MayaMan Tutorial: Soft Shadows

This tutorial explains how to use shadow maps from other lights in order to make the shadows from a particular light appear "soft". An example scene with a reference image can be found in the MayaMan Example Scenes Pack which can be downloaded here

Note, this tutorial assumes a certain level of familiarity with 3D Maya, in particular the ability to create objects, animations and materials i.e. you should be able to build simple Maya scenes.

Before commencing, ensure your RenderMan renderers are correctly installed, and that you have performed a successful MayaMan installation.
Start off by creating a ground plane and put a cylinder on the plane. Scale the cylinder up in the y-direction and down in the x/z-directions
Create a spotlight that points towards the cylinder. Enable depth map shadows for the light. (you may want to reduce the resolution of the shadow map to save render time)
Do a MayaMan preview render. You should get exactly what you expect, ie a cylinder with a normal (but noisy) shadow.
Now, add a MayaMan Light Attributes node to the light, and browse to the Soft hadows section using the Attribute Editor. Click "enable soft shadows", and set "Shape" to be "Line"
Click on the small checker box next to SoftShadower_0. This will create a new light. Orient that light so that it is pointing towards the cone from almost the same direction, but a bit to the left of the first light. All SoftShadower_lights's frustrums must contain all the objects that will cast soft shadows.
Add a third light to the right of the first light, so that you now have three lights on an almost straigth line.
Do a MayaMan preview. You will most probably get a very ugly "peppery" pattern on the ground plane instead of the nice, soft shadows you were expecting. Needless to say, there are a few parameters that need tweaking.
In the MayaMan Light Attributes panel, increase the number of samples to 16 or more and turn on gaussian filter.
In the MayaMan Light Attributes panel, in the Soft Shadows section, increase the Gap Bias to 0.2.
In the Attribute Editor for the Maya light, increase the dmap bias for each light to 0.2.
Do another preview. You should now have a rather soft shadow, but it may still be a bit noisy. Increasing the samples even more will get rid of the remaining noise, but it will cost in render speed.
Last but not least: You will need a bit more background knowledge in order to make the most out of Soft Shadows in Renderman. This tutorial has shown you how to setup a soft shadow scene using MayaMan, but you still benefit from reading up on the renderman application notes on soft shadows (appnote #26). A thorough knowledge of what all parameters mean is essential in order to know how to tweak them.
Done. If you had any problems/difficulties completing this tutorial, or have suggestions on how to make the tutorial better, or even suggestions for other tutorials, please email support@al.com.au

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