MoXi Digital Ink Painting System FAQ

(Last update by Nelson Chu, 26 April 2009)

For General Users:

Why do you make MoXi?

It all started in around 1995 - one day I realized that the combination of existing paint software (reads Painter) and graphics tablet just won't allow me to do Chinese calligraphic strokes. It's mainly because the brush technology then was (and still is) basically to use 2D shapes as brush footprint. I'm a user of Chinese brushes so I think I know what I wanted. Later, I had a chance (thanks to Dr. Tai) to really dabble in making a virtual brush and the result was published in 2002. With the success of the brush simulation, the obvious next step was to make virtual ink, although it wasn't obvious how to make a real-time system with the two simulated components of brush and ink. Luckily, recent hardware advances (GPU) came to the rescue and I'm glad that I also found a suitable simulation technique. The result was published in 2005 and this is the MoXi system you now see.

How long have you been working on this?

I started to work on it officially in 2000. Basically I spent three years for the brush and then two for the ink. Now I still continue working on it. The next generation watercolor tech is in the cooking.

Is MoXi already a product? Can I buy it?

No, the program is only a proof-of-concept prototype. However, it's already playable and can generate animations of ink effects. Whether it develops into a commercial product depends on further discussion with software companies/investors. If you're interested in investing on our technology, please contact us.

In September 2006, MoXi has been non-exclusively licensed to Adobe Systems, Inc. I also went to Adobe in 2006 to start the technology transfer. Please don't ask me when MoXi will get into Adobe's product(s) because I don't know.

In 2007, Sony Electronics Inc also licensed MoXi. I went to Japan to port part of MoXi to their new Cell Computing Board platform. I subsequently went to SIGGRAPH 2007 to demonstrate the ported program that simulates "suminagashi".

Would it be possible for me to get a copy of the current prototype?

Please note that we don't want to make our prototype public because it's not finished. However, if you have a good reason to have it, please send me an email for our consideration. In your email, please briefly introduce yourself (maybe show me your portfolio) and let me know why you want to use it now even when it's not finished. Please note that the prototype is NOT trial software. Please DON’T expect to get a copy by just saying “I’m very interested and want to try it!”  If you want to, say, make a short film using MoXi, we are more inclined to let you have it as your production could help promote us. Sorry, but we would only let people have the prototype for some very good reason. And I’m too lazy to reply everyone when we don't see a very good reason. Sorry about that.

In your email, please also assure me that you have the needed graphics hardware (see the next question and answer). Better still, let me know what GPU you have so that I can have an informal GPU survey. And, you should use a graphics tablet for input. We support up to six-degree-of-freedom input with Wacom Intous3 + 6D art pen. For the rest of the PC (e.g. RAM, CPU), nowadays most machines are good enough.

To Chinese readers:

Side note: If you want to buy a 6D art pen to use with our system, I have the following information for you. The current art pen has a felt-pen-like tip that is slanted. When you twist the pen, the point of contact with the ground is not fixed, making it a bit awkward to control subsequent movement. I'm trying to talk to Wacom about a design that works well with our paint system and hopefully they'd listen.

I don't have a capable graphics card to run your program. Which card should I buy?

The short answer is that you need a card in the Geforce 6 (except 6200) or later generations. The following is some performance data to help you decide which to buy. GPU is the chip sitting on the graphics card that does all those graphical processing.


Frames per second

 Geforce 6800 / 6800 GS

31 fps

 Geforce 6800 Ultra

42 fps

 Geforce 7800 GTX

61 fps

 Geforce 7900 GTX

70 fps

 Geforce 8800 GTS

85 fps

 Geforce 8800 GTX

120 fps

These data are recorded with the default settings (simulation resolution 512x512, d-scale 3). I'd say a frame-rate of 40 very good and over 70 excellent. If you're running MoXi with a GPU not listed above, please email me your frame-rate.

