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Krakatoa MX Atmospheric Effect

 Available in Krakatoa MX v2.0.0 and higher

Overview

The Krakatoa Atmospheric effect is a ray-marcher implemented within the 3ds Max atmospheric sub-system. As such, it will work with any renderer that supports the native atmospheric effects of 3ds Max, including Scanline, V-Ray, finalRender and Brazil r/s.

The Krakatoa Atmospheric effect produces a render output very similar to the Voxel mode of Krakatoa, but it can be integrated directly into geometry renderers including the ability to cast and receive shadows on and from geometry objects and other atmospherics and to interact with raytraced reflections and refractions without intermediate steps, multiple render passes or compositing tricks.

The Krakatoa Atmospheric effect requires more memory than the Krakatoa Voxel mode because all voxels have to be allocated at once.

User Interface

Add Particle Objects... button

This button opens a Select By Name dialog and lets you add one or more PRT objects from the scene to the Krakatoa Atmospheric effect. Only objects listed in the Particle Objects list box will be rendered.

Remove Particle Objects button

Select the PRT objects you want to remove from the Krakatoa Atmospheric effect and press this button.

Voxel Length spinner

This value controls the size of the voxels in world units and thus defines the resolution of the effect. Larger values will produce blurrier results but will render faster and use less memory. Smaller values will increase the detail but also cost more in terms of time and memory.

Max. Step and Min.Step spinners

These two values control the ray marching step through the voxel grid. They are both expressed as factors of the Voxel Length, in other words a value of 1.0 means "same as Voxel Length", a value of 0.5 means "Half Voxel Length" and 2.0 means "Double the Voxel Lenght".

The default values are 1.0 for both - in that case, the ray marcher will step through the volume at intervals equal to the Voxel Length.

When the Max. Step is higher than the Min. Step, adaptive sampling will be performed. The ray will march with the Max.Step first and compare the Density values at the previous and new sample. If the two values are different, the step will be reduced by half and a new sample will be taken. The process will be repeated until the previous and the new sample have the same value or the Min.Step has been reached. This means that when marching through a volume with isotropic density, the Max. Step will be used and each sample will have about the same Density value as the previous one. When the ray marching reaches a portion of the volume with changing Density, the step will be automatically reduced down to the Min.Step to capture all the detail.

The two spinners are connected in such a way that you cannot set the Min.Step higher than the Max.Step - the two will "bump" and stick to the same value, effectively disabling adaptive sampling.

Shading Controls

The two options are equivalent to the >Use Emission and >Use Absorptions controls found in the Krakatoa Main Controls rollout. When disabled, only the Density and Color channels will be used. When enabled, Emission and/or Absorption will also be taken into account.

Lighting and Camera Density and Emission Scale Controls

The spinners in this group of controls are equivalent to the Lighting Pass Density, Final Pass Density and Emission Strength controls in the Krakatoa Main Controls rollout. Since there are no separate passes for Lighting and Drawing, the term "Camera Pass" is used for the rendering controls.

You can use these values to define separate Density for the lighting rays and for the camera rays, and to control the Emission channel contribution to the final rendering.

 

See Also