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The custom windows procedure.

protected override void WndProc(ref Message m)

{

//calculate the maximum size of the non-client border area

//3 is the minimum because the border is 3 pizels wide

int bmax=(int)Math.Max(3,_borderRadius);

//0.41 is a fudge factor. A square of approximately 0.82*diameter will fit neatly into a circle

//with diameter of 1 so 0.41 is half of the diameter

int adustedbmax=(int)Math.Max(3,0.40*bmax);

switch(m.Msg)

{

case (int)WmDefs.WM_NCCALCSIZE:

if ((int)m.WParam == 0)

{

//Shrink the window rect to create the client rect

RECT rc=(RECT)Marshal.PtrToStructure(m.LParam,typeof(RECT));

rc.left+=adustedbmax;

rc.top+=adustedbmax ;

rc.right-=adustedbmax ;

rc.bottom-=adustedbmax ;

Marshal.StructureToPtr(rc,m.LParam,false);

m.Result=IntPtr.Zero;

}

break;

case (int)WmDefs.WM_NCPAINT:

{

//get the window DC

IntPtr dc=GetWindowDC(m.HWnd);

//and the window rectangle in screen coordinates

RECT rc=new RECT();

GetWindowRect(m.HWnd,ref rc);

//convert to a GDI+ rectangle and translate to client coordinates

Rectangle r=new Rectangle(rc.left,rc.top,rc.right-rc.left,rc.bottom-rc.top);

r=this.RectangleToClient(r);

//because the rectangle origin is negative with respect to the client area

//we offset the rectangle so that it fits into the WindowDC correctly

r.Offset(adustedbmax,adustedbmax);

//Create a rectangle that is the right size for the border. 3 pixels smalller than the window DC

Rectangle rcBorder=r;

rcBorder.Width-=3;

rcBorder.Height-=3;

//Get a graphics for the WindowDC

Graphics g=Graphics.FromHdc(dc);

//the client rectangle and the window rectangle are used to make a region

//that includes the border but excludes the client area to reduce potential flicker

Rectangle r2=this.ClientRectangle;

r2.Offset(adustedbmax,adustedbmax);

Region rg=new Region(r);

rg.Exclude(r2);

//the clipping region is set to include only the non-client area

g.SetClip(rg,CombineMode.Replace);

g.Clear(BackColor);

//Now a 3 pixel 3D shaded border is drawn using

//3 overlapping round-rectangles

Pen p=new Pen(Color.White,1);

g.SmoothingMode=SmoothingMode.AntiAlias;

//#1

RoundRect(g, p, rcBorder, bmax);

p.Color=Color.Gray;

rcBorder.Offset(2,2);

//#2

RoundRect(g, p, rcBorder, bmax);

p.Color=Color.Black;

rcBorder.Offset(-1,-1);

//#3

RoundRect(g, p, rcBorder, bmax);

//clean up.

p.Dispose();

g.Dispose();

ReleaseDC(m.HWnd,dc);

//signal success

m.Result=IntPtr.Zero;

}

break;

default:

base.WndProc(ref m);

break;

}

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