Casting Shadows on Geometry

Introduction

Krakatoa is a pure volumetric point renderer.

Scene geometry can be rendered by Krakatoa either as a cloud of particles using the geometry vertices, or as a matte object occluding the particles. While Matte Objects can cast shadows on particles (as long as the shadow casting is turned on in the Light source), the shadows cast by Krakatoa particles onto matte objects cannot be represented directly.

Thankfully, Krakatoa provides an option to save attenuation maps to disk to be used as projector maps to attenuate the lighting of the same Light sources in a different renderer like Default Scanline, mental ray, Brazil, V-Ray etc.

Workflow

Here is the workflow to get Krakatoa-rendered particles to cast shadows on scene geometry.

• Create particles, add shadow-casting light(s), add matte objects
• Enable Attenuation Map Saving
• Set image output path and render - At this point, you should have the Krakatoa frames plus a sub-folder \Shadows containing the attenuation maps of all shadow-casting lights.
• Open the Shadows Utility.
• CHANGE THE RENDERER! (to Scanline, Brazil, VRay, Mental Ray...)
  • You can either select a renderer class to assign a new renderer (which is equivalent to using the Change Renderer controls in the Render Scene Dialog)
  • Or you can load an existing 3ds Max Render Preset.

 NOTE: It is strongly recommended to use the options for changing renderers in the Shadows utility - 
 when using it, the current Krakatoa settings will be saved to a Render Preset and can be restored later.

• Pick the path where the shadows were saved to. By default, the utility will scan the Output Path currently set in the Render Scene Dialog so it should detect the shadows folder automatically in most cases.
• Press the button - this should add a projection map to each light in the scene based on its name, matching the file names in the Shadows directory
• Set a new save path in the Render Scene Dialog.
• Render in your renderer of choice (but not Krakatoa!).

Result: You should get frames where there are no Krakatoa particles in the scene but the geometry renders AND the lights are projecting the attenuation maps onto the scene. The combination of the Shadow Map shadow casting and the attenuation map in the Projector slot should produce a scene that has shadows cast from (non-visible) Krakatoa Particles onto geometry and from geometry onto geometry.

Now load both frames in some Post application and composite the particles on top of the geometry rendering - the particles will appear to be casting shadows onto the rest of the scene.

You can press the Restore Krakatoa Renderer button if you want to switch the scene back from the current renderer. (we save/load a Max Render Preset to do this, you can save two versions of the scene if you prefer to have Krakatoa and your other Renderer separated).

See Shadows On Geometry Utility for details on the Utility used to perform these steps.