Intro_Tuts_En.pdf

Blender Volumetrics

introduction tutorials

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)

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