Weird distortion with Fill when vectors are grouped

I would like to report an issue I have encountered yesterday - the closest topic I could find related to the matter is this one but the behaviour occurs from a different reason: Fill rectangles distorted in preview and job

Same shapes get a weird distortion when they are grouped. See attached images from the preview, the actual engraving also contains the distortion when grouped…
The distortion does not become visible on any of wireframe or filled views.

Layer is set to fill at 0.1 line interval. Shape coordinates and layer settings are identical - so there’s no change with the object properties except being grouped and ungrouped.

Lightburn 0.9.16 - 64 bit - Windows 10
60x40 chinese with AWC708s

grouping bug.lbrn (103.6 KB)

Thank you for reporting this. Please post the file so we can have a look.

attached to the original post now.

Thank you for updating. When I look at this file, I notice that the grouped objects that display this “weird distortion” are angled slightly and not parrell to your scan angle. This is why you are seeing a “shifting” in that fill.

Thanks for your answer.
Yes, that was the first thing I looked at too - a slight angle
It doesn’t quite answer for me why the output is different when the same shapes with that slight angle are grouped or ungrouped

So; does Lightburn override this angle of shapes to zero when the objects are ungrouped (or changes the scan angle automatically & independently for this shape) and that’s why I get a nicer output, compared to the grouped version of the exact same slightly angled shape? Somehow I didn’t want to give this a chance and wanted to report it.

Thank you for the additional follow-up, this has been helpful for me to find what you are talking about.

I can reproduce this behavior. If I simply ungroup those shapes, I can get them to cut as you’d expect.


This part of the E is angled:

It’s very hard to see with the smoothed rendering, but easy to see if you use coarse rendering, as shown above.

When you group things, because you have “fill groups together”, the software is merging everything in the group to figure out where the fill should start and end, and where to place the lines for the fill.

With everything grouped, the set of lines for the fill start up here:

… and are placed every 0.1mm from there to the bottom of your design. If you don’t group, then each shape is treated independently, so the scanned lines will end up placed differently.

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