Adding normals to the library

Adding normals to the library
So as I previously said about normals: no other single file format i've seen leave out normals to be computed by the user. There's absolutely no reasons not to include them. They're integral part of a geometry definition. Why forcing every single developer to reinvent the wheel, to spend countless hour on a custom smoothing algorithm? Algorithms that are already usually complicated, but more so for ldraw where definitions are sparse in multiple files, and one have to take into consideration hard and cond lines. I'm not a newbie of 3d programming (not a genius either by all means), and yet i've spent days trying to implement this algorithm and have yet to succeed. Of course i could spend some other weeks and do it, but why? And even if i did, we'll end up with many different programs, each one with its own algorithm, all slightly different, all buggy in a different way and with no consistency at all.

Updating all the library in not an easy task, but i think it can be done in a way that doesn't break compatibility and permits automatic data entry.

First off, i propose to add a new comment/command, with a standard sintax as follow:

0 NORMALS v1x v1y v1z v2x v2y v2z v3x v3y v3z [v4x v4y v4z]

It will be prepended to all quads and triangles, and will have three or four vertex definitions. Of course each one is the normal at the corresponding vertex of the face, in a per-vertex, per-face paradigm that is usually the standard.
Being a new comment, it will not cause any problem with existing software. Editors working with parts will not have any problem. Editors that write tri and quads may break the file but should not crash or misbehave themselves, and the user should be able to act on the problem. Hard and conditional lines can (and must) stay there of course.
New software developers can take advantage of the normals to achieve an uniform look across different renderers and saving weeks of head banging.

Now the delicate part: this solution assumes that any face have the same normals regardless of where it appears, or in other words that each single subpart/primitive always assume the same normals. But it may be that the same subpart can have different normals depending on the rest of the part it is attached to. If this is indeed the case, than it derives that it's impossible to add normals to a subpart as it can vary.
I'm not sure about this, intuitively each 3d shape should have its normals regardless of what it has around. Much of this maybe depend on the granularity of the subparts, how much down they break a solid. I remember that the primitives breask down even to 2d figures, which will need to be adressed somehow. In the worst case, the primitives would need to be rethinked with normals in mind.

How to popolate the library with normals

Ok, the problem of course is to inject all the normals in the already existing library. As the previous post, my solution is to take an existing smoothing algorithm, elevate it as the standard, and apply it to the whole library.

Basically it would work on a per-part basic. It will load the part and all the subpart into a canonical 3d model data structure, but mantaining a correlation between each face and the file/line that generates it. It will then apply the smoothing algorithm to the part, then traverse all faces and use the correlation to write them back in the source text. Of course some subparts will already have normals calculated (since they're shared), in this case the subpart can be skipped (or take advantage of the occasion to check if the would be calculated the same way).

Ok course normals are useful only if they're available on the whole part library (if a developer need to implement a smoothing algorithm for a single part, he may as well do it for the whole Smile ), this of course means that the library will grow in size, but i hope this is not an issue. Only subparts with actual faces will grow, but most of them should be reusing already defined chunks so will not grow. Eventually some optimization can be implemented (such as inserting a single vector instead of 3/4 if the face has uniform normals).
I'd love here some feedback for this humble proposal
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Messages In This Thread
Adding normals to the library - by Nicola - 2014-11-04, 13:31
Re: Adding normals to the library - by Nicola - 2014-11-04, 14:17
Re: Adding normals to the library - by Nicola - 2014-11-04, 16:12
Re: Adding normals to the library - by Nicola - 2014-11-04, 22:07
Re: Adding normals to the library - by Nicola - 2015-01-16, 16:07
Re: Adding normals to the library - by Nicola - 2014-11-04, 22:54

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