(08-12-2025, 01:47 PM)Scallact Wrote: This apparently trivial feature actually hid a rabbit hole. The requirement of cutting a Bezier curve at a specific point send me through a deep dive into Bezier curves theory and algorithms. :-)

(08-12-2025, 09:24 PM)Ofnuts Wrote:

(08-12-2025, 01:47 PM)Scallact Wrote: This apparently trivial feature actually hid a rabbit hole. The requirement of cutting a Bezier curve at a specific point send me through a deep dive into Bezier curves theory and algorithms. :-)

Welcome to the club. Did you see Freya Holmer's videos on YT?

(08-12-2025, 10:55 PM)Scallact Wrote:

(08-12-2025, 09:24 PM)Ofnuts Wrote:

(08-12-2025, 01:47 PM)Scallact Wrote: This apparently trivial feature actually hid a rabbit hole. The requirement of cutting a Bezier curve at a specific point send me through a deep dive into Bezier curves theory and algorithms. :-)

Welcome to the club. Did you see Freya Holmer's videos on YT?

Now that you mention her, I think I saw that video some time ago, but I had no use for it at that time.

The most useful ressources I've found are this page and this algorithm. But I had a lot of tinkering to bring everything together, let alone a few imperfect tries with very home made algorithms.

On the upside, I learned a interesting new things.

(08-13-2025, 09:20 AM)Scallact Wrote: Do you suggest that we can find the exact t parameter of a specific point on the curve by solving a third degree equation? I found a paper about this, but it's unreadable to me given my level of math notation understanding.

(08-12-2025, 01:47 PM)Scallact Wrote: This is my proposal for a plugin dedicated to a much requested feature in GIMP 3.0: stroke paths with an arrowhead at the end.
It has one genuine feature, compared to other similar plugins (AFAIK): the body path is shortened to ensure that the arrow tip ends up reasonably well aligned with the path's last point.
This apparently trivial feature actually hid a rabbit hole. The requirement of cutting a Bezier curve at a specific point send me through a deep dive into Bezier curves theory and algorithms. :-)

The image below shows a selection of arrowheads styles available:



The documentation is here, and you can download the current version here.

Make sure you place the folder named "pl_stroke_arrows" in the GIMP plug-ins folder inside your profile.
Depending on your operating system, make the file "pl_stroke_arrows.py" inside this folder executable.
The plugin should appear at the bottom of the "Edit" menu.

The plugin has been tested, but some new bugs will probably happen. Please report here, preferably with a downloadable .xcf file to exemplify the case.

(08-13-2025, 11:33 AM)denzjos Wrote: I tested the plugin on different paths with different parameters and I found no errors. Thanks

(08-13-2025, 09:20 AM)Scallact Wrote: Do you suggest that we can find the exact t parameter of a specific point on the curve by solving a third degree equation? I found a paper about this, but it's unreadable to me given my level of math notation understanding.

Quote:Yes, this is what I did for ofn-path-bend (in fact this is why ofn-path-bend is so fast). Your problem of course is that you have one equation per  Bézier segment, so you are not looking just for t but for t in the adequate segment. However, 1) you can often guess which segment, and 2) in most case for the other segments you won't get a solution for t in [0,1] and when you have one you can check that the solution for ŧ works for bother x and y (and unless you path does a loop there will be only one such pair in it).

(08-13-2025, 01:46 PM)teapot Wrote: Hi Scallact, Thank you for the plugin, it's working nicely here and I gave it some tricky paths to test. Well done for tackling splitting the path, it looks a tough call. I especially like that you have a keep-paths option.  One small observation, perhaps a message would be nice when the path cannot be handled as I was sometimes getting a new empty layer in the really tough cases.