I don't mind so much that it is off by 0.000001 pixels. The problem is this
frame represents a user selection that can be rotated, but not rotated off
its parent (PictureBox). After rotating I validate the new coordinates to
make sure they aren't off, and negative numbers no matter how small are less
than 0. If the user has the selection at Location=(0,0), and rotates it
about (0,0), Location should still be (0,0). Rounding or floating point
precision shouldn't come into play as 0*sin(a) = 0, no matter how many digits
sin(a) is to.
I've implemented the work around below, I was just thinking it would be nice
to not create/dispose an extra GraphicsPath over and over while the user is
rotating. However it doesn't seem I can change a point of an existing
GraphicsPath.
matrix.RotateAt(m_fAngle,m_pointfPivot);
graphicspathTemp = new GraphicsPath();
graphicspathTemp.AddRectangle(m_rectanglef);
graphicspathTemp.Transform(matrix);
m_graphicspath = new GraphicsPath
(
new PointF[]
{
m_pointfPivot,
graphicspathTemp.PathPoints[1],
graphicspathTemp.PathPoints[2],
graphicspathTemp.PathPoints[3]
},
graphicspathTemp.PathTypes
);
graphicspathTemp.Dispose();
[quoted text, click to view] "Göran Andersson" wrote:
> It's just a rounding error. The Drawing classes uses single precision
> floating numbers, which have a precision of 7 digits. You simply can't
> getter better precision unless you write your own Matrix object.
>
> If the result is off by 0.000001 pixel, what is the problem really?
>
> sod0783 wrote:
> > I'm taking a rectangle and using a Matix and GraphicsPath to draw it rotated
> > about its upper left corner. The problem is GraphicsPath.Transform changes
> > the upper left point in the path slightly, so that it is no longer the same
> > as m_rectanglef.Location. This is especially a problem when
> > m_rectanglef.Location == (0,y), and comes out (-x,y) because I can't handle
> > the negatives.
> >
> > using (matrix = new Matrix())
> > {
> > matrix.RotateAt(m_fAngle,m_rectanglef.Location);
> > m_graphicspath = new
> > GraphicsPath(); m_graphicspath.AddRectangle(m_rectanglef);
> > m_graphicspath.Transform(matrix);
> > }
> >
> > Here's example coordinates:
> > m_rectanglef {X = 0.0 Y = 61.0847473 Width = 136.542374 Height = 197.028244}
> > m_fAngle -9.889401
> >
> > Before Transform:
> > m_graphicspath.PathPoints[0] {X = 0.0 Y = 61.0847473}
> >
> > After Transform:
> > m_graphicspath.PathPoints[0] {X = -0.0000007710182 Y = 61.0847435}
> >
> > Anyone else have this problem? Unfortunately I can't seem to find a way to
> > just set the path point back after Transform (PathPoints is get only). I
> > hate to create another GraphicsPath based off this one everytime, is that
> > really the only/best way?
> >
> > Thanks,
> >
> > Shawn
> >
> >
