ePage Contents

 

Overview


The rendering process in Phoenix FD is separated from the simulation, but for ease of operation is performed by the same object that performs the simulation. However, this is only true for the grid's content, not for the particles contained in the cache file. If you want to render the secondary effect particles (foam, splashes, or drag particles), create a Particle Shader object and connect it to the simulator.

If you want to render the particle content of the Simulator (e.g. foam, splashes, or drag particles), create a Particle Shader | PHXFoam object and add the simulator to it.

Phoenix FD is able to operate in multiple rendering modes that can be divided into two main branches: volumetrics and surfaces. The volumetric modes are used for fire and smoke. 3ds Max materials can't be used to shade volumetrics, so their shading is described in the Fire and Smoke color rollouts. 

The liquid surface of a PhoenixFD simulation is generated from the Liquid Particles. The particles are converted into a mesh and shaded by the material assigned to the simulator object. This section contains the controls for this meshing process.

Advanced control over the shading is provided with the PhoenixFDTexture which can be used to drive the properties of a V-Ray material applied to a liquid surface. For Volumetric rendering, Phoenix FD provides you with the ability to drive the color and opacity of Fire / Smoke simulations through any of the supported channels (such as Smoke, Speed, RGB, etc.), as long as they are present in the cache files.

UI Path: ||Select Liquid Simulator | LiquidSim object|| > Modify panel > Rendering rollout

 

Actions


Render Presets... – Opens a menu for loading and saving different presets. The following options are available:

  • Load from File...
  • Save to File...
  • Default .aur Render Settings
  • Fire/Smoke .aur Fast Render
  • Fire/Smoke from FumeFX
  • Fire/Smoke .vdb from Houdini
  • Liquid .vdb from Houdini
  • Fire/Smoke .vdb from Maya Fluids
  • Fire
  • Fuel Fire
  • Gasoline Explosion
  • Explosion
  • Large Smoke
  • Candle
  • Clouds
  • Cold Smoke

 

Parameters


 

 

Mode | rendMode – Specifies the method for visualizing the grid content.

Volumetric – Visualizes the content as a standard 3ds Max atmospheric. This method is used mostly for fire and smoke.
Volumetric Geometry – This method requires V-Ray. 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 from multiple transparent layers. Note that the Approximate and Approximate+Shadows options for the Scattering parameter in the Smoke color window are not supported in this mode.
Volumetric Heat Haze – This method requires V-Ray. Produces the same result as the Volumetric option, but adds a heat haze effect when used with the Heathaze parameter.
Isosurface – This method requires V-Ray. It produces a procedural isosurface without polygons at render time using the Isosurface Level option. Compared to the Mesh mode, the result is always smooth but will take longer to render.
Mesh
–The content is converted into a standard 3ds Max mesh using the options in the Mesh Smoothing section.
Ocean Mesh – The grid content is extended to a flat area, fitting the camera's view. In most cases, this mode is used with displacement. Note that the ocean surface can be generated only when the liquid touches the sides and the bottom of the grid, which acts 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.
Cap Mesh – Only the upper liquid surface is rendered. This mode can be used for swimming pools and other placid liquid surfaces

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

Cutter Geom | usegizmo, gizmo – When enabled, rendering will occur only inside the selected geometric object's volume. Note that the Cutter Geom will not work when the render Mode is set to Volumetric Geometry.

Inverse Cutter | invgizmo – When enabled, rendering will occur 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 will be shaded as well. 

Invert Liquid Volume | solidbelow – By default, grid values above 0.5 are assumed to be liquid, and values below 0.5 are assumed empty. When enabled, the convention switches to the opposite such that values above 0.5 are assumed empty, and values below 0.5 are assumed to be liquid.  

Isosurface Level | surflevel - Allows you to specify a treshold value for the generation of the liquid surface. Grid cells below this value will be ignored. By default, the Isosurface Level is set to 0.5 and should only be modified if there is flickering in the generated geometry. Isosurface Level is used only in Isosurface, Mesh, Ocean Mesh and Cap Mesh Modes.

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.

 


 

 

Ocean


 

 

Ocean Level | oceanlevel – Used with the Ocean Mesh and Cap Mesh rendering modes. Specifies the water level as a percentage of the total grid height. 

  • Ocean Level is a rendering setting which is closely related to the Initial Fill Up simulation setting in the Dynamics rollout.
  • Both should initially be set to equal values, and the Ocean level should be adjusted after the simulation is done, if needed. This has to be done manually because the liquid surface might bounce up or down in the first few seconds until it settles.
  • Depending on a whole variety of factors, the resulting surface might be a little below or a little above the Initial fill up value, and this cannot be automatically predicted.
  • The Ocean level should remain constant and should not be animated for the duration of the render sequence, otherwise the horizon would start moving up and down.

Ocean Subdivs | meshsubdiv – Used with the Ocean Mesh and Cap Mesh rendering modes. When generating the far areas of the surface, this determines how many vertices will be generated for each pixel of the image. Like with V-Ray subdivisions, the square of the parameter value is used. For example, if you increase the subdivisions twice, the vertices count will grow four times. For more information, see the Ocean Subdiv. example below.

Increasing the Ocean Subdivs may dramatically increase the amount of consumed RAM.

