Regions, Ellipses and Intersect Problem (maybe a bug?)

Intersect method of a Region means to update the region data with its intersection with another Region, GraphicsPath, Rectangle, or RectangleF. If the second object is totally inside the region then its intersect bounds shoud be exactly the same as the object itself (at least thats what I think). But this is not true with ellipses and regions, as the Y of the intersect region is 1 more than the Y of the ellipse and its height is one less, but X and Width are the same. That does not happen for Rectanlges. Try the following codes to see what I mean.

VB Code:

Dim gPath As New Drawing.Drawing2D.GraphicsPath
gPath.AddEllipse(New RectangleF(3, 3, 10, 10))
Dim rg As New Region(New RectangleF(0, 0, 20, 20))
rg.Intersect(gPath)
MessageBox.Show(rg.GetBounds(Me.CreateGraphics).Equals(gPath.GetBounds))

Returns False

VB Code:

Dim gPath As New Drawing.Drawing2D.GraphicsPath
gPath.AddRectangle(New RectangleF(3, 3, 10, 10))
Dim rg As New Region(New RectangleF(0, 0, 20, 20))
rg.Intersect(gPath)
MessageBox.Show(rg.GetBounds(Me.CreateGraphics).Equals(gPath.GetBounds))

Returns True

VB Code:

Dim gPath As New Drawing.Drawing2D.GraphicsPath
gPath.AddEllipse(New RectangleF(3, 3, 10, 10))
Dim rec As New RectangleF(0, 0, 20, 20)
MessageBox.Show(RectangleF.Intersect(rec, gPath.GetBounds).Equals(gPath.GetBounds))

Returns True

VB Code:

Dim gPath As New Drawing.Drawing2D.GraphicsPath
gPath.AddRectangle(New RectangleF(3, 3, 10, 10))
Dim rec As New RectangleF(0, 0, 20, 20)
MessageBox.Show(RectangleF.Intersect(rec, gPath.GetBounds).Equals(gPath.GetBounds))

Returns True

No idea?

Hmm you sure seem to have studied the problem...
I have stumbled over this issue too. i used addarc (x 4, 1 for each corner) to create a path the shape of a rectangle with rounded corners. i filled my path and then i used drawpath method to draw an outline. my problem is that when i use this path as region for my control the outline is clipped especially in the corners area. have you found any workaround for getting the exact intersection ?

Well, I still think that is a bug. I posted the question to MSDN newsgroup and didn't get anything back and now that I am checking the messages there, it seems they only keep messages of last three months or so and my message was not there at all.

for your problem, try using Widen method of Graphicspath and see if that corrects your problem, becuase I guess the outline is not considered inside the graphicspath, you know what I mean?

Hi,

I don't really have a clue as to what you guys are talking about, but I do work with elipses. I have to calculate the voulme of liquid remaining in eliptical tanks, which necessitates calculating the area of an elipse lying below a given horizontal line. If that formula is of any use to you I can post it.

You might find your question answered in

www.mathforum.org/dr.math