scott wrote:
>>> Ever heard of subdivision surfaces, Andrew?  You can get a perfectly 
>>> round sphere out of a plain cube cage by specifying up to 5 iterations.
>>
>> Yes. But the resulting surface can only be controlled by the 8 
>> original cube corners. That's not much control.
> 
> It's very simple to add in more control points, every time you want more 
> control you simple add in another point, this leaves you free to have 
> certain areas with very few control points, and other areas with lots of 
> control points, yet the result will be perfectly smooth.  For example 
> when modelling a car the large flat roof might only need a handful of 
> control points, but something around the wheel-arch might need many more 
> to get the curvature correct.
> 
> Another benefit is that you can instantly switch between the level of 
> subdivision, so you can have a 10 million triangle mesh for perfectly 
> smooth rendering, or a 100k mesh for use in a game, both coming from 
> exactly the same control points.

No, these are benefits of splines. If you have a surface described by 
splines, you can tesselate it to whatever resolution you feel like (or 
just render it normally). But if you have a triangle mesh, then you only 
have a triangle mesh. If you subdivide it, you now have only the new, 
higher-resolution mesh; you have lost the original. Now if you decide 
you want to edit it further, you can only do so in its new form. Sure, 
you could probably "un-subdivide" it, but no guarantees this won't 
completely wreck it.

> Watch this for a demo of it working (in BLender);
> 
> http://www.youtube.com/watch?v=ckOTl2GcS-E

I'm guessing I'm going to need audio before any of this makes sense. 
Maybe when I get home.

>> And yet, in all known editors, moving triangle corners around one at a 
>> time is the only available editing operation...
> 
> Haha, do you *really* think that people haven't thought of a better way 
> to edit triangle meshes? LOL

The problem is that, fundamentally, it's very hard to manipulate 
straight lines in a way that approximates curves. 10 years ago I used a 
couple of editors that would let you do things like move several points 
at once, or have a "magnet" feature where nearby points were sort of 
"pulled" towards where you're clicking, but the basic problem is that 
it's almost impossible to make anything good out of straight lines. 
(Unless, of course, you're actually *trying* to make something with 
straight lines - in which case it's fairly easy.)

For all the wizzy features of those editors of old, even creating an 
object as trivial as a banana was impossibly difficult. And, for some 
reason, modern editors seem to have drastically fewer tools to help. 
(Like I said, basically you can move points one at a time, and maybe 
scale / rotate the entire mesh, and sometimes you can increase or 
decrease the number of points automatically. That's not a lot to work with.)

Post a reply to this message