Hello All,
I've had this problem for a while now.
I can have an original item. Let's say just a box made with rectangle tool.
Give it a thick outline (let's say 4.0) and then click "Object-Convert outline to Object".
I will then copy and paste the second image, then flip it horizontally and move it to overlap original image.
I then click the second image, hold shift and click first image to select them both.
When I click "WELD" they will weld but the first image turns completely black.
If I click the first image first, then "SHIFT" and the second image, the second image turns black.
What my goal is, is to have an object like this but welded.
I have tried "TRIM" "INERSECT" "SIMPLIFY" "FRONT MINUS BACK""BACK MINUS FRONT" "COMBINE"
Now what I'm working on is more detailed than this, but this is an explanation. I understand that by just moving the second object to overlap the first object without flipping it will weld. It only happens when I have an item that is flipped either horizontally or vertically.
The paths get inverted when you flip. You can see that after the weld does , the inner shape is still there, despite being filled with black. Go into node edit mode, select the inner subpaths and reverse direction. You will be good.
There are two ways to determine how subcurves should be displayed, the Even-odd and Nonzero (winding) rules.Even-odd is the "normal" fill rule in Draw (except for text) but for some reason it will change to nonzero when you convert an outline to curve, and when you then flip the copy, the curves go in the "wrong" direction and will look solid when you weld the objects together.Suku described how to correct them (enabling "Show curve direction when editing" in Options > Nodes and Handles, makes it easier to see the direction).There is also another way to "fix" this problem: Disable "Fill winding" (change to Even-odd rule) in the Properties docker, Fill tab.This will make it look correct but the curves are still running in the wrong direction, and this may (or may not) cause problems along the way. It normally doesn't matter what rule is used or in what direction curves run, but it is always good to know about them and how to fix potential problems.