The textured torus was a much larger resolution wireframe, rendered to grayscale. I increased the contrast to make it almost completely white. Then I surrounded it with a 1-pixel contour of black, twice. You can see this contour if you collide your ship to turn the background white. (The background is actually white with alpha transparency, over a rectangle that gets changed from a black-to-black gradient to whiter colors when you get hit. )
I didn't use any shaders in this game. I'm still learning the code, and I was worried that writing everything to a surface, then writing the surface to the screen, would be yet another processing operation, and the game is already dropping frames! 😅
And thank you for your kind words. 😊 There's a lot of really good submissions, and it's great to see what people make! I am learning so much more about the danmaku genre.