Designer: Convert a straight line segment into a curved one

[max1josef]

Is there a simple way to convert a straight line segment into a curved one with smooth nodes, without affecting the neighbour segments? See the screenshot for clarification. In Inkscape I would click on segment BC with the node tool and choose "Make selected segments curves" and then "Make selected nodes smooth".

[Old Bruce]

I would just switch to the Node Tool and drag the BC segment out to a curve.

 

[max1josef]

3 hours ago, Old Bruce said:

I would just switch to the Node Tool and drag the BC segment out to a curve.

But you still have no smooth nodes. You have to adjust the control points, which sometimes even snap to give smooth nodes, sometimes not.

[Pšenda]

17 hours ago, max1josef said:

convert a straight line segment into a curved one with smooth nodes, without affecting the neighbour segments?

Automatic no.

Node Tool, select BC node, Context toolbar - Convert to Smooth.
Select B node, Click + Alt to left handle.
Select C node, Click + Alt to right handle.
Adjust the resulting arc shape as needed (snap the handles parallel to the appropriate line segment).

Edit: I don't know the benefit of BC nodes being Smooth, but I've noticed that when cusp is created it changes node to Sharp.
Then, after converting the BC nodes to Smooth, it is possible to move the left/right handle of the B/C node to the A/C node (use snapping), and then adjust the arc again (use Drag+Shift).

[JimmyJack]

I think this is actually a bug. Smooth should be smooth and Smart should be smart.
We should be able to just select the two nodes and choose one or the other. But we are getting a Smart result for both options.

At any rate, I'd:
• Delete the middle section.
• select the end nodes and make them Smooth
• join curves

(to see what I mean about a bug, after deleting the middle segment assign the two nodes instead to be Smart, and join.)

[lacerto]

(...)

[thatGuy]

you can use construction snapping to restore the linear segments after node type conversion without splitting/re-joining the curve

[GarryP]

In addition to the advice above, if you are not too bothered about the node positions, you can use the Corner Tool to get something done quickly.
See my attached video where the thick black curve shows the original and the thinner red curve is a copy being manipulated.
As you can see, the modified curve doesn’t fit to the original nodes but this might not be important if you just want something quick.

[R C-R]

16 hours ago, max1josef said:

Is there a simple way to convert a straight line segment into a curved one with smooth nodes, without affecting the neighbour segments?

As @thatGuy mentioned, by using construction snapping this can be done in 3 steps. That also can be used to demonstrate that many different curve segments that do not affect neighboring ones are possible. For example, in this 2 smooth curves.afdesign file, both the green "smooth 1" curve & the red "smooth 2" one include a smooth segment that does not affect neighboring ones. If you hold down the Shift key, you can drag any of their node handles to a wide range of locations to create a different curve segment that still does not affect neighboring ones.

IOW, there is no one unique segment shape that does this, so any automatic method for doing this would have to pick one, which may or may not be the shape you want.

[Pšenda]

6 hours ago, Lagarto said:

b) But this happens (the location of node C is moved):

It looks like a bug.
If the CD segment rotates (Reverse curve), Convert to Smooth works correctly on both nodes (just like on the AB segment).
However, if the segment rotates once more - and point C returns to its original position, it makes a bugagain.
P.S. but even point D behaves differently - in the original and rotated/reverse position.

[max1josef]

Thank you all for your suggestions. I will go for the construction snapping method.

5 hours ago, R C-R said:

IOW, there is no one unique segment shape that does this, so any automatic method for doing this would have to pick one, which may or may not be the shape you want.

This is where smooth nodes (as they work in Inkscape) come in handy: when you drag the curve after conversion (the curve itself, no need to drag the control points) after conversion, the nodes remain smooth (they are restrained to be staying smooth).

BTW: What screen recording software are you using? I'd like to post videos like you did, too.

 

 

[R C-R]

1 minute ago, max1josef said:

This is where smooth nodes (as they work in Inkscape) come in handy: when you drag the curve after conversion (the curve itself, no need to drag the control points) after conversion, the nodes remain smooth (they are restrained to be staying smooth).

Yes, they are smooth but they are converted to just one of many possible curvatures. What if you want a different one that is more or less rounded or is less symmetric?

[max1josef]

As I wrote above: after automatic conversion I can drag the curve (with Inkscapes node tool) wherever I want to, with the nodes staying smooth. This is something I really miss in Affinity designer.

[Pšenda]

7 minutes ago, max1josef said:

with the nodes staying smooth

I don't know how Inkscape displays different types of nodes, but yours don't look like Smooth - they don't have a two-way handle.

