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Wouldn't the exception be for lines whose slope is irrational? (i.e. that can't be represented by a ratio of integers), so the repeating pattern is analogous to the repeating pattern in a decimal representation of a rational number.


How does a computer distinguish an irrational number from a good, (necessarily rational) floating-point approximation of one?


The algorithm only works with points with integer coordinates, so the slope is always rational.


I think you have the last words because line drawing algorithms become irrelevant if you use a Floating Point Unit.

just:

{ x++ and y+=slope } or { y++ and x+= 1./slope }

Then slopes are always rational in line drawing algorithms.


If y and slope are floating point in the first block then might not y end at other than the desired endpoint because of accumulative error?




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