Can I create an .fsh file from an image?

I wanted to use a png image to create a pattern for an SKSpriteNode. Supposedly:

Pattern images are not supported via UIColor in SpriteKit

So I am supposed to use an .fsh file for shading. The thing is, can I create such a file from an image? Everywhere I've looked only show's mathematical methods for creating those files.

I hope this is something that is possible