Posted by dxli on Dec 20, 2024; 1:02pm
URL: https://forum.librecad.org/Lines-pattern-scaling-tp5725741p5725844.html

Hi johnfound,

Just want to be confirm with you on a few items:

1. in rs_linetypepattern.cpp, it is stated the patterns are defined in pixels. I few we may have to redefine this one. Better to make LibreCAD patterns defined in physical distances, like mm/inches. By defining line patterns in display/rendering space allows zooming in/out, with roughly the same line pattern appearance;
2. Qt line patterns are defined in line widths, and line width is taken as 1 pixels, if defined to be 0;
3. If we define LibreCAD line patterns in mm,
    p_Qt = p_LC * dpmm/(lineWidth)

with p_Qt and p_LC as the pattern values for QPen and LibreCAD (rs_linetypepattern), dpmm as the standard dots per mm, and lineWidth the line width in pixels.

A few things need improvement:

1. the cap style effects on line patterns;
2. DPMM may not be reliable;
3. connected entities, like polylines and splines.

johnfound wrote

Well, it seems I have a working solution of the problem with the line scaling.

Here is the commit:

https://asm32.info/fossil/librecad/info/679836fcf52e840c

But some bugs and glitches are possible.

I have tested it on the display, print preview and pdf export and everything seems to be OK. But still there are too many combinations between the different line widths and line screen widths and this makes the code too complex.

Here is a dxf file, I used for the tests:

dashed-lines.dxf

The left "center line" and the right "fake center line" should always look equal if everything is OK.