When I think of digital signal processing I think of things like audio and Fourier transforms. In my experience there’s quite a bit to graphics programming that’s different from that. A lot of shader code is linear algebra / matrix math, and physics equations for light. There’s also a lot of thinking about memory layouts and how to reuse calculations as much as possible.

I say this as someone who does a lot of graphics programming in my job but failed “Feedback Control Systems” the first time through.