.KeyCode == Keys.Escape) {
			    e.SuppressKeyPress = true;
			    e.Handled = true;
			    Form f = FindForm();
			    if (f != null)
				    f.Close();
		    }
		    else if (e.KeyCode == Keys.Tab) {
			    // seems like because the Form is displays with Show(Window) but
			    // it is not modal, that stops tabs from working correctly, so
			    // it is handled manually:
			    sender.Parent.SelectNextControl(sender, true, true, true, true);
			    e.SuppressKeyPress = true;
			    e.Handled = true;
		    }
	    }

	    void nudAlpha_ValueChanged(object sender, EventArgs e) {
		    trackBar.Value = Convert.ToInt32(nudAlpha.Value);
	    }

	    public override Size GetPreferredSize(Size proposedSize) {
		    int w = SwatchSize * Cols;
		    int h = SwatchSize * (((Colors.Length - 1) / Cols) + 1);
		    h += Math.Max(trackBar.Height, nudAlpha.Height);
		    return new Size(w, h);
	    }

	    public Color Color {
		    get {
			    return color;
		    }
		    set {
			    var c = value;
			    color = Color.FromArgb(Alpha, c.R, c.G, c.B);
			    Invalidate(); //Refresh();
		    }
	    }

	    public int Alpha {
		    get {
			    return trackBar.Value;
		    }
		    set {
			    trackBar.Value = value;
		    }
	    }

	    public Color[] Colors {
		    get {
			    return colors;
		    }
		    set {
			    colors = value;
		    }
	    }

	    void trackBar_ValueChanged(object sender, EventArgs e) {
		    nudAlpha.Value = trackBar.Value;
		    Color c = Color;
		    Color = Color.FromArgb(trackBar.Value, c.R, c.G, c.B);
		    Refresh();
		    if (AlphaChanged != null)
			    AlphaChanged(this, EventArgs.Empty);
	    }

	    protected override void OnPaint(PaintEventArgs e) {
		    base.OnPaint(e);

		    int rows = ((Colors.Length - 1) / Cols) + 1;
		    int r1 = Width / Cols;
		    int r2 = Height / Cols;
		    int r = Math.Min(r1, r2);
		    if (r < SwatchSize)
			    r = SwatchSize;

		    int offsetX = (Width - r * Cols) / 2;
		    int offsetY = ((Height - Math.Max(nudAlpha.Height, trackBar.Height)) - r * rows) / 2;

		    var g = e.Graphics;
		    int x = 0;
		    int y = 0;
		    for (int i = 0, j = 1; i < colors.Length; i++, j++) {
			    Color c = colors[i];

			    using (var b = new SolidBrush(c))
				    g.FillRectangle(b, x + offsetX, y + offsetY, r, r);

			    if (j == Cols) {
				    j = 0;
				    x = 0;
				    y += r;
			    }
			    else {
				    x += r;
			    }
		    }

		    using (var b = new SolidBrush(Color))
			    g.FillRectangle(b, r / 2 + offsetX, r / 2 + offsetY, 2 * r, r);
	    }
    }


    class TrackBar2 : TrackBar {

	    public TrackBar2() : base() {
		    AutoSize = false;
		    RECT r = GetThumbRect(this);
		    Height = r.Bottom - r.Top;
	    }

	    public override Size GetPreferredSize(Size proposedSize) {
		    Size sz = base.GetPreferredSize(proposedSize);
		    RECT r = GetThumbRect(this);
		    sz.Height = r.Bottom - r.Top;
		    return sz;
	    }

	    [StructLayout(LayoutKind.Sequential)]
	    private struct RECT {
		    public int Left;
		    public int Top;
		    public int Right;
		    public int Bottom;
	    }

	    [DllImport("user32.dll")]
	    private static extern void SendMessage(IntPtr hwnd, uint msg, IntPtr wp, ref RECT lp);

	    private const uint TBM_GETTHUMBRECT = 0x419;
	    private static RECT GetThumbRect(TrackBar trackBar) {
		    RECT rc = new RECT();
		    SendMessage(trackBar.Handle, TBM_GETTHUMBRECT, IntPtr.Zero, ref rc);
		    return rc;
	    }
    }


}