In-order for objects in 3ds max to be rendered as volumes with Arnold, the object mesh has to be converted to a volume, and a Standard Volume material assigned to the object:
Add an Arnold Properties modifier to the object.
Under Volume set the Step Size to a value higher than 0.0.
Assign a Standard Volume material to the object and set it’s parameters to design the volumetric effect:
* Note that both Density and Depth control the transparency or ‘thickness’ of the volume. (lower Depth setting creates a thicker volume)
* When Scattering is set to 0.0 the volume will have only a absorption effect
In this example an Arnold Noise map is connected to the Standard Volume‘s Density parameter:
* Note that the Scale values must be set correctly in order to actually get a ‘cloudy’ effect.
* Note that the noise color values are now controlling the Density of the volume.
An example of a basic traditional (not scanned) cloth material setup in Arnold 5 for Maya using an aiStandardSurface shader.
The shading network uses a classic angle dependent color blend to simulate the color of the cloth being washed out at grazing angle of view.
Explanation of the node graph:
A black and white fabric weave texture that will serve as input for multiple shading channels.
* This is actually not the best example of such a pattern, and could be replaced with a much better texture.
A remapValue node is used to set contrast to the fabric pattern (reduce contrast in this case) prior to it being multiplied with the fabric colors.
* Note that only one of the textures RGB channels is connected to the remapValue node since it’s a float (mono) processor and not RGB.
* Note that depending on the fabric texture, you may have to design different curves to achieve the right effect.
Two colors are defined with colorConstant nodes:
A deep color as the main fabric color, and a washed out color for grazing angle view (“side color”).
An aiFacingRatio node is used as an input for incident angle info.
* Note that in this case I checked the node’s invert option to make it behave more like other systems I’m used to (if you don’t use invert, the angle blend curve in 5 will be different..)
A remapValue node used to set the angle blend curve or in other words, how much does the color appears washed out per change of view angle of the cloth surface.
* The longer it take the curve to become steep from left to right, the more the main color will be dominant before the washed out color will appear.
A colorCorrect node is used in this example just as a way to convert the remapped float value back to RGB for being multiplied with the cloth colors.
* We could also connect it directly to the individual float components of the RGB colors but this way the node graph is cleaner.
A multiplyDivide node is used to multiply the processed fabric texture with the 2 fabric colors “baking” the pattern into the color.
A blendColors node is used to blend the 2 processed fabric colors together according to the processed facingRatio angle input.
The result is the final cloth color that is connected to the aiStandardSurface shader.
An aiBump2d node is used to convert the fabric pattern to normal data that will be connected to the aiStandardSurface shader to produce bumps.
An aiStandartSurface shader serving as the main shading node for this material.
* Note that under Geometry the Thin Walled option is checked so that the Subsurface layer of the shader will act as a Paper Shader rather than SSS.
* The main cloth color is connected to the SubSurface Color input.
The Arnold Standard Surface Shader’s Transmission Scattering options can be used for simulating highly realistic volumetrically ray-traced sub-surface-scattering suitable for materials like wax, soap, milk etc.
While the Transmission Depth attribute controls volumetric light absorption within the object (fog), the Scatter attribute controls what percentage of the light will be scattered instead of absorbed, effectively creating the murky effect of semi-transparent materials.
Note that for the scattering effect to work Scatter must have a dominant percentage value, and the Depth attribute must generally be much lower (shallower) than what would create coloring without scattering, otherwise the object will continue to look transparent and lacking the internal substance that we want to simulate.
Also note that the Opaque attribute must be unchecked in the Arnold attributes of the object’s shape node for the light to be able to pass into the mesh and illuminate the volume.
*This is actually a “cheat”, because physical semi-transparency has to be simulated by indirect light calculation or caustics, but for dense volumes like wax it’s very effective and the loss of realism is insignificant.
Arnold’s Ambient Occlusion (dirt) node can be used as a procedural mask to create interesting material effects like in this example of paint that is eroded at the model’s bulging areas to reveal metal beneath it.
In this shader’s case the Ambient Occlusion node is connected to the Mix property of an Arnold Mix shader, that blends between two different Arnold Standard Surface shaders, one simulating the underlying tin metal, and the other simulating the red paint that covers it.
Note that in the Ambient Occlusion node the Invert Normals property is checked, so that the effect will create a mask for the bulges and not for the creases,
And also that the Self Only property is checked so that the node will behave as a fixed object mask disregarding the proximity of other objects.
In this example the output of the Ambient Occlusion node is also process using a Remap Value node to increase it’s contrast so it will define borders between the areas.
In the camera shape node’s Arnold Attributes:
Check ‘Enable DOF’.
Set ‘Aperture Size’ and ‘Focus Distance’ to control the effect. Note: The Aperture Size attribute isn’t an f-number aperture like we would expect in photography but a radius in world units.
Larger Aperture Size values (larger lens Iris opening), and shorter Focus Distances will cause a narrower Depth of Field which will result in the background appearing more blurry.
DOF is generally more apparent with ‘long lenses’ (shorter focal length).
Set other Aperture attributes like the number of blades and aspect ration to further design the appearance of out of focus areas and especially highlights.
* The optical effect referred by the term ‘Bokeh’ in photography.
The Subsurface component of the Arnold Standard Surface shader (aiStandardSurface) controls Sub Surface Scattering (SSS).
When the ‘Thin Walled’ option is checked in the Geometry attributes of the shader, the Subsurface isn’t rendered as a full volume of material like soap or skin/flesh (the effect that is traditionally called Subsurface Scattering – SSS) but as a thin paper-like translucent surface like paper, thin cloth thin leaves, lamp shades etc. (the effect traditionally called Translucency or ‘Paper Shader’)
* Note that this option is suitable mainly for polygon surfaces without thickness (just one side)
To create a Translucent shader with Arnold:
Subsurface Weight must be higher than 0.0 for the effect to be computed.
In Geometry, check Thin Walled for the SSS to be rendered as Translucency (Paper Shader).
Use samplerInfo Node Facing Ratio output in Subsurface weight to add realism by changing the weight by angle.
Multiply weave texture with Facing Ratio to simulate fabric translucency.