First
off, I'd like to say a big 'hi' to all my friendly
rivals participating in the current (as of May
1st) competition on the 3Dtotal forums. This tut,
although possibly not that viable for your final
entries, is for you ;D
Oh, and Tom, I've promised you some tuts in the
past, so this should make up for it ;D
I
came up with this cel shading technique while
in a period of boredom and a concept art drought.
it concentrates on the issues of other cel effects
(like not being able to cast shadows, or having
an intelligant outline). This technique should
be easily ported to most other 3D packages if
they have an algorithmic, light/shadow sensitive
falloff routine. I can't port it, since I'm not
rich enough to to be able to afford LW, or Maya,
etc and can't really do it at 'work' or school.
Anyway, on with the tut!
1.
- model: here we have our base model, created
concentrating on silhouette, and body mass,
as opposed to topology - just a slightly
different way of making a cartoony mesh;
nothing special. It's subdivision btw.
2.
- lights: I've rigged a simple lighting
setup, making sure I've got some shadow
and nice luminant gradients from 0 (black)
to 255 (white). this is just to test out
all the elements in this technique.
3.
- base material: OK, this is the first real
step in this technique. Seeing that you'll
be wanting solid bands of shading, and maximum
control (especially if you're doing a large
scene) this will minimise hassle later on.
Go into the material editor ('m') and create
a stand-alone falloff named 'shading luminance
base'. This will be used to create all the
solid blocks of shading. Change it to 'shadow/light'
falloff type and make sure that black is
in the top slot, and white is on the bottom.
Now
change the mix curve so that there's 4 points
going like this:
1- x:0 y:0
1- x:0.45 y:0
1- x:0.55 y:1
1- x:1 y:1
now insert a copy of this falloff into it's own
2 slots. in the black slots falloff make the colours
top=black and bottom=dark to medium gray. the
mix curve should be:
1- x:0 y:0
1- x:0.2 y:0
1- x:0.3 y:1
1- x:1 y:1
for the black slots falloff make the colours top=light
gray and bottom=near white. the mix curve should
be:
1- x:0 y:0
1- x:0.7 y:0
1- x:0.8 y:1
1- x:1 y:1
Of course, you can change all this at your discretion,
it's just a guide. You can add more or less shading
bands, or change whatever the you want. One thing
to try out is using much sharper gradients and
enabling a supersampler to filter the aliased
shading bands. ups the render time, but you can
use more extreme forms of shading (huge long shadows
for instance). I ended up switching to this later
to get more of an authentic solid band than the
softer look; it's all to do with what style you
want.
blech! enough of the numbers already...
4.
- shading materials: Now create a new standard
material (mine is 'skin base shader'). Put
up self illumination to 100%, no gloss/spec
and put the diffuse colour to a medium/average
of what you imagine the final will look
like (this is just to help you out in the
viewport).
next
insert an instance of the 'shading luminance
base' into the diffuse slot. There's two
ways of colouring here. An easy to control
globally way, or a more tweakable but no
global control way. For the easy to control
one, insert this falloff into a RGB multiply
mat and simply tint it with the desired
colour. you can then change the luminance
values on all the materials in the scene
by changing the base luminance shader and
they keep their respective colours. For
things like skin though, where you want
to have some meaty red translucency where
it's a base skin colour at the light source
and more pinkish towards the darker areas
or the such, then you use the second way
which is simply using a copy of the luminance
base and manually changing the colours in
it. Your first shading material should look
something like this:
repeat
for any other materials.
5.
- black outline: Make a simple material
that is jet black in the diffuse, no gloss/spec
and 100% self illum. OK, the trick in this
technique is so simple, but surprisingly
very hard to visually get a stuff up it's
frightening ;D unlike virtually all the
other cel shading techniques out there that
use visually incorrect methods to create
the outline in the material, mine uses a
mesh base.
Create a referance clone of you object that
your cel shading at the same position of
the normal mesh and apply the black material
to it. On this referance, add a push modifier
then a normals modifier. My push is set
to around 5.5 but of course this is subject
to scale differences. Set the normals modifier
to flip normals, and looky there; you've
got an outline - even in the viewport! Make
sure you turn off cast shadows on this referance
too so you don't get shadow artifacts -
unless you've got a huge outline and the
shadow wont fit properly that is.
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6.
- conclusion: now then, what makes this so great
in comparison with all those other cel shading methods
out there? well it's near as perfect as you can
get in visual output with a clean, default max.
It's simple to use, easy to create, and not that
intensive to render out. It has the least amount
of limitations, and the most flexible and versatile
methodolagy meaning you can add hatching, doodling
or any other type of effect easily (as seen in the
last picture).
Why not use a gradient ramp set to lighting you
say? well some tuts do, but that means it doesn't
output shadows, and is therefore useless for most
applications. Why not use a secondary material or
another falloff as the outline instead of another
mesh? well that ALWAYS screws up on anything besides
a sphere; try doing that on a cylinder and looking
diagonally down on it - see, screwed ;D
Like anything in the world, there's something that's
not quite right, making it prone to some form of
abnormality. There's a whole heap of scientific
and philosophic laws conspiring against the world
to make that happen - so blame it on the scientists
and philosophers ;D . Although minimal, in this
case, it's that sometimes the outline can make thin
antialiased lines when looking at extreme angles
(this isn't really a stuff-up, just something that
you may not be wanting for the style you're going
for. It needs a minimum thickness cut off). umm...
oh yeah, another is that the border mesh should
be closed/capped and shouldn't have any holes as
these make inverse lines (they curve the wrong way
and you can see it's a normals flipped mesh). that's
all I can think of and that I've seen... no real
drawbacks, or limitations if your mesh is made 'correctly'.
What about animation you say? well because it's
a reference, it'll deform to whatever you change
the original to + then apply the normal and push
modifiers. An easy rig is to either link, group,
or even attach it (although I don't recommend attaching...
too much work in most scenarios if you're planning
on doing skeletal animation or similar).
Here's
some other examples of what this can be used as
a basis for (I thought I'd put the wireframe and
bitmap based ones there as well to prove it's
not a photoshop filter ;D ):
Comments,
criticism, and sexual advances can be directed
to mathius@geeklife.com If anyone discovers any
other problems or limitations, please don't hesitate
to contact me... oh, and my spelling isn't wrong,
I'm Australian - and that's not an illness ;D
