[2008] Creating a finer Pen

[user name]

I am working on a part of an application that requires a graph which i have done using a picturebox and CreateGraphics.DrawLine, it accepts scores which there could be between 20 and 45 scores to show on the graph across the width of the picturebox. My question is, can we draw a line with a finer pen so the diagonal lines dont look to jagged (see pictures).

20 scores is probably ok but when it accepts 45 it looks a bit dodgy.

[RobDog888]

A Pens width can only be as small as 1. You could add AntiAliasing smoothing so its not all jaggged.

System.Drawing.Drawing2D.SmoothingMode.AntiAlias as well as System.Drawing.Drawing2D.SmoothingMode.HighQuality

[jmcilhinney]

Please tell me that you haven't actually used CreateGraphics.DrawLine in your code. If you ever do call CreateGraphics, which should be a very, VERY rare thing, then you need to keep a reference to the Graphics object it creates so that you can dispose it, which you should almost always do with a Using block:

Using g As Graphics = myControl.CreateGraphics()
    'Use g here.
End Using

The reason that you should almost never need to call CreateGraphics is that you should do all your drawing in the Paint event handler or OnPaint method of the control, which already has a Graphics object provided via the PaintEventArgs object you get from the 'e' parameter.

[user name]

It sounds like i am doing this completely wrong, the code as follows is a sub within a module that accepts the picturebox, maximum score and the scores. Could you point out what i shouldnt be doing.

I am not being ignorant by not replying straight away, i need to go offline until tomorrow, thanks for having a look.

 Public Sub GraphSub(ByVal pb As PictureBox, ByVal pbMaxH As Integer, ByVal Scores As Integer())

        Dim MaxSplit As Double, WidSplit As Double, ScH As Double
        Dim LastPoint As New Point
        Dim LastX As Integer, LastY As Integer

        pb.CreateGraphics.Clear(pb.BackColor)
        MaxSplit = pb.Height / pbMaxH

        For i As Integer = 0 To Scores.GetUpperBound(0)

            ScH = Scores(i) * MaxSplit
            WidSplit = Math.Round((pb.Width - LastPoint.X) / ((Scores.Length + 1) - i))

            LastPoint.X = CInt(LastPoint.X + WidSplit)
            LastPoint.Y = CInt(Math.Round(pb.Height - ScH))

            pb.CreateGraphics.DrawLine(Pens.Red, LastPoint.X, LastPoint.Y, LastPoint.X, pb.Height)
            pb.CreateGraphics.DrawRectangle(Pens.Red, LastPoint.X - 2, LastPoint.Y - 2, 4, 4)

            pb.CreateGraphics.DrawLine(Pens.Blue, LastX, LastY, LastPoint.X, LastPoint.Y)

            LastY = LastPoint.Y
            LastX = LastPoint.X

        Next

    End Sub

[jmcilhinney]

You're calling CreateGraphics four times, so you are creating four different Graphics objects and disposing none of them. That's a resource leak right there. Apart from that, the fact that you're not doing your drawing on the Paint event of the PictureBox means that, as soon as the PictureBox gets repainted, like when it's minimised and restored, your graph will simply disappear.

What you need to do is store all the variable data for the drawing in member variables somewhere. When you want to draw the graph you set those variables if they haven't been set already and then force the Picturebox to repaint itself by calling its Refresh method. That will raise the PictureBox's Paint event and you do your drawing in the PictureBox's Paint event handler.

Follow the Simple Drawing link in my signature for an example.

[user name]

Thank you for your time, ill look into that.