Speed of rotation

to make it rotating faster you can change incrementing
for instance

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for quicker - you are anyway dealing with floating point numbers - why not use

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and then correct for smaller values other places, like:

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etc.

By the way - there is no good reason to do this part:

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(or by 1800 in the above example)
inside the loop (twice - both for left and top).
Consider calculating it before the loop starts and storing in additional variable.