Simple subtract operation throws open path error message

[iconexperience]

While working on path offsetting I found that very simple subtract operations on CompoundPath objects result in an open path error message:

// compound path
var cp = new CompoundPath();
var p1 = new Path.Rectangle(100, 100, 100, 100);
cp.addChild(p1);
cp.strokeColor = "green";
// path
var p2 = new Path.Circle(180, 180, 50);
p2.strokeColor = "red";
// subtract
var c = cp.subtract(p2);

The message is Boolean operation resulted in open path segments = 2 length = 65.8395631458437

The problem does not occur if p2 is subtracted directly from p1 (var c = p1.subtract(p2)).

Note that I cannot test against the develop branch at the moment, but the bug occurs in 0.9.25. If this is fixed in the new branch already please just close this issue.

[iconexperience]

This is really strange. At the beginning of computeBoolean() we reduce both paths, so cp is replaced by a simple Path, which should be identical to p1. But obviously something is different.

[iconexperience]

I found out that when we use the CompoundPathas path1 in computeBoolean(), its reduced clone _path1 unexpectedly has a parent (which is the 'CompoundPath). This happens, becausereduce()is called afterclone(), andreduce()` does not remove the resulting path if the original compound path has no parent. Here is a Sketch that illustrates this behaviour.

Maybe in CompoundPath.reduce() Item.reduce() the line

path.insertAbove(this);

should be changed to

this.parent ? path.insertAbove(this) : path.remove();
if (this.parent) child.insertAbove(this); else child.remove();

[iconexperience]

As an alternative I thought about changing the behaviour of insertAbove(), but I think the current behaviour is correct: If there is no parent, insertAbove() should fail and null should be returned.

So here is my summary:

• If reduce() is called on an item, the resulting item should have the same parent as the original item. This implies that if the original item has no parent, the result should have no parent, too.
• Currently if the original item has no parent, the resulting item can have a parent, because insertAbove() does nothing if there is no parent, so the child that will replace the original item will keep its parent.
• Since the behaviour of insertAbove() is correct, the reduce() function has to make sure that the parent is set to null if the original item has no parent.

CompoundPath.reduce() does not need to be changed, because if the CompoundPath is replaced by an empty Path, the new Pathobject initially has no parent.

Only Item.reduce() needs to be changed. I will create a pull request.

[lehni]

Well spotted! Shall merge this in now.