How the loader draws the dot-based Saturn in Elite's epic loading screen
This deep dive is a work in progress. It covers the drawing of Saturn in the PLL1 routine in the loader.
Part 1 (PLL1) x 1280 - planet
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Draw pixels at (x, y) where:
r1 = random number from 0 to 255
r2 = random number from 0 to 255
(r1^2 + r2^2) < 128^2
y = r2, squished into 64 to 191 by negation
x = SQRT(128^2 - (r1^2 + r2^2)) / 2
Part 2 (PLL2) x 477 - stars
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Draw pixels at (x, y) where:
x = random number from 0 to 255
y = random number from 0 to 255
(x^2 + y^2) div 256 > 17
Part 3 (PLL3) x 1280 - rings
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Draw pixels at (x, y) where:
r5 = random number from 0 to 255
r6 = random number from 0 to 255
r7 = r5, squashed into -32 to 31
32 <= ((r6 + r7)^2 + r5^2 + r6^2) / 256 < 80
Either this is true:
((r6 + r7)^2 + r6^2) / 256 >= 16
or both these are true:
((r6 + r7)^2 + r6^2) / 256 < 16
r5 >= 128
x = r5 + r7
y = r5