User Control with custom Shape

Basically, you are using a correct approach. This is the only (valid) method of giving it a non-rectangular shape.

The only problem is: one line cannot make a valid 2D shape which could be used as a valid control region. You need to create a circular shape, not necessarily simply-conntected, but it should be a "solid" 2D shape. It means, if could be a close contour with one or more wholes in it, or something else. As an alternative to using a path made of lines, you can start with a simple base shape as rectangle or ellipse, and then add or subtract other shapes to/from it, using AND/OR set-theory operations. Please see:
http://msdn.microsoft.com/en-us/library/system.drawing.region.aspx[^].

Please see the constructors which allows you to start with a rectangle or a graphic path (as you did, only use a "solid" closed path), and then, see the methods Exclude, Union and Xor; use other methods to transform the region, and so on.

[EDIT]

As to the "line shape", there is no such thing. The closest representation of the idea would be an oblong rectangle with some finite non-zero width representing the "width of a line". It's only the mathematical abstract "line" has zero width, but, say, on-screen representation requires some width.

You can start with the rectangle, but, in general case, you need to tilt it to required angle using appropriate Transform:
http://msdn.microsoft.com/en-us/library/system.drawing.region.transform.aspx[^].

For example:

using System.Drawing;

//...

Region region = new Region(new Rectangle(x, y, width, 4));
System.Drawing.Drawing2D.Matrix shiftAndRotation = new System.Drawing.Drawing2D.Matrix();
shiftAndRotation.Rotate(requiredAngle);
shiftAndRotation.Translate(deltaX, deltaY); // shift
region.Transform = shiftAndRotation;
//...

—SA

I found in Visual Basic Power Pack a "Line Shape" and "Shape Container" this container can be used like a user control, for example:

ShapeContainer container = new ShapeContainer();
LineShape lineShape1 = new LineShape();
lineShape1.SelectionColor = this.BackColor;
lineShape1.X1 = 10;
lineShape1.X2 = 200;
lineShape1.Y1 = 30;
lineShape1.Y2 = 100;


container.Shapes.AddRange(new Microsoft.VisualBasic.PowerPacks.Shape[] {
lineShape1});

Point location = new Point();
location.X = 10;
location.Y = 20;

container.Location = location;

this.Controls.Add(container);

container.Location = location;

EDIT:

It doesn't work, because the container will no have a "Start Point and a EndPoint" will have only a Location... It will have a line shape, but still be a control, like a textbox...