Compound issue with line objects

[MazKaye]

I have created a number of lines using the pen tool in line mode and wish to group them together using the compound option (holding down Alt and pressing on Add from the toolbar). When I do so, the lines completely disappear. This does not happen when I try to group shapes together, in this case it works fine. What am I doing wrong?

[MEB]

Hi MazKaye,

Welcome to Affinity Forums :)

The boolean (geometric) operations don't work with lines, only with closed shapes (paths). So the only way to create a compound object from lines is if you convert them to shapes first going to menu Layer ▸ Expand Stroke (which may not be desirable in certain situations - you are not able to edit line width as a line for example).

[MazKaye]

Hi MEB,

 

thank you for your reply. I will try what you suggest and see if in my case it will work without indesirable effects.

 

Maz

[R C-R]

Hi MazKaye & welcome to the forums!

 

From what I can tell, in Affinity the booleans work on the areas enclosed by the paths. So lines don't actually have to be closed, but they do have to have at least three nodes that are not all in a straight line. So for example, you could use an open v-shaped line with 3 nodes or a [ shaped one. Basically, if you could apply a fill to the line & see it, even if you had to zoom in to extreme magnification, any shape or line will work. 

 

When the boolean is applied, any open paths in the result will be closed. The stroke width may change, becoming larger than the stoke width any of the included objects, sometimes considerably. This seems to be a bug because (for example) even if you use objects with exactly the same stroke widths, the result will be an increased width.

 

Expand Stoke also has some issues in that it can create a lot of extra nodes. If you are using it as MEB suggests, it is a good idea to change the Cap type to Butt or Square before applying the Boolean -- if you leave it set to the default Round cap type, it will create multiple nodes at the ends of the lines to follow the rounded end profile, making cleaning up the shape more tedious than it needs to be.

[Alfred]

From what I can tell, in Affinity the booleans work on the areas enclosed by the paths. So lines don't actually have to be closed, but they do have to have at least three nodes that are not all in a straight line.

 

Not quite: they can have just two nodes that are connected by a curved line segment. ;)

[R C-R]

Not quite: they can have just two nodes that are connected by a curved line segment. ;)

But then they would be curves, not lines (at least if you go by the Pen tool "line mode" definition of a line). B)

[Alfred]

But then they would be curves, not lines (at least if you go by the Pen tool "line mode" definition of a line). B)

 

Going by the Pen Tool mode definitions, your "line" would be a polygon! :P

[MEB]

R C-R,

Affinity does consider the enclosed "fill" area of a line as "closed" when performing a boolean operation but this is not the same as performing boolean operations between lines/shapes. It's simply connects the start and end points of the line (closing it) to be able to determine the result of the boolean operation. It just a technicality that's irrelevant in daily use because nobody will draw arbitrary lines guessing what the result would be. A user performs boolean operations because he knows exactly the resulting shape he needs/wants from the boolean operation to be able to move on with the project. Other programs do perform boolean operations between lines and shapes considering the area/width of the lines which is what users usually refer when discussing this subject - not the enclosed fill area generated by the line. So what's the point of bringing these technicalities here? Are you actually using this to produce anything other than creative edge cases?

[R C-R]

Going by the Pen Tool mode definitions, your "line" would be a polygon! :P

Well then, don't go by that!  :lol:

 

(Kinda) seriously though, a polygon is usually defined as a closed shape. See for example the Math is Fun "Is it a polygon?" examples. According to the same site (among others), a line is 1 dimensional & has no ends, while a line segment does, so technically "line mode" should be "line segment mode" & "polygon mode" should be something like "polyline mode."

[R C-R]

So what's the point of bringing these technicalities here? Are you actually using this to produce anything other than creative edge cases?

The point is to help new users understand how the booleans work in the Affinity apps vs. other apps they might be more familiar with, to reduce confusion & surprises & the time wasted because of that.

 

Consider for example the different results one can get when applying a boolean to a rectangle & a line with three nodes when the line's center node is offset by even a tiny fraction of a pixel vs when all three of the line's nodes are collinear. In particular, compare subtract, divide, & combine. (The latter is a good example of the stroke thickness bug.)

 

Also please consider the behavior when combined with the Expand stroke bugs, when trying to fill in areas defined only by lines, or with imported vectors, for example from an auto-traced raster image or an svg.

 

When I first started using AD, I wasted a lot of time trying to figure out why lines would disappear, why stroke widths would change (often so much that the result was unrecognizable), how to get the desired results that required the least effort & editing, etc. I just wanted to spare others from having to go through the same thing.