Horizon Roughness | oceanhorizrough Controls the roughness of the distant ocean surface near the horizon. Adds more detail to the waves, which is especially helpful when using a highly reflective material for the ocean surface. Increasing this value can potentially produce visible noise when rendering an animation. To counter this effect, increase the Ocean Subdivs parameter.

Off-Screen Margin (%)oceanextramargin – The ocean is generated only in the camera view, which can lead to problems when using camera motion blur, using reflections, using refractions with Underwater Goggles enabled, or when the ocean casts shadows on objects underwater. This option allows you to extend the ocean further from the borders of the camera view in order to solve such issues. The value is a percentage of the image size.

Pure Oceanpureocean – Creates a flat ocean surface up to the Ocean Level height. It does not need loaded caches and if there are any, it ignores their content, so no simulation details will show. Thus changing frames and generating the ocean surface is very quick. This allows you to preview the behavior of the PhoenixOceanTex when Displacement is enabled or if you want to set up your texture for the Wave force. The option is available for both preview and rendering in Ocean Mesh or Cap Mesh modes. During preview, it requires the Show Mesh option to be enabled in the Preview rollout.

Underwater Goggles | uwglasses – This option is designed to be used when the camera is placed under the water in Ocean Mesh or Cap Mesh mode. When enabled, a few polygons are added in front of the camera, and the grid content is kept outside of the resulting mesh. The result is similar to real underwater goggles in that the field of view shrinks.

Example: Ocean Subdivs


 

 


Ocean subdiv. = 2

 


Ocean subdiv. = 8

 

 

 


Mesh smooth




 

Smoothness | smoothmesh – Specifies the number of smoothing passes. The higher the value, the smoother the result, but the mesh will require more time to calculate.

Use Liquid Particles | useprt – Enables particle-based smoothing of the mesh. It requires Liquid particles to be simulated and exported to the cache files. This method overcomes the limitations of the basic smoothing without particles, which can flicker in animation and cause small formations in the mesh to shrink.

Particle size | prtsz – Used to make the liquid thicker or thinner. Works only when Use Liquid Particles is enabled. This parameter specifies the distance from the mesh surface to the particle centers.

 

Motion blur


The Motion blur of the mesh is obtained by shifting each vertex along the velocity by the shutter time. To render your simulation with Motion Blur, you need to enable Velocity channel export from the Output tab of your simulator. Furthermore, if rendering a Liquid simulation with Foam, Splashes or Mist, you would also have to enable Velocity export for each particle system under the Output → Output Particles tab.

 

 

Multiplier | mbmult – Specifies a multiplier that affects the strength of the motion blur. This value can be a negative number. 

Prevent Self Intersection | mbself – In certain cases, the shifted vertices might penetrate the opposite side of the geometry. When enabled, this option prevents such situations. The self-intersection analysis is expensive, so enable this parameter only when an intersection is obvious.

Phoenix meshes are motion blurred in a different way than regular transforming and deforming geometries. 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, for each rendered frame, a new Phoenix 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 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 the preceding or following frames is not used, unlike regular deforming meshes. As a consequence, the liquid and the objects in your scene would synchronize best if those objects do not use additional geometry samples for motion blur.


Displacement

Displacement is a technique intended to add detail to the simulation during the rendering. The idea of the displacement is similar to the usual geometry displacement: a texture is sampled, and the corresponding point on the mesh is shifted in a direction at a distance determined by the texture. You can plug both V-Ray and regular 3ds Max texture maps, as well as the PhoenixFD Ocean Texture. 
You can use the Phoenix FD Simulator's Mesh Preview option to check how the attached displacement map is affecting the surface when rendering a Liquid simulation.

 

 

Displacement | displacement – Enables the displacement effect.

Map | displ2 – Specifies the map used to displace the fluid. Depending on the Type option selected, a monochrome map or a color map could be required. If a colored map is specified when a monochrome map is needed, the strength of the displacement is determined by the total intensity of the color. If a monochrome map is specified when a vector map is needed, the entire displacement will point in a single direction.

Multiplier | displmul – Specifies the displacement amount.

Vertical Fade Level | fadebylevel, displfade – Specifies a vertical zone above the Ocean Level, where the displacement will be strongest. Above this zone there will be no displacement at all, and inside this zone the displacement will gradually be reduced moving up from the ocean surface. This is needed so that the ocean displacement would be applied only near the ocean surface and not to any simulated fluid splashing high above the ocean surface. This parameter is a percentage of the grid height, just as the Ocean Level option.

Fade Above Velocity | fadebyvel, displvelfade – If the fluid velocity (in voxels/sec) in a voxel is higher than this value, there will be no displacement at all. When the velocity is lower than this value, the higher the velocity, the weaker the displacement will be. This allows you to suppress displacement for the fast moving parts of the fluid where the displacement would visibly disturb the motion in an unnatural manner, and thus you can have only the still ocean surface displaced with waves. This option requires the Grid Velocity channel to be exported to the simulation cache files from the Output rollout.

The Fade Volume feature can be used when the liquid is in contact with a geometry surface such as a shore or a ship and the displacement breaks the contact by moving the liquid mesh away from, or into the geometry.

Fade Volume | usefadeobjfadeobj – When enabled, allows you to specify a geometry object as a fade volume. There will be no displacement inside this object and outside it the displacement will be gradually reduced at a distance specified by the Volume Fadeout Distance parameter. 

Volume Fadeout Distance | displgeomfade – Specifies the distance in world units around the object where the displacement will fade out.