Versions Compared

Old Version 6

changes.mady.by.user Kristina Gaytandzhieva

Saved on

compared with

New Version Current

changes.mady.by.user Kristina Gaytandzhieva

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

The Volume Grid is able to operate in multiple rendering modes that can be divided into two main branches: volumetric and surfaces (Isosurface, Mesh, Ocean Mesh, and Cap Mesh). The volumetric modes are used for fire and smoke. Cinema 4D materials can't be used to shade volumetrics, so their shading is described in the Fire the Fire, Smoke Color, and Smoke Opacity rollouts rollouts. The surface modes can be used for some interesting fire-related effects, like freezing flame or cartoon-style smoke. Unlike the volumetric modes, surface modes have no dedicated shader; they use the material applied to the Volume Grid.

...

UI Text Box
typetip

For a list of supported Render Elements, please check the Render Elements page.

You may also check the Volumetric Rendering In-Depth guide for tips on speeding up the rendering of volumetric effects with V-Ray.

...

 



Rendering

Section
Column
width60%

Enable Rendering – Enables/disables the rendering of the Volume Grid.

Anchor
renderMode
renderMode

Render Mode– Specifies the method for visualizing the grid content. For fire/smoke, you will want to select a Volumetric method. For liquids, select a geometry method.

Volumetric – Visualizes the content similar to a an Environment Fog. This method is used mostly for fire and smoke.
Volumetric Geometry –  Used to export deep images and render elements such as normals, velocity, multi matte, etc. It produces the same result as the Volumetric option by using procedural geometry made up of multiple transparent layers. Note that the Approximate and Approximate+Shadows options for the Scattering parameter in the Smoke Color tab are not supported in this mode. 

UI Text Box
typenote

Approximate and Approximate+Shadows options for the Scattering parameter in the Smoke color window are not supported in Volumetric Geometry mode.

For a complete list of the supported Render Elements in both Volumetric and Volumetric Geometry modemodes, please check the Render Elements page.

Volumetric Heat Haze –  Produces the same result as the Volumetric option, option but adds a heat haze effect when used with the Heat Haze parameter. Note that you might need to increase the Max Depth of a V-Ray Material with refraction , in case it intersects with the Heat Haze shader.
Isosurface – Used mostly for liquid simulations. It produces a procedural Isosurface geometry using the Surface section options. Compared to the Mesh mode, the result is always smooth but will take longer to render.
Mesh – The content is converted into a standard mesh using the Surface section options. This mode is mostly used for liquids but can be applied to thick smoke using a scattering material or to plumes of smoke to create effects such as large underwater bubbles.
Ocean Mesh – The grid content is extended to a flat area, fitting the camera's view. In most cases, this mode is used with a displacement texture such as the Phoenix FD Ocean Texture.
Cap Mesh – Only the upper liquid surface is rendered. This mode can be used for swimming pools and other placid liquid surfaces.

UI Text Box
typenote

The ocean surface can be generated only when the liquid touches the sides and the bottom of the grid, which act as a container for the liquid. The detail of the mesh extension around the simulator depends on the camera resolution - for each pixel of the viewport or the rendered image, one or several polygons are generated, depending on the Ocean Subdivisions option.

 


Step % – – Specifies the ray marching step of the camera rays as a percentage of the cell size. As the renderer traces rays through the Volume Grid, this value controls how often to get information from the grid. If this value is more than 100, some cells start getting skipped, and artifacts can result. If rendering volumetrics with a specific transparency curve, a lower percentage might be necessary so that fine details are not lost. On the other hand, increasing this value increases the rendering speed. This parameter is used when when the Mode is set to Volumetric, Volumetric Geometry, Volumetric Heat Haze, and Isosurface modes. See the Step % example below.

Shadow Step % | shadowStep – Specifies the ray marching step of the rays used to evaluate the lighting (shadow rays) as a percentage of the cell size. Usually, this value can be higher than Step %, as generally, shadows do not need so much detail. Increasing the Shadow Step % also speeds up rendering performance, particularly with dome and area lights.  

Border Fade – – Makes the content near the grid's boundaries more transparent to prevent sharp edges from being rendered. This parameter controls how far from the boundaries the transparent effect should start , in scene units.

