How to make a line drawn by graphics selectable in .NET

Question

A simple code for drawing a line.

using (Graphics g = this.CreateGraphics())
        {
            g.DrawLine(Pens.Black, new Point(50, 50), new Point(100, 100));
        }

This will draw a typical line. However i want to this line to be selectable so that user can manipulate it further(streching, resizing etc) at run time. Initially i attempted to use controls that can be manipulated at runtime with the line as background however that could not work due to overlapping controls issue.

My question is how can i select this line at runtime ?

Answer 1

You need to write it yourself.

1. Write a class that wraps Line
2. Add all needed additional behavior to the class (what happens when the line is selected, what happens when the line is stretched, deleted, changed color ...)
3. Write a class that manages either object was was picked by mouse or not (RayTracer)

etc...

Or simply use: piccolo2d framework

Structured 2D Graphics Framework

Answer 2

I think what you're looking to do is make the Graphics object to be selectable? If so, you could put your logic into the MouseOver and MouseButton events. Check this out, it may give you some insight.

Selectable Graphics Object

Answer 3

You must create it yourself. Declare interfaces that your graphics objects implement. Suggestion:

public interface IObject
{
    bool HitTest(Point mouseLocation);
    void Paint(Graphics g);
    List<IAdorner> Adorners { get; }
}

public interface IAdorner
{
    bool HitTest(Point mouseLocation);
    void Paint(Graphics g);

    void StartMoving(Point mouseLocation);
    void Move(Point mouseLocation);
}

The adorners are the selectable end points of a line object for instance.

Your main paint routine will look something like this:

private void drawingSurface_Paintobject sender, PaintEventArgs e)
{
    foreach (IObject o in _objects) {
        o.Paint(e.Graphics);
        if (o == _selectedObject) {
            foreach (IAdorner a in o.Adorners) {
                a.Paint(e.Graphics);
            }
        }
    }
}

And of cause you need all the mouse event handling.

These interfaces are abstract enough in order to allow the implementation of any shapes. For instance they don't include any coordinates, as different types of objects need different numbers and kinds of coordinates and parameters.

Answer 4

Maybe It's a little too late, since you already accepted an answer, but you should really consider WPF for this.

https://stackoverflow.com/a/15469477/643085

That's an exact sample of what you're after, in WPF + MVVM. With a real whole LOT of advantages over any winforms approach (such as NO flicker due to hardware acceleration).

Please at least give it a try. Full CSProj project Source available.

You're REALLY reiventing the wheel implementing all this yourself in GDI. And in the end it will be unusable due to flickering and stuff like that.