The following will work in XP, I have no Vista machine handy to test it, but I think you're issues are steming from an incorrect hWnd somehow. Anyway, on with the poorly commented code.
// The state of our little button
ButtonState _buttState = ButtonState.Normal;
Rectangle _buttPosition = new Rectangle();
[DllImport("user32.dll")]
private static extern IntPtr GetWindowDC(IntPtr hWnd);
[DllImport("user32.dll")]
private static extern int GetWindowRect(IntPtr hWnd,
ref Rectangle lpRect);
[DllImport("user32.dll")]
private static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);
protected override void WndProc(ref Message m)
{
int x, y;
Rectangle windowRect = new Rectangle();
GetWindowRect(m.HWnd, ref windowRect);
switch (m.Msg)
{
// WM_NCPAINT
case 0x85:
// WM_PAINT
case 0x0A:
base.WndProc(ref m);
DrawButton(m.HWnd);
m.Result = IntPtr.Zero;
break;
// WM_ACTIVATE
case 0x86:
base.WndProc(ref m);
DrawButton(m.HWnd);
break;
// WM_NCMOUSEMOVE
case 0xA0:
// Extract the least significant 16 bits
x = ((int)m.LParam << 16) >> 16;
// Extract the most significant 16 bits
y = (int)m.LParam >> 16;
x -= windowRect.Left;
y -= windowRect.Top;
base.WndProc(ref m);
if (!_buttPosition.Contains(new Point(x, y)) &&
_buttState == ButtonState.Pushed)
{
_buttState = ButtonState.Normal;
DrawButton(m.HWnd);
}
break;
// WM_NCLBUTTONDOWN
case 0xA1:
// Extract the least significant 16 bits
x = ((int)m.LParam << 16) >> 16;
// Extract the most significant 16 bits
y = (int)m.LParam >> 16;
x -= windowRect.Left;
y -= windowRect.Top;
if (_buttPosition.Contains(new Point(x, y)))
{
_buttState = ButtonState.Pushed;
DrawButton(m.HWnd);
}
else
base.WndProc(ref m);
break;
// WM_NCLBUTTONUP
case 0xA2:
// Extract the least significant 16 bits
x = ((int)m.LParam << 16) >> 16;
// Extract the most significant 16 bits
y = (int)m.LParam >> 16;
x -= windowRect.Left;
y -= windowRect.Top;
if (_buttPosition.Contains(new Point(x, y)) &&
_buttState == ButtonState.Pushed)
{
_buttState = ButtonState.Normal;
// [[TODO]]: Fire a click event for your button
// however you want to do it.
DrawButton(m.HWnd);
}
else
base.WndProc(ref m);
break;
// WM_NCHITTEST
case 0x84:
// Extract the least significant 16 bits
x = ((int)m.LParam << 16) >> 16;
// Extract the most significant 16 bits
y = (int)m.LParam >> 16;
x -= windowRect.Left;
y -= windowRect.Top;
if (_buttPosition.Contains(new Point(x, y)))
m.Result = (IntPtr)18; // HTBORDER
else
base.WndProc(ref m);
break;
default:
base.WndProc(ref m);
break;
}
}
private void DrawButton(IntPtr hwnd)
{
IntPtr hDC = GetWindowDC(hwnd);
int x, y;
using (Graphics g = Graphics.FromHdc(hDC))
{
// Work out size and positioning
int CaptionHeight = Bounds.Height - ClientRectangle.Height;
Size ButtonSize = SystemInformation.CaptionButtonSize;
x = Bounds.Width - 4 * ButtonSize.Width;
y = (CaptionHeight - ButtonSize.Height) / 2;
_buttPosition.Location = new Point(x, y);
// Work out color
Brush color;
if (_buttState == ButtonState.Pushed)
color = Brushes.LightGreen;
else
color = Brushes.Red;
// Draw our "button"
g.FillRectangle(color, x, y, ButtonSize.Width, ButtonSize.Height);
}
ReleaseDC(hwnd, hDC);
}
private void Form1_Load(object sender, EventArgs e)
{
_buttPosition.Size = SystemInformation.CaptionButtonSize;
}