Fluid Attributes

Additional V-Ray attributes can be added to fluid shape nodes in Maya. If these attributes are not present, the default volume shader will be used, and the shading quality will be determined automatically, taking into an account the "Quality" fluid attribute and the cell size. Note that there isn't an exact correlation with the shading quality of the Maya Software renderer.

With V-Ray 5.0 Maya Fluids render physically correct, i.e. they appear darker. The original look from previous V-Ray versions can be replicated by adding the V-Ray fluid legacy Phoenix FD shading attribute and then turning on the Legacy Phoenix FD Shading option. Phoenix FD and Volume Grid nodes have backward compatibility so Fluids made with older versions of V-Ray show no change in behavior. See the Rendering with Older Assets page.

UI Path: ||Select fluid|| > Attribute Editor >  Attributes menu > VRay > (select attribute set)

Volume Shader – Determines which volume shader to use.

Phoenix FD – Uses the Phoenix FD shader which is optimized for grid based volumetric data.
VRayEnvironmentFog – Uses a generic purpose volumetric shader that V-Ray is using in VRayEnvironmentFog node.

Scatter GI – Enables the tracing of GI through the fluid. The standard GI engine in the V-Ray settings is used.

Scatter bounces – When Scatter GI is enabled, this attribute limits the number of GI bounces that are calculated inside the fog. It can be used to increase the rendering performance.

Simplify textures for GI – When enabled, V-Ray uses a simplified method for calculating the GI when rendering parts of the liquid that are textured or that are being faded out.

Step size – Determines the size of one step through the volume of the liquid. Smaller steps produce more accurate results but are slower to render. In general, dense volumes require smaller step sizes than more transparent volumes.

Max steps – (VRayEnvironmentFog only) Specifies the maximum number of steps through the liquid. Its purpose is to prevent too many steps inside the volume. However, it can cause parts of the fluid to not render!

Texture samples – (VRayEnvironmentFog only) Determines the number of texture samples for each step through the liquid. Thus, textures are sampled more accurately than the volumetric lighting. It is useful in cases where the textures vary much faster than the lighting itself (e.g. for detailed fractal textures). Note that this parameter is used only with the shader.

Cut-off threshold – Controls when the raymarcher stops traversing the volume. If the accumulated volume transparency falls below this threshold, the volume is considered opaque and tracing is aborted. Higher values make the rendering faster but may introduce artifacts.

Subdivs – (VRayEnvironmentFog only) Determines the number of points inside the fog at which volumetric lighting is evaluated. If this value is 1, a single sample along the ray is calculated, otherwise, the Step size is used instead.

Diffuse color multiplier – Specifies an extra multiplier for the diffuse lighting. This can be used to produce a non-physically correct result. The VRayEnvironmentFog shader requires this parameter to be set to 4.0 in order to produce a result similar to the Maya Software renderer. The Phoenix FD shader does this automatically.

Jitter – Used to offset the starting point of shading in order to hide regular patterns.

Solid mode – When enabled, the fluid is rendered as a solid object with a sharp surface, determined by the Solid threshold attribute.

Solid threshold – Specifies the value below which the fluid is assumed to be "solid."

Volume Light Cache – (Phoenix FD only) Enables the use of Light Cache data. This can increase the performance but can present lighting splotches, especially when used with a low resolution grid and noise textures.

Full Motion Blur – Turns on the motion blur caused by the fluid movement inside the container. This is slower than calculating only the motion blur of the fluid container.

Disabled – Disable to increase the rendering performance.
Blend – Uses simple fade out between two states of the fluid. Note that this actually produces a fluid moving effect.
Velocity – Uses the velocity field to actually move the fluid in the time. Since this method is using a snapshot of the velocity at the start of the motion blur interval, the end position often does not correspond to the start of the next motion blur interval.
Velocity + Blend – Uses the velocity to try blending more accurately between the current and the next frame. This is the most advanced, but slowest method.

Render as Geometry – Enables the fluid to be rendered as a collection of semi-transparent geometric layers. It allows to output render elements (without it you will see only Alpha and RGB), as well as to generate deep image data when saving to Deep EXR or VRST.

Enable Rendering – Enables/disables the rendering of the fluid.

Create Fire Lights – When enabled, allows the fire to shine on smoke and on surrounding objects in the scene even without using Global Illumination (GI). With GI, the fire will automatically illuminate the other scene objects and the fluid's own smoke, but the rendering will take quite long. Enabling Create Fire Lights simulates GI by placing light sources in the bright parts of the fire, which produces similar results and renders much faster. 

Light Power on Scene – Controls the light intensity over all scene objects except the fluid itself.

Light Power on Self – Controls the light intensity over the fluid's own smoke. This does not change the intensity and color of the fire itself; only the illumination over the smoke is affected.

Self Shadowing – Enables self-shadowing of the smoke from the fire's light. If enabled, the smoke obstructs the path of light from the fire, creating a much more realistic look but decreasing rendering performance. To gain back the rendering speed, set Self Shadowing to Grid-based and decrease the Light Grid Resolution (%) parameter to reduce the number of generated lights.

None – Smoke does not obstruct the light propagation and it is brightly lit.
Ray-traced – The simulator's smoke is illuminated by the fire's light sources using precise but slow ray-tracing. Note that the fire lights always illuminate the rest of the scene using ray-tracing. This mode is physically correct and takes into account non-transparent obstacles inside the volume, but requires intense computation and can take considerable time to render and clear the noise from the image.
Grid-based – The self-illumination of the smoke is calculated separately from the light that the fluid casts on the scene using an approximate fast formula. Unlike Ray-traced, this mode does not produce noise and the resulting illumination on the smoke is always smooth. However, any obstacles inside the volume are ignored by this mode and will not cast shadows on the smoke from the fluid's own light. The Light Grid Resolution (%) parameter can be used to lower the resolution of the light grid and further speed up the illumination process. Reducing the grid will generally produce smoother self-illumination. Note that using Grid-based self-shadowing requires additional memory, so beware of high RAM usage with high resolution grids or many copied or instanced volumes.

Light Grid resolution (%) – Specifies the resolution of the light grid as a percentage of the fire grid's resolution. Perfect illumination from fire could be achieved by placing a light in each fire cell, but this could take a tremendous amount of time to render and such accuracy is usually not necessary to approximate the fire's illumination convincingly. In order to speed up rendering, a separate light grid is created internally which can have a lower resolution than the fire grid, and this light grid is populated with one Omni light per each cell. The lower resolution (and thus fewer lights) speeds up rendering at the expense of some illumination detail, which might not always be visible anyway. At a value of 100, the light grid has the same resolution as the fire grid. The smaller the Light Grid Resolution is, the smoother the illumination becomes and the faster the rendering is. However, at very low values the fire might not blend well with the light it casts on the smoke.

Light Cut-off – This parameter works the same as the V-Ray Light cutoff parameter. It specifies a threshold for the light intensity, below which the light is not computed. This can be useful to limit the effect of the light to some distance around the fluid container. Larger values cut away more light; lower values make the light range larger. At 0.0, the light is calculated for all surfaces, but the rendering could slow down significantly.

Create Lights when not Renderable – When enabled, forces the fluid to emit light over the scene even if Enable Rendering is disabled. This can be used for compositing when the fluid is rendered in a separate pass.

Legacy Phoenix FD Shading – When enabled, fluids render with old behavior from previous versions of V-Ray.