And you can see up-to-date prices for the nvidia cards on the right side of this site. You should also make sure the card interface is suitable for your system (i.e. whether it's AGP or PCI-Express). Most new systems would now use PCI-Express. If you're buying a new PC, I'd recommend a 8600 or 8800 (as of Nov 2007) depending on your budget.

Some of you may not be aware that GPU technology develops very quickly in recently years. The current top-of-the-line 8800GTX is too expensive for most users right now, but every year or so, new GPU's come out and the older ones would have their prices lowered substantially.

I don't have an ATI card. Thier ATI Radeon HD 3800 Series has floating point texture interpolation and is therefore capable of runing MoXi. Their Radeon HD 2x00 series has got "floating point HDR texture filtering", but I'm not sure if the filering also works for normal 32-bit floating point textues. If you own one, and would like to test it for me, please let me know.

What about Nvidia Quadro cards? Well, you will need some of the latest generations of Quadro like FX 4000 or FX 4500, Go1400 (i.e of the Geforce 6 or later generations).

Is MoXi actually used?

[CG Ainmation] A few production houses around the world have obtained our prototype and used it for some ink-related effects. One of them is Menfond Electronic Art Ltd, who used MoXi to produce special effects for this film (2005) - "The ink simulation is a whole new world for us to explore."


Flux Animation Studio Ltd used it for a few TV ads or MTV (2005-2006) - "Even in its 'proof of concept' stage, we were able to pull off effects and styles we couldn't have any other way!"

image004 image006 

spiderland.tv used it for TV ads (2006) - "We love MoXi!"


House of Curves used MoXi for a short film called "Losing Her" (2007), which was premiered at the fmx 2007. "We created a painterly backdrop, which we then 3d tracked into the live action plate using Syntheyes, and augmented with ink-bleed simulation effects courtesy of an amazing piece of software called MoXi."

[Digital Painting] A few digital artists has produced some paintings with MoXi (mostly running in no-flow mode) shown in this thread at IDA. One of them is Paulo Roberto Purim - "You're making history!"


Yoko Ogre reviewed our system and the review will be published in a Japanese online magazine (2006).

http://journal.mycom.co.jp/articles/2006/05/08/moxi/images/007.jpg http://journal.mycom.co.jp/articles/2006/05/08/moxi/images/008.jpg http://journal.mycom.co.jp/articles/2006/05/08/moxi/images/026.jpg

You can also see some paintings done by some kids here.

And Nelson would post artwork made with MoXi in his blog sometimes.

Is there a Mac version?

Sorry, not at the moment. This is technically possible as now Apple uses Intel processors too. But, a few users reported that MoXi won’t run on IntelMac under MS Windows. I guess it’s probably due to graphics card driver problem (as of 2006).

Can you do Western watercolor too?

Yes, and in fact, we've got some satisfactory results already. You can see some preliminary results here. In fact, the final product would also have dry media like pencil, chalk, etc.


For Technical Folks:

Why use a 3D deformable brush model?

3D brushes may not be necessary if you're painting in a traditional Western style. But in Chinese art, deft brush manipulation for making expressive marks is a significant part of the art. Nevertheless, it seems to me that painting styles are converging and such a 3D brush is for anyone who likes a digital tool that reproduces the spontaneous effects and happy accidents of a traditional brush. In recently years, I receive emails from all over the world concurring this. For instance, Daniel Morkowski from France says, "I find myself confronted, as you no doubt are aware, with the limited performances of the virtual tools currently available. Your research paper shows clearly that you understand only too well these limitations."

A 3D brush (together with a proper interface) also makes it more intuitive for new users to learn digital painting and gives a much better hint for the current brush footprint. For more argument, please read the second section of this article.

Why use fluid simulation for the paint model?

It's to make the paint behave more realistically. We want to make digital marks that look like real ones because people like seeing them that way. We can also modify the simulated physics to create new effects. On a computer, you can create a whole lot of effects that could be described in algorithms. Having our effects physics-based could make it more intuitive for the user because the simulated media would behave like some real materials that we are familiar with.

