Question for the Hard-Core MR users: line wobble

[jdoubles]

Hello everyone, I will be up-front in my ignorance toward Mental Ray: I really know nothing. However, I have a unique challenge for anyone willing to help me out:

Can I get a "line wobble" effect by modifying the contour shaders in Mental Ray?

I have successfully used MR to achieve the toon-shaded effect, but the contour lines are too perfect, and obviously Computer Generated. To make 3D toon shaded animation look more like 2D cell animation, the line wobble is crucial. When artists draw lines in animation, they dont use rulers, so there are many small variations in the line that is often refered to as line "wobble." I need to accomplish the wobble effect in addition to the toon shaded effect and I'm hoping some creativity with MR will do the trick. I want to interfear with MR's contour store and contour contrast utilities to cause it to draw a wobbly contour line. I have looked at the C source code for these utilities and noticed that it draws the contour by repeatedly collecting two points along the edge of some geometry and drawing a line between them. I figure if I can intercept the points, I can add or subtract some values to cause MR to wobble the contour line. So this is my theory, but I have no idea how to implement it. Where can a noob like me go to learn how to modify the existing C code in the contourshade.c and outimgshade.c files? I can program in C no problem, but how do I recompile the code on a Windows platform and test it out in maya? Can you guys think of any other creative ways to achieve this line wobble (and varying the line width doesnt accomplish the same thing as wobbling the line). Any advice you can offer would be most excellent, even if it's as simple as a link where I can learn how to code, compile and import my own C++ code into Maya. Thanks so much, Please help!

         -John Doublestein
          web.ics.purdue.edu/~jdoubles

[failure]

Render contours as separate pass and "wobble" them in post using one of image deformation filters. You can also add other kinds of "trashy" effects. For example contour flicker by simply animating the output level.

[jdoubles]

I've considered wobbling in post, but wasnt happy with the results. You guys have any other ideas on doing this with mental ray? Thanks!

[failure]

May I ask what have you tried in post?

[jdoubles]

I've been using after effects to experiment with filters and masks to achieve the desired effect. I've gotten the best results with the ripple filter, and plugging in some random number expressions to make sure each frame has different characteristics. However, while it's easy to distort the lines, the distortion always comes from a central point, even if I move the central point around. What I really need to do is have the distortion track along the contour line so it applies the ripple just like someone would draw the line. If you dont track along the line, parallel lines or lines that are close to each other have the same distortion/wobble, which doesnt look hand drawn, but looks like someone just applied a filter. That's why I was asking about breaking into the mental ray contour code, because I could make the wobble by modifying some code while Maya was drawing the line, saving me from having to write some code to detect the contours and track along them after they're drawn. So, here's the problem again: How can I take the contourshade.c and outimgshade.c files, recompile them with my changes, debug the code and then reimport it into Maya to use with rendering? If you guys have any ideas on how to modify the contourshade.c and outimgshade.c files to achieve a wobbly line, I would love to hear that too! Thanks everyone, I'm looking forward to hearing your ideas, I think this is a really neat problem to solve.

[failure]

If you don't know "kow to code" then don't bother with it. c++ cannot be larned in short time from tutorials - at least not to a level where you can succesfully modify some serious piece of code.

Even if you try to change the code - your idea with just randomizing the pixels or projected vertices won't look good either. You'll need some quasi random function to make it look good.
What you talking about is basically a 2d opearation so it doesn't really matter who does it - shader or post filter - it's pretty much the same because it happens on already projected pixels.

So drop that idea and do it in post. I assure you that it's doable with good results - just invest more effort. Try to use image driven displacement filters.

And you can alyaws output the contours as postscript data using contour_ps output shader. Then batch process the ps frames using some vector distortion filter in illustrator.

[joojaa]

Another computationaly heavy way would be to slightly displace the surface in normal direction with soome noise and edge detect that for edge jiggle.

[joojaa]

Another computationaly heavy way would be to slightly displace the surface in normal direction with soome noise and edge detect that for edge jiggle.

[suzanne-irving]

Mr jdoubles
You say that you have had success in MR rendering to get a flat catoon effect, but too perfect. Could you give me some tips on this. I don't mind if its perfect. I am very new to MR and rendering and have been trying to sort out the toon shade thing with not much success. Could you help or point to a very current tutorial that covers it all clearly. Right now I have had no succes but read a lot of posts, all saying very different things. using 6.
thanks

[joojaa]

Yes, its a bit hard to follow if you only read forums because the way it used to be done is very different from the way it is done in maya 6.0 and 6.5. And people do take time to update their knowlege, thats why one should look ain the manual first (or in this case ist skipped allmost entirely because the new explanations rare much more easy to follow leaving you only with the old way explained, wich will confuse the hell out of most users altough the steps are allmost identical).

1. Create objects (i persume you have allrerady)

2. assign them with materials.

3. Then open the attribute editor for your material and find the shading group tab for it (mental ray specific stuff is stored here for some reason)! Expand the menytal ray section and check enable contour rendering, set yoru line width and color.

4. open render globals for mantalray and expand contours contours check enable contour rendering, you may fiddle with theese setttings as you wish, but usualy you want around coverege and between different instancess set. Along with some depth contrast say 3-10 depends on you scale, and normal contrast of about 15-90 depending on the effect

Manual reference wich describes how and what the knobs are:

http://localhost:4446/Maya6.0/en\_US/WhatsN...rrendering.html

[bobmorane79]

on his site http://jonhandhisdog.com
jason schleifer explain how to make this effect with a curve an expression

[joojaa]

You mena the jiggle cache bake thing? Well yes it makes for wobble. Actualy i tougght the user only wanted worbble on the lines! BUt hey wobble thge entire thing works a s fine. but its not bneccerserily the exact effect this poster is looking for.