C# Form with custom border and rounded edges [duplicate]

Answer 1

The Region propery simply cuts off the corners. To have a true rounded corner you will have to draw the rounded rectangles.

Drawing rounded rectangles

It might be easier to draw an image of the shape you want and put that on the transparent form. Easier to draw but cannot be resized.

Answer 2

Note you're leaking the handle returned by CreateRoundRectRgn(), you should free it with DeleteObject() after it is used.

The Region.FromHrgn() copies the definition, so it won't free the handle.

[DllImport("Gdi32.dll", EntryPoint = "DeleteObject")]
public static extern bool DeleteObject(IntPtr hObject);

public Form1()
{
    InitializeComponent();
    IntPtr handle = CreateRoundRectRgn(0, 0, Width, Height, 20, 20);
    if (handle == IntPtr.Zero)
        ; // error with CreateRoundRectRgn
    Region = System.Drawing.Region.FromHrgn(handle);
    DeleteObject(handle);
}

(would add as comment but reputation is ded)