GIMP Script: Tapered Stroke on a Path

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< Golden Objects in Gimp | GIMP Script: Sample a Gradient along a Path >

Monday, September 29. 2008

Several times I have seen techniques in PhotoShop that use brush dynamics to taper a stroke. Unfortunately GIMP doesn't have this capability (yet...but it is rumoured for 2.6) so I wrote a little script-fu to do it!

A warning up front... it ain't too fast, but it works. Using the script is straight forward.

Draw a path using the pen tool, then switch back to the paintbrush tool. You need to select the paintbrush tool as the script strokes with the active tool, so you could even, for example, "erase" tapered strokes. The script registers under the Edit menu as "Tapered Stroke Path..."

Calling the Script

The dialog allows you to select the start width, end width, spacing (20 percent is a good default, but by setting it to 100 you get a string of pearls effect), and a parameter called "Taper Exponent". This control the rate of taper. At 1, the taper is linear from the start to the end. At values less than 1 the taper changes faster, and greater than 1 the taper changes slower (nearer the end). The default is 5, which seems good for drawing rivers on a map (what I designed it for).

Options

Here is the result after stoking in black with the defaults. I have turned on the path visibility to show how it lines up:

A Tapered Stroke

Couple of things... It will only stroke the first segment of a multi (broken) segmented path. If there are no paths, the script will run but error out.

Download the script here. Hope people find this one useful!

-Rob A>

Posted by Rob A in Gimp at 20:50 | Comments (6) | Trackback (1)

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GIMP Script: Sample a Gradient along a Path
Previously, I had developed a small script to take an image and turn it into a GIMP gradient. This was mainly due to my desire to convert some of these tonal gradients into actual GIMP gradients. This script was posted to the gimp-plugin[?] repository b

Weblog: Rob A's (Im)personal Blog
Tracked: Oct 08, 10:22

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Doesn't seem to work right in 2.6, just stays on one brush.
Hope you can fix this as 2.6 still can do this.

#1 Newt (Link) on 2008-10-05 02:45 (Reply)

Newt-

I don't think it is necessary in 2.6 as brush dynamics can be simulated along path strokes!

-Rob A>

#1.1 Rob A (Link) on 2008-10-05 09:55 (Reply)

Yes, the dynamics can be used, but it's nowhere as good as your script.
Here's why:
1. You can select what path from the script.
2.You can choose exactly what size to start and end with.
3. You can choose from the script the spacing of the brush.
Most important is number 2 as the dynamics scale is based on the length of the path, so if you start with x size you have to end with z size, in other words the end size is always based on the beginning size.
If only your script could use different brushes it would provide something wonderful.

#1.1.1 Newt (Link) on 2008-10-05 12:34 (Reply)

OK- I understand now. GIMP only exposes dynamic scaling for programmatic brushes, i.e. the same ones you create with the New Brush command. It can't scale other brushes (gbr) created from bitmaps. I could modify the script to allow you to pick a programmatic brush... that would give a bit more flexibility... Would that suffice?

-Rob A>

#1.1.1.1 Rob A (Link) on 2008-10-06 07:59 (Reply)

Yes, here's an example of what Im talking about.
http://i24.photobucket.com/albums/c2/mrenewt/devilinside.png
The horns are from a custom brush.
Ordinarily you would have to make a new layer for each stroke, and then resize it. As you can imagine that would take quite some time.

#1.1.1.1.1 Newt (Link) on 2008-10-06 11:33 (Reply)

Here is a sample made using the 2.6 stoke along path with brush dynamics... I think it provides a similar result as your sample.

http://www.silent9.com/blog/uploads/gimp/test.png

I did check, and as of 2.6 they have still not exposed brush scaling in the pdb, so we can't change brush size using script-fu.

-Rob A>

#1.1.1.1.1.1 Rob A on 2008-10-06 13:30 (Reply)

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