Table of Contents

This page provides information on the Preview rollout.


The parameters in this rollout control the representation of the fluids in the viewport. All enabled values are drawn if the content is within the specified range.


Expand – Opens a floating dialog that contains the selected rollout and automatically folds the command panel rollout.

Re-Center – Resets the position of the floating rollout.

? – Opens up the help documents for the Preview rollout.

Read Cache for Preview  | prv_read_cache – Allows to completely disable reading of cache files in order to speed up the viewport. When cache files are not read, neither voxels and particles, nor the grid bounding box or the Cache File Content under the Frame Info rollout are shown. This way scrolling the timeline is quick as there is no access to hard disk or the network. If you still need to see the grid bounding box and the Cache File Content info, you can leave this option to Always, and instead disable all voxel preview options, the Mesh PreviewGPU Preview and all particle previews. The intended use for this parameter is as a last step performance optimization.

Always – Cache files are always read by the preview.
Don't Preview Caches – Cache files are never read for the preview. They are only read during rendering.

Detail Reduction | prv_dwnsmp – Decreases the grid and particle detail in the preview. A value of 0 means no reduction. Increase this value if the interface starts to lag due to the simulation being very large. This parameter controls both the viewport preview and the GPU preview.

Auto Reduction | prv_autoreduct  Enables automatic adjustment of the Detail Reduction parameter. The preview detail is reduced up to a point where the preview displays fast without blocking the interface. Note that the detail only decreases automatically, but does not increase.

Only if Selected | show_only_sel – When enabled, the viewport preview is only drawn if the Volume Grid is selected.

Active View Only | prv_avonly – When enabled, the contents of the cache file are only shown in the active viewport.

Show Box | showgrid  – When enabled, displays the Volume Grid's loaded cache bounding box in the viewport.

Graph Cells | gridcells – When enabled and Show Box is enabled, displays a lattice with the cell sizes on the sides of the Volume Grid's box.

Show Mesh | showmesh – When enabled, shows the Isosurface as a mesh. The Isosurface  is defined in the Surface section of the Rendering rollout. This mode overrides the Voxel Preview mode. Note that if Mode is set to Ocean Mesh in the Rendering rollout settings, the surface is generated in the viewport with low mesh resolution in order not to slow down the user interface significantly.

The Volume Grid can only preview the channels present in the cache file for the current frame. To see the list of available channels and their ranges, go to the Cache File Content section of the Frame Info rollout.

GPU Shade Preview

Show | gpu_viewport – Enables the GPU preview in the viewport. Note that geometries that intersect the Simulator box or are inside the simulator might appear completely behind the entire fluid or in front of it. Another limitation of the viewport preview is that it is not visible if the camera goes inside the Volume Grid.

Exclude Lights – Launches the GPU Preview Light Include/Exclude List window which can be used to specify which light sources to be used for lighting.

Ambient Lighting | gpu_ambient – Specifies the color of the ambient light. 

In order to get proper shading for the smoke, the light source has to have shadows enabled, including atmospheric shadows. Otherwise, the smoke is rendered as flat and featureless.

V-Ray lights have these settings enabled by default.

A 3ds Max light, such as an Omni light, must have its Shadows On, Shadow type set to VRayShadow (or Ray Traced Shadows if using the default Scanline renderer), and Atmosphere Shadows On.

Voxel Preview

Only the Overlap Of: | prv_and – When enabled, shows only the cells where the following selected channels overlap.

Temperature | prv_temperature, prv_t_threshold, prv_t_threshold2, prv_t_color, prv_t_color2 – Enables the representation of the temperature. 

As Fire | prv_plank_t – When the temperature is in Kelvins, e.g. when coming from a Phoenix simulation, the voxel colors come from a physically correct black body radiation model. In this mode the custom color for the temperature are disabled. Check the Grid Channel Ranges for more info.

Smoke | prv_smoke, prv_smoke_threshold, prv_smoke_threshold2, prv_smoke_color, prv_smoke_color2  – Enables the representation of the smoke. 

Fuel | prv_fuel, prv_fuel_threshold, prv_fuel_threshold2, prv_fuel_color, prv_fuel_color2 – Enables the representation of the fuel. 

Velocity | prv_velocity, prv_v_threshold, prv_v_threshold2, prv_v_color, prv_v_color2 – Enables the representation of the velocity.

Velocity Streamlines | viewVelStreamlines, viewVelStreamlinesThreshold, viewVelStreamlinesThreshold2, viewVelStreamlinesColor, viewVelStreamlinesColor2 – Traces the velocity field of the cache files to generate a streamline preview.

As Rainbow | viewVelStreamlinesColorCurve – Represents the Velocity Streamlines in rainbow colors, where red is the fastest, green is medium speed and blue is the slowest.

Lines Length | viewVelStreamlinesMaxIterations – Signifies the maximum length of each streamline in the preview. Adjusting the value will provide you with a guide/preview of the velocity field's motion. The Streamline's length is measured in voxels and at the lowest setting, the Streamlines will be no larger than a voxel.

RGB | prv_uvw, prv_uvw_threshold, prv_uvw_threshold2 – Enables the representation of the RGB channel.

Auto Range | prv_autorange – When enabled, automatically adjusts the preview ranges of visible channels for the current frame so that important data is always visible and the preview is always quick.

Bake Streamlines

Bake Streamlines to Splines Button for converting the currently shown Streamline preview (either Velocity Streamlines or Force Streamlines) into native 3ds Max splines. The baked splines can be rendered like any regular 3ds Max spline - through enabling the rendering in the Rendering rollout of the spline settings or via applying a Hair and Fur modifier over the spline.

Auto Bake | autoBakeStreamlineCurvesOnPreviewChange  Enables automatic Streamlines to Splines baking on any change in the Streamlines Preview. While the Auto Bake option is enabled you don't have to press the Bake Streamlines button in order for scene changes to be applied to the splines and changing the timeline frame will update the baked splines. This allows for rendering animations when using the Hair and Fur modifier over the spline.

Slice Preview

Draw a Slice | prv_sect – Only a voxel-thick cross-section of the grid is visible in this mode. This allows for a better view of occluded details and can help when previewing very rich data such as velocity fields.

Along Axis X, Y, Z | prv_sect_axis – Specifies the axis along which the grid is sliced.

Slice Level | prv_sect_lvl – Specifies the offset of the slice from the bottom center of the grid in voxels.

Slice Width | prv_sect_width – Specifies the width of the slice in voxels.