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The Volume Visualization operator adds detail attributes to the volume to allow for visualizations of volumes that requires multiple volumes to be joined together.
For example, one may want to take a density volume and color it according to three separate Cd.x, Cd.y, and Cd.z volumes.
There are two major components to the viewport volume visualization.
First there is the opaque smoke. This smoke occludes geometry behind it. It also casts shadows from light sources. Finally, a diffuse color can be specified for what light colors it reflects rather than absorbs.
A density of 1 means a density of 1 unit of smoke per unit of volume, this is will not fully block light.
Second there is an emissive, glowing, component. This field is added directly to the final image, washing out but not occluding geometry behind it. This is useful for fire-style effects. It can also be useful for visualizing data because it allows interior detail to shine through the outer layers.
Depending on your video card, you may see the emission be clipped to zero where ever there is no density. You can work around this by setting the density slightly non-zero everywhere.
Volume primitives have a built-in visualization mode. If a density volume is specifid, it will be overridden with this visualization mode.
The range of the density volume that will be remapped into the 0..1 range. This is the default range for all the other volumes unless the override is specified.
Fixed multiplier on the density field to control how opaque the volume is. If you are using a larger scene scale, you may need a smaller density scale.
Fog density is density per unit, and is independent of the resolution. So the same sized box, at 100 or 10 divisions, should be the same opacity. This means very small boxes will become transparent, especially if HDR rendering isn’t on. You can enable HDR rendering on the Effects tab of the Display Options dialog.
An additional multiplier on the density field, applied after the density scale, when the volume is used for lighting. This is the equivalent of multiplying the shadow intensity of all the lights by this value.
Max Vis Res
By default volumes are restricted to a maximum of 128 voxels on each side. This ensures reasonably fast shading times for lighting and avoids running into texture memory problems. This parameter lets you override this, either to make a lower res volume for faster previsualization, or to allow the volume to render with full resolution.
The name of the volume primitive to use for this operation. The value will be matched against the name attribute of the volume primitives to determine a match. * and ? can be used to allow for looser matches, the result will be the first matched primitive.
If this is a color field (diffuse, emission color), then if one volume is specified it is treated as a monochromatic field. If multiple volumes are specified, they are tied to the red, green, and blue channels.
Each field can have its own mapping range. The volume will be linearly remapped from this range into the 0..1 range.
Controls the use of the ramp. If set to No Ramp, the volume’s values are used unclamped and unaffected by the ramp. Clamped Ramp will clamp the volume’s values to the 0..1 range and then apply the ramp. Perioidic Ramp will take the modulus of the volume’s values with 1 and send that to the ramp. This can be useful to create checkerboard or striped effect to better see large ranges of values.
The volume’s values, after converting by the range specification, are looked up in the ramp to get the final value. If it is a color ramp then if there is one volume bound, that volume’s value is looked up to get the color. If two or three volumes are bound, each volume in turn is looked up to get the red, green, and blue values independently.
The following examples include this node.
This example demonstrates how the AttribFromVolume SOP can be used to transfer volume values onto point attributes.
This example demonstrates how you can use the Fluid Source SOP to source and advect colours from an additional volume into a smoke simulation.