Icelandian Startrails

This little badge design is based on something i saw on one of Björk's 'Debut' era (ca. 1993) releases.
I guess it was supposed to be Björk's logo: the letter B in a cool foreign looking alphabet/techno design, with the repeating gradient background in earthy browntones and a startrail on top.

Especially the startrail seemed like a nice idea for another brush dynamics tutorial, so i began exploring.

It went all well until i tried to add a stroke to the stars, which just didnt look good because small selections converted by Gimp into a path, do not result in very accurate paths. Especially the smaller stars looked more like little blobs with all sharp points gone.

So i switched to Inkscape and tried to recreate the startrail effect only to discover that its a lot harder than expected and gave up after banging my head against a wall for hours.

Last week i gave it another try and this time i got it working.

Not only was i able to delve deeper into designs with gradients, i also figured out how to make a vector startrail.

So after the jump i present to you, two techniques of making a startrail.
First in Gimp and then in Inkscape.


Lets start with Gimp:
Convert a circular selection into a path, then delete all the nodes and segments you dont need.
Its probably a good idea to do this on a duplicate, so you have a full circle backup for the decoration phase later.

A starbrush can easily be made with Gimp's parametric brush feature.

The great thing about the parametric brush editor is: its vector based.

In the brushes panel, click the little button at the bottom that says 'Create New Brush'.

The Brush Editor pops open.

Give it a name, choose the Diamond shape at a size of, say, a 100, crank up the 'Hardness' to 99 so it has a tiny amount of Blur (which is better for scaling), set the Spikes to 5 and the Angle to 17°, so its upright. For the Aspect Ratio i used 2,5 (matter of taste) and a standard Spacing of 100.

For the first teststroke, go to the Paths Tab, make sure the arc is highlighted and click on the Stroke Path button at the bottom of the tab. In the menu we want the 'Stroke with a paint tool' option, plus the 'emulate brush dynamics' checkbox ticked.

Adjust the Brushsize (i used 52px) and the Spacing.
At Spacing 100 there will be no gaps between the bounding boxes of each star, so lets try 135 which means 35% of the star's size will be used as space between brushstrokes.
This is the result:

Now how do we make the stars smaller with each brushstroke ?
This is where the Size brush dynamic comes into play ! What we need is the 'Fade' option.
Fade sets the distance in pixels over which the Brush Strokes are applied.

But how do we figure out the length of our arc ?
Install ofn-path-edits plug-in !

This plug-in has many uses, what we are interested in right now is the path-summary (for a full explanation check the documentary).
The path length is displayed in the middle of the plug-in message.

Create a new brush dynamic or use the 'All Purpose' as shown in the Bokeh tutorial .

Because we dont want any tiny stars, i limit the Size curve to approx 35% (remember one square represents 12,5%).

In the Paintbrush Tool Options, set the 'Fade length' to the value we got from the Path summary Message.

Make a teststroke, undo and then decrease the Fade until the biggest star lines up nicely with the start of the path. In this case its half the brushsize (676 minus 52/2 = 650).

If you want the same effect but inverted, reverse the Stroke direction with the Path Edits plug-in.
(another option is to invert the Brush Dynamics curve)

For a slightly less linear fade, which might look more pleasing to the eye, add a little bit of curvature to the Brush Dynamics curve. This gives the fading a tendency of more "volume".

That concludes part one of the tutorial.
As you can see this effect is all about finding the right balance of Size, Spacing and Fade values.
It can take a lot of teststrokes and hitting the Undo button to get it right.

Now for a similar effect in Inkscape.

Unfortunately making a startrail in Inkscape is not a live effect. The biggest advantage is that you will get better quality and easier editing. Im using Inkscape Version 0.92.5.

Make a star, convert to a path, duplicate and scale down to taste with the aspect ratio locked.

For the sake of the tutorial, i gave the smaller star a different colour.

Make a circle, flip it horizontally to change the direction and turn it into an arc.
Do NOT convert into a path !

Select both stars and call up the Interpolation Extension

(Extensions → Generate From Path →  Interpolate)

If you want a gradient of colours, check the 'Interpolate Style' checkbox.

Ungroup the interpolated stars, then select them all and call up the Restack Extension

(Extensions → Arrange → Restack)

For the effect to work its crucial that all stars have the correct z-order.
(the biggest star must be at the bottom and the smaller ones on top of the z-order, in ascending order)

Finally call up the Arrange dialogue (Objects → Arrange).

Go to the Polar Coordinates tab, rubberband-select all stars and the arc and apply the effect with the settings i used below.

Although i used the same size for stars and arc, the effect looks a bit different compared to Gimp.
You might want to interpolate less stars so it doesnt look so crowded.

Get rid of the arc by either removing the stroke colour or hide it behind the background.

In case you forgot to flip the arc, this will happen :
(which threw me off big time when i tried to figure out how to do the effect, lol)