Random small polygons appearing during polygon offset

[Eswcvlad]

Hello,

I've managed to find another strange issue during my testing. See the image below. Black line is the original polygon. Green is the polygon with a positive offset and red is the polygon with a negative offset.

You can see that there are some random, like 3 or 4 point, polygons from the offsets. Some of them are really bizarre, like one from the negative offset lies outside the original polygon:

Here is the C++ code I've used for testing: test.txt

I've also tested on an older d3fbd4a commit and it doesn't seem to have this issue there, so this seems to be related to a relatively recent change.

[AngusJohnson]

Hi Vlad.

Here's the fix ...

In ClipperOffset::OffsetPoint() in clipper.offset.cpp (~line 319):

	if (AlmostZero(cos_a - 1, 0.01)) // almost straight
	{
		group.path.push_back(GetPerpendic(path[j], norms[k], group_delta_));
		group.path.push_back(GetPerpendic(path[j], norms[j], group_delta_)); //ADD THIS 
	}