Blender Volumetrics
Blender Volumetrics
introduction tutorials
introduction tutorials
Introduction
Introduction
Volumetrics represent an active field of development in Computer
Graphics (CG) dew to the broad field of application and the heavy
calculations that require the use and research of optimal algorithms to
minimize te calcule time. The usage of volumetrics range from CG
special effects to scientific data representation and analisis.
In 3D graphics the world are made generally out of polygons, forming
essentially hollow objects whichs fake the substance of it by using
superficial textures. This approach works fine for many situations in life
and should be encouraged as long as possible because its relatively
fast to represent, but some times the texture approach are impossible
because the internal structure of the objects does matter, that's where
volumetrics appear in the scene.
There's many approach to volumetrics and each one has its pros and
cons
1-Ray Casting
2-Texture Based (2D,3D)
3-Splatting
4-Shear Warp factorization
Also the classification could be according to the construction order:
1-Object order (Texture Based,Splatting)
2-Image order (Ray Casting)
Some methods could be implemented in GPU reaching realtime
performance at the cost of lower flexibility. In Blender, being a general
purpose 3d software running in many SO and in many hardware
configurations should have the most flexible yet quality volumetric
method, so the winner was Ray Casting, also for this desition the fact
that the ray caster are better integrable into the ray tracer based render
pippeline was taking into account.
 The spirit within
(Making a basic procedural volumetric)
a) Start a basic blender scene, a simple cube and toggles OSA off:
fig 1
You didn't expect that pressing a
button volumetric will be showed
up, dont you? The fact that an
object could have anything inside
of it prevent from that. ;)
First you need to tell blender that
you want to actually see inside of
the object,
that is, make the object some
degree of transparent (because
volumetrics are ray traced based
it should be ray transparency)
so lets check Ray Transp button
on Mirror Transp pannel (fig2): fig2
 b) Now you need to adjust the material alpha in order to see inside:
(fig 3)
Alpha 1 will give you solid objects
like default in Blender and alpha 0
with volumetrics on will give you full
volumetric objects without surface,
any value in between will give a
combination of both.
fig 3
c) Its time to define the inner material or sustance: go to the texture
panel and select for example Clouds, set NoiseDepth to 0 (fig 4)
fig 4
d) Now this is a really important stage, gradients are very important for
procedurals volumetrics and also provide a great level of flexibility, they
act like a clasification function. So before moving on in the Colors panel
activate Colorband button and adjust the values you want the
volumetric shows (fig 5):
fig 5
 The current implementation of volumetrics are texture controlled, so
any animation of the textures will animate the volumetric also.
e) Return to the material panel, under the Map input subpanel and
set Object and type: Cube (fig 6)
f)This is also very important, under 'Map to' set Col,Nor,Alpha on
(Volumetrics sample color,normal and alpha for every sampled point
in space) (fig 7)
fig 6 fig 7
Now its time for the magic to happen, blender knows so far that the
object are raytraced semitransparent, also knows that the inner
sustance its a cloud with a gradient and finally that the reference
coordinate system for the volumetric will be the object itself. This is the
basic setup before activate the volumetric button, this will show up 5
new pannels tabed according to its functionality:
1-Volumetrics (the main and basic pannel)
2-Quality (contains controls for raysplit algorithm and supersampling
algorithm)
3-Scattering (as the name says...)
4-VolShade (volumetric shading algorithms)
5-Models (specular and diffuse shading models)
 g) Focus now on the Volumetrics pannel (latter you will learn how to
use the more advanced features) and set the parametters as shown
bellow (fig 8):
fig 8
Step:
Set the sampling step along each ray, the lower the value, thebetter the
quality but increase render time, so the best option are initially choose a
relativelly big step: 0.1 or 0.05 and when you reach the desired
configuration lower it to the quality you want .
Dist:
This is the second important parametter in volumetrics: the distance
the ray travel inside the object sampling values, for now this is a fixed
value thus some effects could not be achieved until real ray travell
distance detection will be implemented, but this option will remain
because its usefull in many situations and also for the  window effect
(single side polygons showing volumetrics behind them like an open
window to the outside world)
Initially set this value low, because the longer the sample ray the longer
the render time (although early ray termination are implemented)
kr,kg,kb,ka:
Absortion factors for Red,Green,Blue,Alpha of each sample, adjust it
for different transparency/color effects
PreShad:
Toggles the use of preshading algorithm, since now that is the only ind
of shading algorithm implemented always should be set on (Post
Sading algorithm will be implemented latter )
Alpha Over:
This is the composite operator, Alpha Over are best suited for solid
volumetrics, others are Transparent,Simple,Isosurface,Range,MIPS
Well, that's all, hit F12 and render the cube, you should have something
like this (fig 9):
fig 9
If you only want to see the inside of the object then simply set alpha to
0.0
and deactivate the texture from the texture stack (this way superficial
texture won't be rendered and only the volumetric one will be showed)
(fig 10)
 fig 10
And the result is:
Now start playing with the different parametters and texture values,
even you can combine different textures to different mappings... the
posibilities are endless.
Here are some examples of the same file variating some texture
properties:
For questions and suggestions please write to me at:
[e-mail] with subject  Volumetrics+whatever-you-want ;)
[e-mail]
Farsthary
Farsthary
(Raul Fernandez Hernandez)
(Raul Fernandez Hernandez)