# Pragmatic VEX: Volume 1 [4K] [H18.5]

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Hand translated Korean subs are almost finished

Courtesy of Seona Hwang!

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Some feedback from Alexander Vasilyev (Technical Artist @ Ubisoft) on Artstation

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Pragmatic VEX is listed as part of the official VEX learning path! Thanks SideFX!

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Celebrating 1 year anniversary of Pragmatic VEX: Volume 1!

Since its inception it has been a huge success among the high end VFX studios and artists alike.

And for that I am hugely grateful!

Therefore it will be on a discounted sale for a week until August 20 12 PM PST.

Enjoy!

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To celebrate the yearly anniversary, I decided to share the Limit Surface Sampling chapter from the course (5 separate videos). AFAIK this topic has never been covered by other tutorials, so I hope it proves to be useful for your work! Enjoy!

To generate interpolating surfaces for other subdivision schemes we need a method of determining the position and the normal at a set of points on the limit surface. Because the surface is the result of repeated application of a subdivision step, we can analyze the behavior of a small neighborhood of points as they converge to the limit surface in order to determine the surface properties at the point of convergence.

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There is a very practical use of the limit surface to figure out where a point is on the subdivision limit surface.

Imagine a character head like the one we were using, and you add a lot of detail to it, just like what we did before using adaptive subdivision.

That sounds all good in action, but what we are missing is the future projection of the same geometry, by additional subdivision, either as a post operation before exporting out the geometry, or as a render time operation.

In any case, this will result in the areas where there is added detail, to be flatter than before, even though it's not the case without adaptive subdivision.

Because if you recall, we were using Catmull-Clark subdivision algorithm, which will keep the original geometry nice and smooth.

But in other cases where you might have additional detail using algorithms such as Bricker, it might result in the areas where there is added detail to be flatter than before.

But we don't necessarily want this. What we want is to create detail without disturbing the future subdivided shape of the geometry.

So how can we do this?

Evaluating attributes at the subdivision limit surface gives us a way out.

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If you have access to the subdivision limit surface by patch IDs and the patch UVs, then surely you can scatter points on the limit subdivision limit surface just like you scatter points on a polygonal surface.

And this is exactly what we are gonna do in this chapter.

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When we are talking about creating a lot of points, we can not avoid pre-generating them for maximum performance. It might not always be applicable but when it is, the performance gains can be quite significant.

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Pragmatic VEX: Volume 1 has been updated to Houdini 19 to ensure it shows the most up to date methods available in the latest version of Houdini. Enjoy!

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Pragmatic VEX is featured on ASUS ProArt showcase series! You can see the Supercharged extension in action.

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Pragmatic VEX is featured on ASUS ProArt showcase series! You can see the Supercharged extension in action.

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