 

[max1josef]

They show only one handle, because the first and last segments are straight lines - so there is no need for handles.

[R C-R]

46 minutes ago, max1josef said:

As I wrote above: after automatic conversion I can drag the curve (with Inkscapes node tool) wherever I want to, with the nodes staying smooth.

After you use construction snapping (I think just one more step than with Inkscape is it not?) you can do the same thing in Affinity by using the Shift key to constrain a dragged handle to any point that does not affect the neighboring segments.

You could also do the same thing by deleting the two handles that extend into the segments you want to remain unaffected & then dragging the segment around instead of its nodes.

It is maybe a bit less convenient but not overly so.

[lacerto]

(...)

[max1josef]

44 minutes ago, R C-R said:

After you use construction snapping (I think just one more step than with Inkscape is it not?) you can do the same thing in Affinity by using the Shift key to constrain a dragged handle to any point that does not affect the neighboring segments.

Thank you for adding the essential tip (holding the Shift-Key). Now I have a really practical workflow for my task.

47 minutes ago, R C-R said:

You could also do the same thing by deleting the two handles that extend into the segments you want to remain unaffected & then dragging the segment around instead of its nodes.

I also tried this, but the nodes don't remain smooth when I do this.

48 minutes ago, R C-R said:

It is maybe a bit less convenient but not overly so.

Agreed! I'm happy with your solution!

[R C-R]

3 hours ago, max1josef said:

I also tried this, but the nodes don't remain smooth when I do this.

True, but it is just another way of making it possible to change the curvature of the curved segment without affecting the neighboring ones.

In a round about way the point (no puns intended) I am trying make with all of this is in Affinity there are actually 3 kinds of "sharp" nodes: those with zero, one, or two control handles. The context toolbar "Convert" button only offers conversion to the first kind. Perhaps it would be better if it had all 3?

[Pšenda]

3 hours ago, max1josef said:

Thank you for adding the essential tip (holding the Shift-Key). Now I have a really practical workflow for my task.

22 hours ago, Pšenda said:

and then adjust the arc again (use Drag+Shift).

See Status bar.

 

5 hours ago, max1josef said:

They show only one handle, because the first and last segments are straight lines - so there is no need for handles.

But then node B and C are not Smooth (as you require), but are Sharp.
Affinity works exactly the same (see my earlier description).

[JimmyJack]

14 hours ago, thatGuy said:

you can use construction snapping to restore the linear segments after node type conversion without splitting/re-joining the curve

Nice! It does however yield a different result 😉.

 

6 hours ago, max1josef said:

As I wrote above: after automatic conversion I can drag the curve (with Inkscapes node tool) wherever I want to, with the nodes staying smooth. This is something I really miss in Affinity designer.

Yes, we should have this option.
We already can grab and manipulate the individual segments we just need a modifier implemented to constrain the handles to be straight (I'm not talking about adjusting them one at a time). We can constrain bez handles in other situations so I don't think this is a hard ask .... or to do!

[Pšenda]

5 minutes ago, JimmyJack said:

to constrain the handles to be straight

Node Tool, Context Toolbar - set Perform construction snapping (last Snap option). Handle and Node has purple colour.

[JimmyJack]

8 minutes ago, Pšenda said:

Node Tool, Context Toolbar - set Perform construction snapping (last Snap option). Handle and Node has purple colour.

LOL, yes, as you can see that is what I used in my GIF. (edit: oh the GIF never uploaded.... I'm getting a -200 error? Video below instead... May bad)
It's not what my comment is about which is constraining both adjacent handles at the same time when manipulation the curve segment itself. As in @max1josef's example. 👍

[Pšenda]

5 minutes ago, JimmyJack said:

yes, as you can see that is what I used in my GIF

Yes, but you use it in another situation - to attach one handle of the Smooth node.
Because I responded to "to constrain the handles to be straight", I meant the straight movement of the handle at the Sharp node, as seen in the picture from the OP.

[JimmyJack]

7 minutes ago, Pšenda said:

Yes, but you use it in another situation - to attach one handle of the Smooth node.
Because I responded to "to constrain the handles to be straight", I meant the straight movement of the handle at the Sharp node, as seen in the picture from the OP.

The OP was never moving individual nodes (that's what he ended up doing in the end as a workaround). You can see his Inkscape cursor is on the curve itself, not on the node. 
And yes we can constrain handles in different ways one at a time (that's why I said "We can constrain bez handles in other situations").
Which is why this ability doesn't seem like such a hard behavior to add.