Sampler Type | rendSamplerType – Determines the blending method between adjacent grid cells.

Box – Displays cells as cubes. There is no blending between neighbor cells. This is the fastest mode.
Linear – Linear blending occurs between neighbor cells to smooth out the fluid's look. Sometimes this mode may unveil the grid-like structure of the fluid. Up to 20-30% faster than the Spherical option.
Spherical – – Uses special weight-based sampling for the smoothest-looking fluid. With increasing resolution, the visual advantage of this method over the Linear method becomes less noticeable.

Motion Blur Multiplier – Specifies a multiplier that affects the strength of the motion blur. May also be a negative value.

UI Text Box
typeinfo

To render your simulation with Motion Blur, make sure that your cache files contain a Velocity field and that it is properly remapped to the internal V-Ray Volume Grid Velocity channel in the Input → 3rd Party Channels Mapping dialog.

UI Text Box
typewarning

When rendering regular meshes with motion blur, the entire mesh is moved along its transformation path back and forward in time, and so each individual vertex of the mesh follows this path. However, when rendering a meshed surface, for each rendered frame a new mesh must be built from the voxel grid, and so it usually has a different number of vertices than the previous and the next frame. Because of this, individual vertices can not be traced back or forward in time between frames. Instead, motion blur of fluid meshes uses the velocity of vertices, which is recorded by the simulation , and moves each vertex back and forward in time along the vertex velocity. This is why the generated liquid mesh does not support frame sub-sampling for motion blur. This may cause a mis-match mismatch between the liquid and transforming/deforming objects in your scene that interact with it. The fluid mesh is generated from data at the exact rendered frame, and fluid data for from the preceding frame or following frames is not used, unlike regular deforming meshes. As a consequenceConsequently, the liquid and the objects in your scene would synchronize best if those objects do not use additional geometry samples for motion blur.

Velocity Texture – Specifies a custom texture used for motion blur when rendering Fire/Smoke simulations. The colors of the texture represent the velocity direction for each cell, similar to how Vector Displacement textures are evaluated. Every simulator cell receives a certain color from the texture, treats it as a direction vector, and stretches the contents of the simulator along to produce motion blur. This parameter can be used with a V-Ray User Color texture for motion blur in a single direction(e.g., by setting the color to (0, 1, 0) for motion blur in the +Z axis) , or any other Maya texture applied as a 3D projection. The texture overrides the Velocity grid channel even if available in the cache files. Note that the Y and Z components of the velocity vectors are flipped - they are sampled respectively from the Blue and Green color values of the texture.

Column
width3%

 


Column
width37%

 

 

 




Anchor
renderStepJitter
renderStepJitter

...

The first render, which has a Step % value of 90, took 3m 2s to complete. The second  second render, with a Step % value of 900, took 2m 13s to complete. Increasing the Step % speeds up the render, but it reduces detail.

Before after
afterLabel900
beforeLabel90
Panel
borderStylenone

Panel
borderStylenone

...


...


Example: Heat Haze

This example shows how Heat Haze adds refraction at each ray-marching step through the volume. This only affects the camera's view. Heat haze will not affect shadows cast through a volume. In this example, the Render Mode is set to Volumetric Heat Haze, ; the Surface Grid Channel Name is set to Temperature_phx, and the Isosurface Level is set to 0.5. Heat Haze is set to 10. Border Fade is set to 250. All other options are left at their default.

Before after
afterLabelOn
beforeLabelOff
Panel
borderStylenone

Panel
borderStylenone

...


Surface

...

Section
Column
width60%

This section controls the conversion of the grid content into geometry. If Render Mode is set to Mesh, Ocean Mesh, Cap Mesh or , or Isosurface, the Surface channel channel needs to be set, and an appropriate Isosurface Level must be chosen from this section.

The controls in this section also denote the surface used in Gradient and Surface-driven displacement. This way it can affect all render modes, not just the surface modes.

The technique for generating the surface is based on the isosurface concept concept. The resulting surfaces are mostly used to render liquids , but can be used for smoke and fire as well to create effects like underwater bubbles, freezing fire, etc.

