Why so much trouble with ellipses?

[Nathan Sokalski]

In a recent post of mine I mentioned the inaccurate shapes drawn by
FillEllipse. In the response that I recieved I was told that DrawArc had
less problems, which I found to be true (I have been using DrawEllipse, but
they seem to have the same results when drawing a complete 360). However,
even with these methods, there are situations where the results are not even
symmetric along both axes (my best example of this is with a width and
height of 6). I know enough about math and computers to be able to figure
out how to write a simple method to create a basic circle or ellipse, so I'm
not going to ask anyone to tell me how to fix it (even though that would be
nice), but I am going to ask why couldn't Microsoft make this simple method
themselves? It's not like this is the first time they ever had to do it.
Heck, they could have just borrowed some code from Paint, I know that that
makes correct circles/ellipses. Do they plan to fix this in a future
version, or is GDI+ such a small part of .NET that they don't care? (I will
admit that I am guilty of still using .NET 1.1, but I still think it should
have been a simple enough task that they could have done it right by now).
What do all of you think?

 

[Cor Ligthert [MVP]]

Nathan,

You make me curious I see a lot of crossposting adresses. Feel free to do
that.

The in my idea real newsgroup for this question

microsoft.public.dotnet.framework.drawing

is not in it.

What is the reason for that?

Cor

 

[Nathan Sokalski]

I am not currently subscribed to that newsgroup, so I guess I forgot to post
to it. But now that I know about it, I guess it would be one of, if not the,
best group for my question. Thanks.

 

[Peter Proost]

Hi Nathan

these two thing should help you, you don't need to use them both, it seems
to me that setting the g.SmoothingMode gives better results.

g.PixelOffsetMode = Drawing2D.PixelOffsetMode.Half

g.SmoothingMode = Drawing2D.SmoothingMode.HighQuality

Greetz Peter

 

[Nathan Sokalski]

I tried all of the settings for each of these, but none of them made
ellipses with a radius of 6 the same on all sides, the closest ones were the
same as not setting the settings at all. I am assuming that this would be
true for other radii as well, but since DrawEllipse already gave me good
ellipses for all the radii I tried, I didn't bother testing anything other
than 6. In other words, back to the System.Drawing board.

 

[Peter Proost]

Hi Nathan,

if I add g.SmoothingMode = Drawing2D.SmoothingMode.HighQuality to the sample
I posted a couple of days ago, I get nice ellipses with drawellipse and
fillellipse for all radii from 4 to 14 (haven't tested any further)

Grtz Peter

 

[Peter Proost]

Here's the example again because it wasn't origanly posted in this thread

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
Dim myBmp As New Bitmap(450, 450)
Dim g As Graphics
g = Graphics.FromImage(myBmp)
g.Clear(Color.Black)
g.SmoothingMode = Drawing2D.SmoothingMode.HighQuality
Dim posX As Integer = 10
Dim myWidth, myHeight As Integer
myWidth = 4
myHeight = 4
For i As Integer = 0 To 21
If i <= 10 Then
drawCircles(g, 0, posX, myWidth, myHeight)
Else
drawCircles(g, 1, posX, myWidth, myHeight)
End If
posX += 20
myWidth += 1
myHeight += 1
If i = 10 Then
myWidth = 4
myHeight = 4
End If
Next
g.Dispose()
PictureBox1.Image = myBmp
myBmp.Save("c:\testEllipse.bmp", Drawing.Imaging.ImageFormat.Bmp)
MsgBox("c:\testEllipse.bmp Saved", MsgBoxStyle.Information, "Saved")


End Sub

Private Sub drawCircles(ByVal g As Graphics, ByVal drawType As Integer,
ByVal x As Integer, ByVal width As Integer, _ ByVal _ height As Integer)
Dim intY As Integer = 5
For i As Integer = 0 To 20
Select Case drawType
Case 0
g.FillEllipse(Brushes.LawnGreen, x, intY, width, height)
Case 1
g.DrawEllipse(Pens.LawnGreen, x, intY, width, height)
End Select
intY += 18
Next
End Sub

Greetz Peter