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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.)
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Invisible <voi### [at] dev null> wrote:
> But if you have a triangle mesh, then you only have a triangle mesh.
I think that the point is that nobody designs models using raw triangle
meshes. Instead, all models are designed using NURBS or other similar
spline-based surfaces which are easy to edit. The triangle mesh you see
in the end result has been automatically generated from those surface
models.
--
- Warp
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> 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.
No you don't. After you've seen the Blender video you will see what I mean.
The original data is always kept, and you can still edit it while the
subdivided triangle mesh is updated in real time.
> 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.
You use those "basic" tools to edit the original low resolution triangle
mesh. BTW in most packages you can at least select by vertex, edge or face,
and of course multi-select, then the obvious scale/rotate/move, also you can
extrude from faces and edges plus numerous more functions I haven't used.
The tools are designed *for* people to edit triangle meshes as their job,
once you've learned how it works you can do things quickly.
> For all the wizzy features of those editors of old, even creating an
> object as trivial as a banana was impossibly difficult.
It just took me about 1 minute to make a simple banana shape in Blender.
Blender even gives you a box to start with, so I just rotated the top face a
bit, scaled it down and extruded, then repeated 5 or 6 times. See attached
result - it's not hard, that model has ~2500 triangles and I can easily edit
the original triangle mesh (40 vertices) if I want to change the shape. If
I was going to do a big render I could knock up the number of triangles with
a click of the mouse, yet the original triangle mesh is still there to be
modified.
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Attachments:
Download 'image1.png' (10 KB)
Preview of image 'image1.png'
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Warp wrote:
> I think that the point is that nobody designs models using raw triangle
> meshes. Instead, all models are designed using NURBS or other similar
> spline-based surfaces which are easy to edit. The triangle mesh you see
> in the end result has been automatically generated from those surface
> models.
That would make a lot more sense, yes...
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scott wrote:
> also you can extrude from faces and edges plus numerous more functions I
> haven't used.
Care to define what "extrude" means?
> The tools are designed *for* people to edit triangle
> meshes as their job, once you've learned how it works you can do things
> quickly.
I've seen people who can take three sheets of paper, freehand scribble a
few lines on each page, drop one page on top of another and create an
instantly recognisable moving picture of Micky Mouse in life-like fluid
motion. That doesn't mean it's "easy".
>> For all the wizzy features of those editors of old, even creating an
>> object as trivial as a banana was impossibly difficult.
>
> It just took me about 1 minute to make a simple banana shape in Blender.
> Blender even gives you a box to start with, so I just rotated the top
> face a bit, scaled it down and extruded, then repeated 5 or 6 times.
I won't pretend I understand what you just said.
(FWIW, I *always* get Wing3D and Blender confused. But isn't Blender the
one that's supposedly impossible to learn due to the weird UI?)
Many, many years ago, AmigaFormat released a full version of Imagine 2.0
on a coverdisk. They ran a series of tutorials on using it. It had a
tool - I forget what it was called - where you start with a sphere, and
by moving the points in each of the 3 axis views, you could change the
profile and cross-section of the mesh. AF did a morphing tutorial where
you were supposed to use this tool to build an organe (so, an oragne
sphere then), a pear, an apple and a banana, and then morph from one to
the other.
(Unfortunately, the morph operation requires both start and finish
object to move the same number of polygons, and just linearly
interpolates them. BAD THING happen if the polygons are in a different
order in each model! But anyway...)
I wasted literally *days* trying to make these objects. They're all
absurdly simple, but I couldn't get them to look anywhere near right. It
was just far too hard.
As far as I could tell, Wings [I think that's the one I tried] doesn't
even offer this much help...
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> Care to define what "extrude" means?
Shifting a face in the direction of its normal, and filling in the gaps
between the shifted face and the other faces that it used to be connected to
(by automatically adding more faces perpendicular to the selected face).
Example in amazing 2D ASCII:
Start with 3 faces:
---.---.---
Extrude the middle face upwards:
.---.
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---. .---
Move the left vertex up a bit:
.
|\
| \
| \
. .
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---. .---
Extrude the top left face:
.--.
| \
| \
| \
.--. .
| |
---. .---
It's a very useful tool in 3D mesh design.
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scott wrote:
>> Care to define what "extrude" means?
>
> Shifting a face in the direction of its normal, and filling in the gaps
> between the shifted face and the other faces that it used to be
> connected to (by automatically adding more faces perpendicular to the
> selected face).
Ah, I see.
> Example in amazing 2D ASCII:
TMFT alert! ;-)
> It's a very useful tool in 3D mesh design.
I suppose...
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> HalfLife 2: Episode 2 has mist in one section. Looks really impressive...
> until it intersects something.
The quick way to get around that is to compare the depth value of the mist
you are about to render with the depth value behind, the closer they are
together the more transparent you make the mist. That way there is no
visible hard edge with the existing geometry. It's a hack of course, but it
looks a million times better than the hard edges, and doesn't draw your
attention immediately to "artifact". There is an example in the DirectX SDK
on this exact thing where you can toggle between different rendering
methods.
> Mind you, POV-Ray has the exact same problem, until you turn the settings
> up so high that it takes 82+ hours to render a single frame...
But at least you'll be sure it is 100% physically correct, ermmm no hang on
you'll need MCPOV for that, so make it 820+ hours for a single frame :-)
And don't even mention the time needed to tweak all the mist, dof and
lighting parameters to get it looking right...
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Invisible wrote:
> Care to define what "extrude" means?
Go to blender.org and watch the tutorial. Wings3D does the same thing.
It does exactly what you would think it does, given the name.
> (FWIW, I *always* get Wing3D and Blender confused. But isn't Blender the
> one that's supposedly impossible to learn due to the weird UI?)
Yes. Honestly, tho, it's not that hard. I picked it up with a day or two of
practice, got good enough to actually make a little anthropomorphic monster
type walk along, look around, and wave. It took a few days to get that far,
but it was the first package where I ever managed such a thing. I'm not
very good at it an I still managed in a couple of days to make something
work, limited more by my artistic skills than the tool.
> As far as I could tell, Wings [I think that's the one I tried] doesn't
> even offer this much help...
I found Wings much harder than blender, but I never went back and tried it
again. I think it has all the same operations as Blender at the basic level,
so I don't know why I found it so hard.
--
Darren New, San Diego CA, USA (PST)
I ordered stamps from Zazzle that read "Place Stamp Here".
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>> Care to define what "extrude" means?
>
> It does exactly what you would think it does, given the name.
No, I mean... I don't know what the word "extrude" means.
>> (FWIW, I *always* get Wing3D and Blender confused. But isn't Blender
>> the one that's supposedly impossible to learn due to the weird UI?)
>
> Yes. Honestly, tho, it's not that hard.
I gather they've been working on documenting it / making it was obscure
more recently...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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