Eliminate redundant transformations in area calculation #437
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When calculating an area with a transformation, we only really have to transform each point exactly once. However, the previous implementation was naively calculating each transformation twice. For simple transformations, this may not matter much. However, the transformation is user-supplied, so could be arbitrarily expensive to compute. The bounds of the for loop in the shoelace formula implementation have been reduced by 1 from from `[0, n)` to `[0, n-1)`. This is because the shoelace formula applies to rings, and the start and end points of rings are always the same. So the final iteration in the previous implementation was redundant.
albertteoh
approved these changes
Dec 2, 2021
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| // Each of the 4 points making up the polygon get transformed once each. | ||
| expectIntEq(t, count, 4) |
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I've probably misunderstood something, but in my mind, would have expected count to be 3 since the POLYGON is a triangle (3 vertices) made up of 4 points and we're looping 4-1=3 times?
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You're on the right track, but I think you may have missed that nthPt is called once before the loop starts. So yes, we do loop n-1 times, but we do 1 transformation outside the loop as well.
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Ah yes, the pt1 := nthPt(0). Thanks for clarifying!
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LGTM, and I'm sure I'm wrong (re: my comment), but just wanted to clarify why my understanding is wrong. :) |
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Thanks for the review! |
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Description
Check List
Have you:
Added unit tests? Yes, a new unit test to check the number of invocations. Existing unit tests ensure that the result of the area calculation is still correct.
Add cmprefimpl tests? (if appropriate?) N/A
Updated release notes? (if appropriate?) Yes.
Related Issue
Benchmark Results
N/A