I want a CPU-only implementation. I don't want to rely on graphics cards.

Well, thanks to the blooming game industry, in a year or two most new standard PC's may be equipped with a capable graphics card. Don't you see some software giants are preparing or have already released software that exploit the power of modern graphics chips? If you are making your next paint software, you should really consider making use of GPU now. Things could happen sooner than you expect. :)

Your UI looks professional. What UI toolkit do you use?

MoXi was written with Borland Delphi. Using the VCL (the equivalent of MFC of MS VC++) to build GUI is so much easier than using MFC. I also use third-party components (all open-source) to build my program. See this page for a list of them. Now QT is free for the Windows platform for non-commercial use; you C++ folks may be interested in it.

For Artists, Art Critics:

Why go digital?

Reasons given by some digital artists include: 1. undo, 2. saving on materials expenses, and 3. saving artwork at multiple stages. Progressive painters looking for new art effects or tools may also find the computer a very good candidate for such a tool.

I also believe that the computer is a very good platform for bringing different art media together. How to give a sense of fluidity to oil painting? How to get strong colors in Chinese ink painting? It seems I already found the answers.

Can I use MoXi to train myself to do calligraphy with real brushes?

Let me use an analogy. Conventional calligraphy and digital calligraphy are like tennis and table-tennis. You don't use a table-tennis paddle to practice tennis, but I'm sure you will learn things common in the two sports if you play either one. You hold or use a graphics tablet stylus and a real brush differently, but you can at least practice character structuring in both digital and real calligraphy. If you can get the 'press-and-lift' rhythm with a digital brush, you should find it easier to do the same with real brushes.

Digital brushes are no good. Real art uses real tools.

Digital art tools are not meant to replace their real counterparts. At least I don't mean to. However, like different sports, you the users can choose which to play. As computers are becoming more and more popular, digital art tools may just become more and more popular.

Can I print artwork produced with MoXi on Xuan paper?

Yes. As suggested by Wucius Wong, I use a cheap inkjet printer for this task. Printer Ink can penetrates Eastern art paper much like real Chinese ink, giving the printout the look of conventional artwork. You can use unsized paper without unwanted ink spread because the amount of ink shoot from the printer jet is just enough to make marks at the right positions. One thing I'd complain is that the printer ink I use is not dark enough to give the unique feel of real Chinese ink. Another problem is that very thin papers like Single Xuan get creased easily, and I had to stick the paper onto a plastic sheet in order to make a successful printout. However, papers like Double Xuan or some paper from Japan (e.g.Moon Palace) do not get creased easily. Now I usually make economical printouts on cheap Japanese practice paper.

printout1 printout

The tablet stylus does not give me the force feedback that I'd get from a real brush. 

Yes, this is one of the main problems we still need to address. There is actually some devices that support force feedback, however they're not yet cheap enough for most artists.

The tip of the tablet stylus retracts only one millimeter or two. It doesn't give a true 3D control of the brush. 

That's true. However, I find it reasonably okay when I get used to it. Let's hope that hardware companies could soon give us more option on 6DOF input device.

Your results are impossible! I don’t believe it!

You really don’t believe it? I can assure you that we’re for real. No marketing hype here. If things go well, in a few years you will see at least one app using our technology and then everyone can try it for himself/herself. Please wait and see. If you’d like to see this happen sooner, get me some big investment. :) I myself always wanted to have digital paint tools free of charge or sold at a low price. I’m glad to see that other people (e.g. here) are starting to implement something similar.


After MoXi, what's next?

Nelson has PhD graduated in summer 2007 and left the university. He'd like to continue working on MoXi and is looking for opportunities in this connection. There are many things need to be worked on next. These includes Western watercolor and digital Chinese calligraphy. You can contact Nelson at hkideabrush@gmail.com if you have any proposal. See Nelson's blog for what he's up to.

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