Exercise 4.1 The following filters manage tilability:
Image: Filters > Distort > Ripple
Image: Filters > Render > Clouds > Solid Noise
Image: Filters > Render > Pattern > Maze
Image: Filters > Render > Pattern > Sinus
The filters in the Image: Filters > Render menu are especially useful for generating textures. See Chapter 17 for more details.
Exercise 4.2 Oilify was used the second time to soften the curve. If you skip it, edge detection generates an angular pattern. You could try using artistic filters other than Oilify and Cubism in GIMPressionist. For example, you could replace IWarp with another distort filter, such as Waves, to create a pattern with strong central symmetry that disappears if you then apply a filter like Cubism.