An alternative is a lexicographic sort where

x[i]>x[i-1] or y[i]>=y[i-1]  for all i>0

You may find a lexicographic sort in the library BOSL2:

https://github.com/revarbat/BOSL2/wiki/arrays.scad#sort

Em qua., 30 de dez. de 2020 às 07:08, TLC123 torleif.ceder@gmail.com
escreveu:

On Wed, Dec 30, 2020 at 3:09 PM Ronaldo Persiano rcmpersiano@gmail.com wrote:

Thanks a lot Ronaldo, that sounds really good for my use case.

Bruno

TLC123 wrote

It only looks weird if you want to build something with a sorted list.
Could it be used as a function in preview to build a bounding box?

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If you want to make a bounding box from a list you need to treat the x and y
coordinates independently.  Mixing them together with addition isn't useful.

The idea of sorting by x+y is like sorting on the distance your points are
away from the line y=-x.  Could be useful for something, but note that
points on lines with slope -1 are all "equal, so [0,0] and [-1000,1000] are
"equal" and would hence have indeterminate order unless you impose a
secondary ordering.  This is analogous to sorting just on x and ignoring
y---you just rotate by 45 deg before doing the sort.

You could sort on distance from a point, e.g. norm([x,y]-p) for some point
p.  Then circles will be "equal".

Lexicographic sort (noted by Ronaldo) is how words are sorted in a
dictionary: you sort on the first vector component ("letter") that doesn't
match.  It doesn't make geometrical sense, but it puts an order on every
vector---two vectors are "equal" in this sorting only if they match at every
entry.

lar3ry wrote

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adrianv wrote

Right. Sorry, I should have mentioned that I was referring to TLC123's
"Sorting by x> or y>", with emphasis on the OR.

After I posted, I realized that since we don't  keep track of geometry in
preview, it means that the bounding boxes would have to be calculated from a
point on each object, and talking tinto account every translation,
extrusion, mirror, rotation, etc. Clearly not conducive to having it display
the preview sometime in the coming week.

But then I wondered... During a preview, it has to draw everything. How much
overhead would it cause to compare and keep the maximum values on each axis
as it is being drawn. I know this would have to take into account
difference(), but I don't know what else might be a problem.

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I think that "x> or y>" was a terse restatement of lexicographic sort,
meaning that you apply the compound condition, not one condition or the
other one.

I'm not sure what you want the bounding box of.  If you have a point set you
can get its bounding box.  If you're doing operations to the point set that
give you a new point set you would calculate the bounding box from the final
results.  Note that it is possible to compute a bounding box geometrically.
(BOSL2 has a module that does this.)  I'm not sure how fast it is, though.

lar3ry wrote

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