WPF Line.Measure seems to give incorrect results

[Fred Mellender]

I have a vertical line going from (20,0) to (20,-200):


CODE:
Line foo = new Line();
foo.X1 = 20;
foo.Y1 = 0;
foo.X2 = 20;
foo.Y2 = -200;

foo.StrokeThickness = 4;
foo.Stroke = Brushes.Black;

foo.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
Size fooSize = foo.DesiredSize;
bool valid = foo.IsMeasureValid;

RESULTS:
valid is true and
fooSize is:
fooSize.height = 0.0;
fooSize.width = 22.0 (twenty-two)

I was expecting height = 200, width = 4.

Can someone explain how else I can get the bounding box of a line (or other
UIElement), and what DesiredSize is returning?

I am trying to work in world coordinates and need the various bounding boxes
of the UIElements
that I will add to a canvas, so that I can scale the entire canvas to a
containing panel, (via a transform).
It all works well if I calculate the bounding boxes myself but I wanted
something more general.

 

[not_a_commie]

The Line object will have an ActualWidth, ActualHeight members that
give the sizes after Measure and Arrange have been called. And have
you considered doing your scaling with matrix transforms?

 

[Fred Mellender]

I wanted to calculate the matrix transforms before Measure and Arrange have
been called. I am trying to scale
the panel, world, (and thus its contents) based on examining all its
childrens' width/height and position.

The code I am using is:

foreach (UIElement s in world.Children)
{
double top = 0, bottom = 0, left = 0, right = 0;

s.Measure(new Size(double.PositiveInfinity,
double.PositiveInfinity));
Size elementSize = s.DesiredSize;

Line line = s as Line;

if (line != null)
{
top = Math.Max(line.Y1, line.Y2);
left = Math.Min(line.X1, line.X2);
bottom = Math.Min(line.Y1, line.Y2);
right = Math.Max(line.X1, line.X2);

//bottom = top - elementSize.Height;
//right = left + elementSize.Width;
}

else ....... //etc for other objects.....

maxX = Math.Max(right, maxX);
maxY = Math.Max(top, maxY);
minX = Math.Min(left, minX);
minY = Math.Min(bottom, minY);
}

double maxWidth = maxX - minX;
double maxHeight = maxY - minY;

world.Measure(new Size(double.PositiveInfinity,
double.PositiveInfinity));
Size size = world.DesiredSize;

double scaleX = graphicPanel.ActualWidth / maxWidth;
double scaleY = -graphicPanel.ActualHeight / maxHeight;

ScaleTransform transS = new ScaleTransform(scaleX, scaleY);
ScaleTransform transS = new ScaleTransform(scaleX, scaleY);
TranslateTransform transT = //since we
translate after scaling, we must scale the translate first
new TranslateTransform(-minX * Math.Abs(scaleX), maxY *
Math.Abs(scaleY));

TransformGroup group = new TransformGroup();
group.Children.Add(transS);
group.Children.Add(transT);

graphicPanel.RenderTransform = group;

The commented lines are what I wanted to use for bottom/right.

I do not understand why the elementSize.Height/Width are not accurate, or
what the
values they are set to, mean.