Re: ambient lightsource

["Thomas Helzle" <thomashelzle(at)gmail.com>]

Well, so far this is a distance shader and doesn't do ANY light calculations. I tried to made it very versatile with the 30 different falloff methods since I always try to write "once and for all shaders" instead of many shaders doing almost nothing ;-) , but what you want is something else :-)

That ugly 90° Terminator was one of the first things in XSI that made me write shaders for it (next to procedurals). For my own use, I have written a funny, 100% non-physical-correct-shader that shades over 180°, not just 90° and has built in gradients, custom highlights etc. - bye bye terminator. But since ALL MR shaders do only 90°, MR doesn't resolve shadows for such shading correctly (refer to one of the earlier mails where I linked to the Blender docs) and you get ugly black splotches. I seldom use shadows for my illustrations so this was never pressing enough to make me write a solution...
(BTW. I still dream of the availability of F-Curves in shaders, then you could build extremely flexible shaders with user defined falloff as in ZBrushs ZCurves - funny that doesn't exist.)

I forgot the link, but somebody wrote a 180° shader that is already available for free and for motiongraphics this will work just fine since you shouldn't need shadows too often. That should be what you want in combination with point lights with falloff.

For fun, you can also use the incidence shader in XSI, set it to Surface/Lights and to use 180°. While this doesn't calculate falloff, you can maybe combine it with AoN:Distance or try other combinations.


If I made you want to start writing shaders I am very happy. I find it very rewarding and I learned so much about how 3D really works from it. When I wrote my EasyGlass shader for messiah, I first just scratched the surface but bit by bit I implemented total internal reflection, absorption and many other things that I never _really_ understood before.  :-)

The Books on my website are my personal favorites - Texturing and Modelling (http://www.amazon.de/exec/obidos/ASIN/1558608486/thomahelzlges-21
)  was my first real step into shaderwriting almost 10 years ago and it is basically the bible for procedurals with all the industry pioneers explaining what they did from the ground up, Perlin, Musgrave, Worley etc. An amazing read.
Although I mostly use my own implementations nowadays, the basics are still the same as ever. Without Perlin Noise, almost no procedural in existance will tick. :-)
(just don't use the built in noise in the Mental Ray SDK - it must be the ugliest implementation I've seen so far.)
The 3D Math Primer (http://www.amazon.de/exec/obidos/ASIN/1556229119/thomahelzlges-21) was recommended by a programmer friend of mine when working at Passion Pictures in London for a short gig. It was the first book I have found that _really_ explains vectors, matrix math etc. in a human readable form with very good examples while being fun to read.
I have both next to my monitor as the main two books I use regularly. 

I recommend VC++ Express from Microsoft if you don''t have a compiler already - it is free, fast, has a very good IDE and does everything you need for shaders.

And leave the rants in. One shouldn't need to write those basic shaders or jump through math-hoops in the tree for such simple stuff. While MR is getting better and better in many areas (thank you master zap!), there is still a lack in the basics that I find hard to understand.
But I filled similar holes in messiah:studio with TLH:Pro - seems to be a common problem ;-)
(http://www.screendream.de/TLHPro/TLHPro_Documentation.rar
 if you are interested)

So just dig in and do it! :-)

Cheers,

Thomas Helzle

On Dec 3, 2007 5:57 PM, pingo van der brinkloev < pingo(at)pingofilm.dk> wrote:

Thomas. Man. The shader is awesome. It should be a base part of XSI.
you listening Softimage???

I have a request though (How typical to want more, Right?). Is it
possible to make it just react on all available light sources!?

This way I could actually make that image I posted, cause instanced
lights cast... well light!

So as it is (without Aon) I can make the spheres, with colored falloff
lights inside (don't even need Mograph). I make 3, spheres (R, G and
B) and XSI particles can randomize the size.
Only problem is: the Normals! there's this (obviously) 90° terminator
that's so annoying for CGI. So if Only your shader could be applied,
with the all lights trigger...?

And NOW look what you've done! You've made me want to look into shader
writing as well!!! dammit :-D

Are those books you're recommending on your site still relevant? (I
totally have to get a time machine and remove all my ranting in the
previous mails)

cheers !!!!

pingo

On 02/12/2007, at 19.46, Thomas Helzle wrote:

> Hi Pingo,
>
> now that looks fun :-)
>
> Give Helges MoGraph tools a good workout. Should be possible in
> minutes as well. :-)
> Particles from a spline, Randomizer, AoN:Distance maybe in the weird
> Object-Mode for automatic variations combined with Helges Random
> Colors...
>
> But what I found in my many years of software hunting: it is often
> very frustrating to recreate something from one app in another
> "exactly", especially if you are more experienced in one of them,
> since the toolset, strengths and mindset are so different. Helges
> MoGraph tools are superb and can do things C4D Mograph can't (I love
> meshtrails :-) ), but the other way around it's also true.
>
> In my experience, Mental Ray is never as fast with simple scenes as
> Lightwave or C4D, often it takes longer to just initialize...  ;-)
> But render Ambient Occlusion in C4D and you find yourself drinking
> more coffee than you ever should... ;-)
> Or several millions of polys...
> Or really large images in LW...
>
> So nowadays I try to concentrate more on the existing strengths of
> an app and use something else where it sucks ;-)  (or enhance it on
> my own if possible)
>
> The good thing with knowing many apps is, that you can think outside
> of the XSI-box, since you have actually _seen_ better solutions... :-)
>
> Well, let me know how the shader works for you.
>
> Cheers,
>
> Thomas Helzle

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