How to create bars at sequential positions that mask another image?

Hi everyone,

I would basically like to create a binary stimuli of a bar that moves across the screen (I just need to make the frames of this) in eighteen steps. It moves left to right, then top to bottom, and top-left to bottom-right. It should move across a circular aperture, so basically we see the white circle in bar segments. It should be like the attached images, but I need to make the bar twice as wide. If anyone has any pointers that would be great! I can create the bar in consecutive positions left to right and top to bottom, but not sure about diagonally. I'm also not sure how to make it mask the circle, so the circle only shows through the bar.

Sorry if I'm not clear, any help would be great!

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