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Menu rapide: Présentation du domaine — Portfolio — Articles et publications Voxel modeling: Claytools 1.3Below the surface
There’s never been a better time to be a sculptor, really. With tools like Mudbox and ZBrush, the once tedious process of modeling hi-resolution meshes has become friendlier than ever. So friendly in fact, that it has now appeal to the artists who were once reluctant to enter the digital medium. Of course, there is still the necessity for technical awareness, especially down the pipeline, when it comes to actually render the thing on a real time target platform. Nevertheless, the process of sculpting every details of a character or environment prop is a joy in itself, and now a job in itself. Yet there is still a pretty big drawback to the whole thing.
Whether you start from a primitive or a base mesh there’s still a limit to how far you can go, you cannot alter the geometry in any way you want. Try pulling a part too far away, and you’ll end up stretching the model. How about carving a hole through the whole piece? Booleans anyone? Naaah.
This comes from two postulates taken by these pieces of software. First, the sculpting tools are not entirely integrated within a standard modeling environment, which makes it difficult to alter the base mesh afterwards. Better integration is something we can certainly look forward from the makers of these programs in future revisions though.
Second, and the most important one, these pieces of software, like almost any third party programs out there, are surface-based. That means they are built from the ground up with surface description in mind, full stop. And rightfully so.
Invented in the late 70’s, the surfacic representation of object is the most efficient method ever invented for compressing data of a 3d world, given the fact that our own two eyes can only perceive light interaction with the surface of objects. Well, that actually only works for opaque, hard, continuous surfaces. Hence the difficulties to model with polygons some materials with complex surfaces and light (hairs, gas, refractive and transparent materials… etc). These have to use special techniques, and are still pretty difficult to achieve at real time frame rates.
So basically, it is a given to any 3d artists that 3d modeling is all about surface description. Well, not exactly. Here comes voxel modeling.
Virtual Clay
Voxel modeling is a modeling technique that doesn’t have any topological constraint. It doesn’t use polygons as the primitive for modeling, but it uses voxels instead.
Think about voxels as 3d pixels. Wouldn’t it be rather cumbersome if to paint an image you had to use a vector graphic package? No Photoshop, no bitmaps? Well that’s exactly what the traditional 3d packages offer, vector graphics.
Claytools, on the other hand, is the Photoshop of the 3d world, well to some extend at least. While still in its infancy, it already offers the sculptor the tools to play with the object’s inner matter, not just deform its surface.
You start with a bunch of clay (the name given to the matter in the package) that is composed of voxels, and use the various tools to carve, sculpt and add clay to your model.
At any time, you can split or merge any piece of clay. This is the beauty of voxels, no topological constraint, and unified data. You can create a library of pieces and then later blend them together at will. Top stuff when you’re used to the limitations of surfacic modeling.
Also provided are tools to manage patterns over the surfaces, project textures, and curves to extrude shapes and things like that. All within the voxel domain, this is tremendously powerful.
As with 2d images, you can resample the clay in both directions by changing the coarseness of the clay. Sample up and you can add more details, down and you get a more approximate version of your model. This is great stuff, besides the obvious sculpting abilities of the software, being able to ‘rasterize’ an imported mesh (.obj) to down sample it, filter it, and export it again is sometimes very useful, and provides very different results as compared to the classic angle-based polygon reducers.
To paint pixels in 2d, we are now used to work with a stylus and a tablet. However, to paint matter in 3d, you need a 3d device. Claytools comes with such a device, called Phantom Omni. This is the bottom range (and cheapest) of the 3d input devices manufactured by SensAble, the company behind Claytools, but it’s a well built piece of kit.
The touch generation
All right, I already hear the skeptics bashing about new gimmick devices and their preference to stick with their beloved tablet. Certainly the very same who would have preferred keeping their mouse for pixel painting when the tablets arrived in early 90’s.
The truth is if you want to move voxels around in true 3d (i.e. not just along surface’s normals) with a brush based tool, these devices are a necessity. Furthermore, a 2d tablet comes with the sense of touch as you touch the 2d surface, obviously. In 3d, this is another story as the surface changes as you sculpt the object. In order to give you the sense of touch, the Phantom Omni has built-in motors that provide force feedback as you touch the surface of the object.
While surprising at first, the sense of touch proves to be a great allied to perform certain modeling tasks which are difficult to achieve with traditional techniques. Erosion on a rock for instance can easily be achieved by moving a large carving brush over the surface, too large to enter small cracks; it will smooth out convex edges and avoid small cavities. To a certain extend, this is modeling with simplified physics properties.
Speaking about clay properties, Claytools provides shortcuts to change the clay’s hardness on the fly. You can then go from virtual butter to virtual stone as you sculpt, providing amazing combinations of techniques and results depending on the tool you’re using.
For instance, if you set soft clay and push it quickly from the inside you can create the impression of exploding matter.
I personally would like to see physics properties of voxels expanded in the future. The use of gravity and melting for instance could be awesome.
On a side note, I actually expect the physical voxels to become standard practice in real-time rendering in a couple of generations from now.
Think about this, surfacic modeling was invented for non-interactive rendering purpose. In games, the interactions with objects have been very limited so far because of the non existence of proper volumetric representation. Shoot a bullet in a wall and the only reaction is the display of an impact texture over it. Talk about realism. What about scattering and tearing of the bricks and mortar that are making up the wall? This can only work with proper volumetric matter representation. More than voxels, this is molecular modeling (voxels or particles with physical properties) ; something Jos Stam of Autodesk is already experimenting with the Nucleus engine for Maya.
I won’t go through all the cool tools that are built into Claytools 1.3, but there are quite a few, including very powerful curve functions. You can for instance use a curve on surface to extrude or carve an arbitrary shape. Remember, when you create a curve on surface, you actually feel the surface. And it is just the same for every snapping function, you actually feel the snap under the stylus, amazing.
Making hard edges and flat surfaces is somewhat difficult with standard surfacic sculpting tools. With Claytools however, you can carve out matter, as it was actually broken. This gives a look difficult to achieve with standard application.
In its 32 bit version, Claytools can work with up to about 20 millions voxels, largely enough for most usage. However, if required, there is a 64 bit version available which provides a virtually unlimited amount of voxels under the hood.
Voxels have this other advantage over polygons of being extremely lightweight. And it is surprising to see the very small memory footprint and file size when working with Claytools as compared with other applications.
Claytools is also one of the most stable tools I ever had the chance to work with. This is some serious programming going on there.
What’s next?
Some tools are missing for now in Claytools, like the ability to paint albedo (diffuse color) with proper brushes. Again, if we push it further, painting light transport properties at the voxel level could lead to stunning tools and results, imagine painting a jellyfish with internal structures. With GPGPU and the dramatic increase of parallelism in processing units, I’m sure there are already a number of things that could be implemented in this area.
SensAble is not only pioneer in the voxel modeling tools, they are probably showing us the path to the ‘next-next’ generation of real-time 3d graphics representation. They have the embryonic tool for volumetric data authoring that can today be used to generate surfacic data for current-gen usage. Hopefully, they will continue the development of this already fabulous tool and open the gates to fully volumetric objects creation. There’s still a long way to go, but it is a very exciting prospect to say the least.
The package is robust and the hardware well built, and even at a high $6000 price tag, it is worth every cent.
Meanwhile we can already enjoy the freedom of working with voxels with Claytools and simply export the result as an.obj file. With retopology tools such as TopoGun, creating controlled edge flows over dense meshes is now a snap and makes exotic tools such as Claytools a useful and powerful addition to our software library.
Franck.
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