Handle without scaling in GDI +

Question

I need to create a pen that draws with a width of 0.5 mm regardless of the scale of the graphics transformation matrix. That's what I'm doing:

Note: The sample code is C ++ / CLI, but responses using C # are welcome.

// assume that g is a Graphics object
int dpi = g->DpiX;
float dotsPerHalfInch = dpi * 0.5;

// to extract scale factor from the transformation matrix...
// create two points distant one unit apart...
array<PointF> ^points = gcnew array<PointF>{
    PointF(0.0f, 0.0f), PointF(1.0f, 0.0f)
};

// transform them...
g->Transform->TransformPoints(points);

// get distance after transformation...
float dX = points[1].X - points[0].X;
float dY = points[1].Y - points[0].Y;
float distance = Math::Sqrt(dX * dX + dY * dY);

// reverse the effects of any scale factor in graphics transform
float penWidth = dotsPerHalfInch / distance;

Pen ^halfInchPen = gcnew Pen(Color::Black, penWidth);

It doesn't seem to work on the screen (96 dpi) ... gives me a pixel pen. On a PDF printer (600 dpi), it gives me a pen that is much thicker than half an inch.

What am I doing wrong? What is the correct way to create a non-scalable pen in GDI?

Answer 1

Pen Transform. - Transform . , .

gdi +, < 1,5, .

: http://www.bobpowell.net/scalepens.htm

( PageUnit , .. Dunno, )