By the way… there are many shade styles available in orx/orx-shade-styles at master · openrndr/orx · GitHub so you don’t need to write shaders yourself (many of them only available when using version 0.4.5).
I opened this issue to be able to apply those same shade styles to strokes, not only fills.
Meanwhile I just figured out a little hack:
val img = loadImage("data/images/cheeta.jpg")
val ss = imageFill { image = img }
ss.fragmentTransform = ss.fragmentTransform?.replace("x_fill", "x_stroke")
Here I load an image and use the new imageFill shade style which works for fills only. But then in the next line I replace any mentions of x_fill to x_stroke and voilá! Now the style applies to lines instead 