GIMP’s new free‑poly tool

21 June 2008, 13:42

Recently there was a heartwarming post on the graphics planet:

‘Another exciting thing that will be in 2.6 (and the next 2.5 release) is the hybrid polygon/free select tool! It is truly a thing of beauty…’
David Gowers, featured on meetthegimp.org

The story of how the the free‐polygon tool came about is one of developer–interaction architect cooperation.

going poly…

The initiative came from Martin Nordholts. He had built a proof‐of‐concept polygon selection tool and was asking me to write UI specification for it. First I asked my self if GIMP really needed this tool. Is it not replicating what can be done with the path tool?

After I convinced myself that it was a good idea to have a polygon select tool, I had to deal with yet‐another‐tool in the GIMP toolbox. One of my goals is to end up with less tools than now, not more.

magic combination

So following my intuition I asked Martin on the irc: ‘is there any way that this polygon tool can be integrated with the rectangle selection tool?’ Martin answered along the lines of: no, but what about the free selection tool?

Brilliant. Not only did I instantly know this was a great idea, I also instantly knew what it was going to feel like to use this tool. Martin and other developers on the irc could not imagine how free and polygon segments could be represented on screen and created by users in an elegant way. I knew within minutes how this was going to work.

small is beautiful

Fuelled by enthusiasm, I wrote the initial UI specification in an hour and a half. It was really a straightforward merge of two simple tools: like before, clicking was going to create polygon segment, dragging free segments. My trick was to place a polygon point at both ends of each free segment, enabling the connection between both types of segment.

I was determined to keep it simple. Concise, straightforward tools like this fill me with more satisfaction than more complex ones—although necessarily so—like the rectangle selection tool (13 pages of specification). In a similar fashion I am more proud of the simple but super elegant applications I have designed for Nokia, e.g. the Translator, than of the complex ones, e.g. the email client.

tit for tat

The refinement of the tool after development commenced is a further example of our cooperation. Martin contributed the 15 degree constraints (using the control key) as seen on other tools and better modification of free segments—rotate and resize—when grabbing one of their handles.

I saw that these were indeed improvements in user interaction and integrated them in the UI spec. Martin relied on me for UI solutions for corner cases he encountered.

One was the issue of whether the polygon points should be always visible—quick to grab, but high visual noise—or only on mouse‐over—clean but slower. I kept in mind the activity of tracing existing images where you want the points to be invisible to inspect if the trace is correct to the last pixel and quick to grab, to adjust a point to the last pixel. I squared that circle by making points visible when the mouse is nearby and figuring out how far away nearby is.

Another issue was that polygon points are really in the way when you want to create another one close or on top of it. This also affects continuing with a free segment exactly from where the last segment ended. My solution: the shift key suppresses existing points, clearing the way to create new segments anywhere.

With all these UI changes, I guarded the conceptual integrity and ensured that we were not introducing bloat, getting in the way of the core value of this new tool.

closing credits

What we have seen here, I see in general in the projects I do. Developers drive innovation on a technology and feature level. Interaction architects create the UI that actually works. UI that is integrated in the overall concept and that supports the activities that users undertake.

In the middle is cooperation between us, where ideas are brainstormed, solutions are cooked up. And where each side determines if this is the right way forward. Developers for the technological aspects and interaction architects for the user interaction.

test drive

Go on, try out the new free‑poly tool of GIMP 2.5. We had a ball creating it for you. You will find it under the trusty lasso icon of the old free selection tool. That is, until we tackle the update of that…

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3 comments · post a comment

at 24 June, 2008 06:08,Blogger David commented
Elegant solutions are always so satisfying.
And it's always inspirational to read of moments of pure insight where you understand exactly just what must happen.

"You will find it under the trusty lasso icon of the old free selection tool. That is, until we tackle the update of that"
This is a bit ambiguous. To
clarify: The hybrid free/poly select tool has replaced the free-select tool. It's still called 'free select' and the icon is still the 'free-select' icon. In a future update those things will change.

Is that what you meant? 
at 24 June, 2008 14:49,Blogger peter sikking commented
yes, that is what I meant. certainly the icon needs an update. thanks for clarifying. 
at 26 October, 2009 03:35,Anonymous Jamie Macdougall commented
Nice tool... if you're using a mouse.
Closing the selection with a tablet by clicking on the first selection handle will invariable shift the whole selection.
I assume the developers use Wacoms or similar tablets, so I've surprised this slipped past. 

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