Curve in Blender is a Mystery! How to turn Curve into Solid Pipe or Tube

Alright, today I wanted to talk and discuss a little bit about Curve in Blender.

Recently I have been using Grease Pencil and converting the Grease Pencil into Curve object. This workflow is very useful and many times we would like to turn Curve into some kind of Solid Pipe or Tube looking object for rendering. If you read my previous blog post, you have probably seen few different ways I would do that, whether:
1. I use Bevel and other curve (Circle) to sort of Loft the shape.
2. I use Extrude and Solidify Modifier.

Apparently, Curve in Blender has something more to it! It actually has hidden built in Tube/Pipe like maker. I just found out about it today. Let me just show you with an example.

Ok, as you all may already know, we could create controlled Curve either by:
a. Drawing with Grease Pencil and turning it into Curve
b. Drawing the Curve using Poly (extruding points) and then convert it into Curve.
(I will probably make video tutorial to just demo this.)

Anyhow, try drawing a Curve yourself, so you have something like this on the scene, a curve:

We got curve. Now we like to turn this into tube like object, and this is todays finding that kind of surprising. Take a look at Curve property on the Curve data panel on the side:

Focus on tab Shape and Geometry.

With Shape Fill checked for both Front and Back, increase the value of Geometry Bevel Depth to higher number than zero. You get something like this that resembles slides:

That is interesting. But here is another more interesting thing. Uncheck the Shape Fill for both Front and Back, you get something like this:

Its like a very low poly tube now (remember it is still Curve object). But very ugly with those random twisting happening. I have no idea why. But if you notice there is this 2D and 3D tab option, you can actually switch from 2D to 3D, and this will amazingly fix the twisting problems:

Cool solid 3D tube.

NOTE: At this stage, do not select 2D option or it will turn it into flat curve to the ground plane.

It does not stop here, because there is actually something interesting with this Curve. If you hit TAB and go to Edit Mode. Select a point or some points, and then press Alt+S (this is actually Shrink/Fatten option, UPDATE: at some point they suddenly called this Scale Feather), and do something like scaling, you could actually control the parameter of how this Curve turns into pipe! Instead of having all same size of pipe, you could have different size at any point, thinner or fatter. Something like below:

And you could also increase the resolution of this resulting Tube/Pipe by increasing Bevel Resolution. Try all the different options parameter under Curve Data and see what else you could find.

Now, like previous blog article, at this stage you could now add Build Modifier and see things grow. Very interesting and useful.

One more thing that I found:
If you are using this Curve dynamically as Force: Curve Guide for Particles, the way you have adjusted each point (to be fatter or thinner), will also affect how Particles would behave when following and traveling along this Curve. This is in fact an option that you could turn on and off, called Radius, inside Path Animation tab for each Curve. This has to be turned on if you like Particles to follow the Curve Guide force. The programmer/developer of Blender must have though about this. Not sure if they are actually documented. Maybe they do, but with Blender, often you accidentally found things like this by looking at other people video tutorials on the web.

So... there are apparently a lot about Curve that maybe we have not touched yet. Most 3D artist these days work with Poly anyway, but it is good to know something like this, can be very beneficial when modeling or certain effects.

I must do a video tutorial to show all this to make it clear. In the meantime, feel free to try it yourself :)

EXTRA:
Below is the original video tutorial (in Russian) that is kind of showing the whole thing, I cannot understand Russian, so I am kind of guessing by following the whole tutorial, but it opens my eyes a bit more:
http://www.blendermake.info/index.php/blender/111-put-dlya-particles.html

UPDATE 2011.11.30:
In Blender 2.6x and up, Curve object has been updated so you could now easily turn curve into a solid pipe, by just selecting one of the dropdown options:

Even easier, save lots of steps and times.

UPDATE 2012.02.08:
Even better, cap option is also added for Bevel.
http://www.foreverblender.com/2012/02/fill-caps-option-for-bevelled-curves.html

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