Surface Channel – Specifies the channel that defines the surface of the fluid. It is used for solid rendering and displacement.

Texture - The values of a custom texture will define the liquid surface.
Grid Channel – Allows one of the grid channels to define the liquid surface.

Temperature_phx - The Temperature channel defines the liquid surface. Temperature is typically in the range 0-1 for Liquid simulations and 600-2000 for Fire / Smoke simulations.
Smoke_phx - The Smoke channel defines the liquid surface. Smoke is typically in the range of 0-1 for Fire / Smoke simulations.
Speed_phx - The Speed channel defines the liquid surface. Speed channel output has to be enabled for this to work. Speed is calculated as the length of the velocity vector for each voxel.  
Fuel_phx - The Fuel channel defines the liquid surface. Fuel channel output has to be enabled for this to work.
Viscosity_phx – The Viscosity channel defines the liquid surface. Viscosity channel output has to be enabled for this to work.

Surface Texture – If the Surface Channel is set to Texture, this slot specifies the texture. In Mesh, Ocean Mesh, Cap Mesh and Isosurface render In Mesh, Ocean Mesh, Cap Mesh, and Isosurface render modes, the selected map will completely replace replaces the cache files that have been loaded, if any.

Isosurface Level –  Allows you to specify a threshold value for the generation of a threshold value for generating the geometry surface. Grid cells below this value are ignored. Isosurface Level is used only in Isosurface, Mesh, Ocean Mesh, and Cap Mesh Modes.

Invert Volume – – By default, the values above the surface level are considered internal. When enabled, this option swaps the inside and outside.

UI Text Box
typenote

The proper value for the Isosurface Level parameter depends on the numerical range of the surface channel. For example, Phoenix FD liquids are kept in the range of 0 to 1. A value of 0 means there is no liquid in a certain voxel, and a value of 1 means the cell is 100% full of liquid. Values in between indicate a certain mixture of air and liquid. For such cache files, an Isosurface Level value of 0.5 is best for visualizing the surface between the air and liquid. 
Imported caches from Houdini, on the other hand, use positive and negative values to indicate whether a voxel is inside or outside the liquid volume, so a correct "halfway" Isosurface Level value would be 0.0. 
For Phoenix FD Smoke, the proper value is about 0.01, and for Phoenix FD temperature, which is in Kelvins, the value is several hundred.


Use Render Cutter – When enabled, rendering will occur occurs only inside the selected geometric object's volume. If Fire Lights are enabled, only those inside the cutter will be are rendered. Note that this will this does not work when the the Render Mode is set to Volumetric Geometry.

Cutter Geometry – Specifies a polygon geometry that clips the rendering only to inside its volume.

Invert Cutter – When enabled, rendering occurs only outside of the render cutter. This is not the same as a cutter with inverted geometry because any rays that do not intersect the cutter are shaded as well.

UI Text Box
typeinfo

If using a Render Cutter for a liquid pouring into a glass or otherwise contained into in another refractive object, you may need to set the Render Mode to Isosurface. By default, the mode is set to Mesh, which may produce artifacts in the rendered image.

Column
width3%

 


Column
width37%

 


...

Example: Isosurface Level

In this example, a Phoenix .aur file of a liquid simulation is connected to the Input parameter. The Render Mode is set to Mesh. The Surface Channel is se set to Grid Channel, and the Grid Channel Name is set to Temperature_phx. Mesh Smoothness is set to 1. All other parameters are left at their default state. Use the sliders to preview the Volume Grid as a mesh (when rendered) and as a voxel preview (in the viewport). Keep in mind that changes to the Rendering rollout are not reflected in the voxel preview. To change the voxel preview, use the Preview rollout.

 

 



Section
Column
width30%
Image slider
minLabelMesh
maxLabelVoxel

Isosurface Level = 0.1

Panel
borderStylenone

Panel
borderStylenone

 
Column
width3%

Column
width30%
Image slider
minLabelMesh
maxLabelVoxel

Isosurface Level = 0.5

Panel
borderStylenone

Panel
borderStylenone

 
Column
width3%


Column
width30%
Image slider
minLabelMesh
maxLabelVoxel

Isosurface Level = 0.9

Panel
borderStylenone

Panel
borderStylenone