No, I'm afraid not. From the documentation: The dash pattern is specified in units of the pens width; e.g. a dash of length 5 in width 10 is 50 pixels long.

And fractional line width units simply don't work. I tried that.

Frankly I am surprised that the developers did this. I can see line width units for dashes and spaces as a convenience, but not at the expense of not being able to specify them in pixels.

Unless I can find a way to use a Cairo context in Qt, I am afraid I am not going to be able to use Qt. So far, despite searching, I have found no information on that possibility.

Sorry for the delay in getting back.

The example is a single 130 pixel wide spaced line drawn using the Cairo graphics library, where cr is a cairo context. This works with any Cairo line, not just straight lines.

I was hoping that Qt had a similar capabilty.

 double dashes[2] = {7.5, 30.0};
 cairo_set_source_rgba(cr, 1.0, 0.0, 0.0, 0.5);     
 cairo_set_line_width(cr, 130);                      
 cairo_set_antialias(cr,  CAIRO_ANTIALIAS_FAST);
 cairo_set_dash(cr, dashes, 2, 5);
 cairo_move_to(cr, 200, 200);
 cairo_line_to(cr, 1000, 200);

It' just QPainter and QPen in a QPaintEvent on a simple MainWindow. I did this as a test. I have very little Qt experience so I wanted to see if what I want to do is even possible.

You should explain what you are using to draw these lines and on what you are drawing them.