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Full Version: T-Junctions and Y-scaled flat primitives in the Library Spec
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T-Junctions:
These are discouraged in the file format spec:

Quote:Where possible, abutting polygons should share common verticies.

I'd like to explicitly disallow in the library spec.

Y-scaled flat primitives:
These are not mentioned in the file format spec or the library spec.
I'd like to explicitly disallow in the library spec.
(2022-05-04, 18:59)Orion Pobursky Wrote: [ -> ]T-Junctions:
These are discouraged in the file format spec:


I'd like to explicitly disallow in the library spec.

Y-scaled flat primitives:
These are not mentioned in the file format spec or the library spec.
I'd like to explicitly disallow in the library spec.

+1
T-junctions
Might be necessary where 2 holes are close to eachother and using ndis is the better choise than tang prims.
But today we have tang, ndis and tndis, so avoiding T-junc is easier.

Flat primitives
It is wrong to call them "Y-scaled". It would be better to talk about "flat prims scaled in three dimensions".
I should mention that in some cases, for example axle primitives, T-Junctions are something that comes along with the way those primitives are made and how those are usually encased in other primitives. If we are going to get rid of any T-Junctions, major reworks have to be done. By the way, does it matter that much? Mostly T-Junktions might appear in places that are either sharp edges or flat geometry, and in both cases it doesn't matter at all if geometry is properly jointed or not
(2022-05-04, 20:46)Magnus Forsberg Wrote: [ -> ]T-junctions
Might be necessary where 2 holes are close to eachother and using ndis is the better choise than tang prims.
But today we have tang, ndis and tndis, so avoiding T-junc is easier.

I would say that it can always be avoided. It might not be 100% tri/quad efficient but efficiency isn't the goal, render accuracy/quality is.

(2022-05-04, 20:46)Magnus Forsberg Wrote: [ -> ]Flat primitives
It is wrong to call them "Y-scaled". It would be better to talk about "flat prims scaled in three dimensions".

In their default, un-transformed state they lie on the X-Z plane. Therefore "Y-Scaled" isn't wrong. That said, if you have a better way to describe this state I'm happy to discuss it.
(2022-05-04, 20:51)Max Murtazin Wrote: [ -> ]I should mention that in some cases, for example axle primitives, T-Junctions are something that comes along with the way those primitives are made and how those are usually encased in other primitives. If we are going to get rid of any T-Junctions, major reworks have to be done. By the way, does it matter that much? Mostly T-Junktions might appear in places that are either sharp edges or flat geometry, and in both cases it doesn't matter at all if geometry is properly jointed or not

It not like we'll need to suddenly update the entire library. For the library spec (since it's a further restricted subset of the file format) if the spec changes the current, official parts are grandfathered in until they are updated for some other reason. A revision will only affect parts currently on the PT and and future submitted parts.
Thanks for clarification. Still tho, I don't see that much of a point in T-Junctions being disallowed by specs, because it demands change that doesn't affect basically anything as far as I'm aware.
(2022-05-04, 20:46)Magnus Forsberg Wrote: [ -> ]It is wrong to call them "Y-scaled". It would be better to talk about "flat prims scaled in three dimensions

It is the best way we have. Mind that flat primitive actually have to be scaled in 3 dimensions any time it isn't aligned with cardinal directions (relatively to the global coordinates)
(2022-05-04, 21:24)Max Murtazin Wrote: [ -> ]Thanks for clarification. Still tho, I don't see that much of a point in T-Junctions being disallowed by specs, because it demands change that doesn't affect basically anything as far as I'm aware.

Here's a couple threads on why (including the one where Travis convinced me I was wrong):
https://www.ldraw.org/forums/thread-8595.html
https://www.ldraw.org/forums/thread-2352...l#pid32836


Maybe I should have written "explicitly disallow unless justification is given".
Okay, I see now. Minding this, getting rid of T-Junctions is certainly a good idea, but keep in mind that it brings in some unpleasant problems that would meet to be faced later.
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