BUG in GDI whit zoom ?

[davide rocchelli]

I have found a probable bug when you draw with GDI.
Look this simple code

Private Sub Form1_Paint(ByVal sender As Object, ByVal e
As System.Windows.Forms.PaintEventArgs) Handles
MyBase.Paint

Const Zoom As Single = 0.001
Dim p As Pen

'line incriminate
e.Graphics.SmoothingMode =
Drawing2D.SmoothingMode.AntiAlias

'clear
e.Graphics.Clear(Color.Black)
'zoom
e.Graphics.ScaleTransform(Zoom, Zoom)
'create a pen
p = New Pen(Color.Red, 1)
p.DashPattern = New Single() {5, 5}
'draw line (adjusted to zoom)
e.Graphics.DrawLine(p, (Me.ClientRectangle.Left /
Zoom), (Me.ClientRectangle.Top / Zoom),
(Me.ClientRectangle.Right / Zoom),
(Me.ClientRectangle.Bottom / Zoom))
End Sub

If you set SmoothingMode to AntiAlias or HighQuality the
line is ok: the dash pattern is what you want. But if you
set SmoothingMode to another value, the pattern is
oscene, idem if you set p.DashStyle = DashStyle.Dash (or
other value except Solid) without use DashPattern. If
yout don't use the zoom (ScaleTransform) you have no
problem.

With personal Pattern you must do this to have the
desired pattern

p.DashPattern = New Single() {5 / Zoom, 5 / Zoom}

but if you use this line with e.Graphics.SmoothingMode =
Drawing2D.SmoothingMode.AntiAlias (or HightQuality) the
line's style is obsene.

The right action is with
Drawing2D.SmoothingMode.AntiAlias: if I set thath i want
a line, I want a line, not a trash 'cause i make a
zoom ...

Suggestion ? I must calculate then pattern depending the
quality, and this not good ...

Davide.