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p/low fast draft parts - Ben Supnik - 2014-01-08

Hi Y'all,

I was dusting off my notes on LOD when I noticed that octa-studs have already been moved to /8 in the official library, something that was discussed here.

http://forums.ldraw.org/showthread.php?tid=9745&pid=9745#pid9745

This gives us three levels of detail by searching /p/8 and /p/48 for primitives.

I would like to propose a fourth level of detail, designed to be the lowest quality rendering possible. Such rendering would have:
- No studs at all.
- No part interiors.

The LOD would be targeted for real-time viewing of stupidly-huge models, e.g. all of Datsville at once, etc. The goal is to preserve some vague shape and color of the model while bringing down vertex count as much as possible.

The goal would _not_ be to replace every single part with a simpler version, but rather to replace a subset of parts that are very commonly used (e.g. all of the standard dimension bricks, plates, etc.), possibly using a human-directed script.

In my past experimenting with this technique I found that a small number of 'draft' quality bricks could have a pretty huge impact on the weight of a model.

Anyway, if anyone thinks this is a terrible idea, or has strong feelings on how such a sub-set should be built, please let me know. I'd like to start putting a part set together.

Cheers
Ben


Re: p/low fast draft parts - Michael Horvath - 2014-01-08

Yes, we already use something like this for Datsville. See here:

http://home.swipnet.se/simlego/ldraw/ldboxer/ldboxer.htm

None of it is official unfortunately.


Re: p/low fast draft parts - Ben Supnik - 2014-01-08

Right - huge models like Datsville are the ones I am targeting!

BTW how long does the automatic LDBoxer take to process all of Datsville?

cheers
Ben


Re: p/low fast draft parts - Michael Horvath - 2014-01-08

Not very long IIRC.

I also made a less intelligent version of Tore's software that replaces all bricks with boxes regardless of whether the parts' tops and bottoms are exposed or not. You can find it here:

https://code.google.com/p/datsville/source/browse/#svn%2Ftrunk%2Fhelper_scripts%2Fmyboxer


Re: p/low fast draft parts - Philippe Hurbain - 2014-01-09

I don't think it's a bad idea, but some of your proposals (eg. remove inside) target parts, while the p/8 method concerns only primitives.


Re: p/low fast draft parts - Ben Supnik - 2014-01-09

Hi Philippe,

That's correct! Implicit in the proposal is that an LOD set could target for 'overriding' _any_ of:
- A part
- A sub-part
- A primitive.

In the original LOD discussion, Chris Dee commented in the context of octa-studs that he was "not (yet) convinced" about the need for this much substitution flexibility.

I think there is a strong case for part-overriding for such a low level of detail - my initial attempt at this indicated that we could get lower vertex counts at the part level tan by changing primitives by a pretty significant margin.

(From a theoretical standpoint, overriding parts and not primitives is needed when the LOD reduction in quality requires -merging- primitives into a single, simpler shape.)

I haven't specifically hit a sub-part case, but it seems odd to me to set up an overriding scheme that can override the primitive and part level and not the sub-part level.


Re: p/low fast draft parts - Roland Melkert - 2014-01-09

I like your lod ideas, but I'm afraid it won't work a good as one would think because the library is only extensively using subparts etc in the more modern (later) modeled parts.

At least this is my experience while adding snap info to the library the last couple of weeks. So to make things really well alot of parts need to be edited.


Re: p/low fast draft parts - Ben Supnik - 2014-01-09

Hi Roland,

We'll have to see what the real results are with some test files.

But again, my goal is not to produce a complete replacement of the library at LOD - my goal is to only replace "common" parts. My speculation is that on most models, a small percentage of the library results in most of the geometric output.

In other words, the payoff for replacing "Brick 1 x2 " will be high. The payoff for replacing "Minifig Head Nautolan, Black Eyes & Mouth, Brown Tentacle Bands" will be pretty minimal. :-)

Perhaps I can bug you for some of your large model collection to do some testing once I have a test library built up.

EDIT: I found my original post with stats...

http://forums.ldraw.org/showthread.php?tid=9663&pid=9663#pid9663

The large vertex cut-down for a relatively small set of parts changed was what gave me hope. While this was a -targeted- optimization (e.g. I modded parts based on the stats of my model) the parts I ended up modding were the usual suspects: standard, unpatterned bricks for the most part.

cheers
Ben


Re: p/low fast draft parts - Michael Horvath - 2014-01-09

For a test case, compare "datsville" vs. "datsville_boxed", here:

https://code.google.com/p/datsville/source/browse/#svn%2Ftrunk


Re: p/low fast draft parts - Michael Horvath - 2014-01-11

In addition to the low-fi parts I'd like to see the L3GO parts made "official" and updated. My 2 cents.