System.​Drawing and others in C#

I am currently working on an application, and one of its features uses the following code:

private void Form1_MouseMove(object sender, MouseEventArgs e)

if (e.Button == MouseButtons.Left)

System.Drawing.Pen myPen;

myPen = new System.Drawing.Pen(System.Drawing.Color.Red, 3);

System.Drawing.Graphics formGraphics = this.CreateGraphics();

else

Record the position at last mousemove event and draw a line from that point to the new point, that way you'll get a continuous line.

private void Picture_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e) {

if (e.Button == MouseButtons.Left) {

_drawing = true;

_lastPoint = new Point(e.X, e.Y);

this.MouseMove += new System.Windows.Forms.MouseEventHandler(this.Picture_MouseMove);

this.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Picture_MouseUp);

}

}

private void Picture_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e) {

if (_drawing) {

Point newPoint = new Point(e.X, e.Y);

DrawLine(_lastPoint, newPoint);

_lastPoint = newPoint;

}

}

private void Picture_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e) {

if (e.Button == MouseButtons.Left) {

this.MouseUp -= new System.Windows.Forms.MouseEventHandler(this.Picture_MouseUp);

this.MouseMove -= new System.Windows.Forms.MouseEventHandler(this.Picture_MouseMove);

if (_drawing) {

Point newPoint = new Point(e.X, e.Y);

DrawLine(_lastPoint, newPoint);

}

_drawing = false;

}

}

private void DrawLine(Point from, Point to) {

Graphics g = this.CreateGraphics();

using (Pen p = new Pen(Color.Black)) {

g.DrawLine(p, from, to);

}

}

OK, i'm adding to the original question; Shouldn't all drawing be done in the OnPaint() event?
If so, how would you implement this program properly?
If not, is the code below legal/proper in every way?
Also, the code below does not handle rezising/minimizing of the window, what is the best way to fix that?
Here's How I got it to work, just paste it onto a form with the appropriate eventhandlers declared (Based on mule's code):

bool _drawing = false;
Point _lastPoint;
Point _newPoint;
private void Form1_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        //Are these really necessary?
        //this.MouseUp -= new //System.Windows.Forms.MouseEventHandler(this.Picture_MouseUp);
        //this.MouseMove -= new //System.Windows.Forms.MouseEventHandler(this.Picture_MouseMove);

        if (_drawing)
        {
            _newPoint = new Point(e.X, e.Y);
            DrawLine(_lastPoint, _newPoint, this.CreateGraphics());
        }
        _drawing = false;
    }
}

private void Form1_MouseMove(object sender, MouseEventArgs e)
{
    if (_drawing)
    {
        _lastPoint = _newPoint;
        _newPoint = new Point(e.X, e.Y);
        DrawLine(_lastPoint, _newPoint, this.CreateGraphics());
    }
}

private void Form1_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        _drawing = true;
        _lastPoint = new Point(e.X, e.Y);
        _newPoint = new Point(e.X, e.Y);

        //Again, are these really neccesary?
        //this.MouseMove += new  //System.Windows.Forms.MouseEventHandler(this.Picture_MouseMove);
        //this.MouseUp += new //System.Windows.Forms.MouseEventHandler(this.Picture_MouseUp);

    }
}

private void DrawLine(Point from, Point to)
{
    Graphics g = this.CreateGraphics();
    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
    Pen p = new Pen(Color.Red, 5);//Just to make it look nice
    p.StartCap = System.Drawing.Drawing2D.LineCap.Round;//Just to make it look nice
    p.EndCap = System.Drawing.Drawing2D.LineCap.Round;//Just to make it look nice
    g.DrawLine(p, from, to);
    g.Dispose();
    p.Dispose();
}

Shouldn't all drawing be done in the OnPaint() event?

Not necessarily.  The OnPaint event is for handling the drawing of the control itself. If you want to draw on a surface in your application, then you can create a Graphics object anytime you like. As I understand it.


If not, is the code below legal/proper in every way?

Legal? I don't think it commits any cardinal sins.

Also, the code below does not handle rezising/minimizing of the window, what is the best way to fix that?

What are you trying to achive?  Are you trying to write a simple paint program?

That's going to be a lot more work. Firstly you are going to have to set what the size of the image you're creating is, and keep a bitmap of everything you've drawn to the surface each time it changes - keep a history of say 8 of these for undos. You should then be repainting that bitmap when you resize / restore from minimized.