Introduction - Creating a Soft Shadow

Soft shadows can simulate a diffuse light source. To accomplish the effect of area lights, soft shadows become "softer" they more they recede from the base of an object. MTOR can be used to control how soft and how detailed the shadow is.

Soft shadows take longer to generate than ordinary shadows for two reasons. To create soft shadows multiple shadow maps are generated, between four and eight, and then these maps must be averaged together. Soft shadows provide an excellent, but expensive, solution for cases where shading with area lights is desired. 

For more information about soft shadows see Application Note #26.

1 - Import Map Generator

(Use scene ladder2.ma, or use the completed scene from the last lesson, and turn the shadows off.)

In the last tutorial, the shadow map was generated with the light shader. In this  tutorial, another method will be used to generate shadow maps, through the use of a Map Generator.

Map generators can be attached in addition to any other  a types of shaders. They are used to generate  arbitrary maps from lights, objects, cameras, and coordinate systems. These maps can then be referenced by other shaders. 

In this example, we'll use a map generator that creates maps for soft shadows. To create a map generator:

File-> Create Appearance-> MapGen-> Soft Shadow

Your palette should look now contain a Soft Shadow Map Generator, like the one on the right.

The palette with a Map Generator

2 - Setting up the Map Generator

First, attach the Soft Shadow map generator to the key light.

Now open the map generator in the appearance editor, by double-clicking on its icon in the palette.

To enable soft shadows do the following:

1) Make sure Frequency is set to "Every Frame"

2) Open the Soft Shadow Controls, (by double-clicking on the multi-colored box) and set Softsize to "4," and this will control how much the shadow blurs as it recedes from the base of an object.

(There's more info about Map Generators, in the Shader Concepts section.)

1 - Setting up the  light shader

Make sure the keyLight shader is attached to the Maya key light. (Note: Both the light shader and the map generator can (and should) be attached to the Maya light at the same time.)

Open the keyLight shader in the appearance editor. To generate soft shadows, three things must be done:
1) The light shader's shadowname parameter must be set to refer to the soft shadow maps. To do this click on the shadowname's texture button (the blue, yellow, purple, and green button) and a pull-down menu will appear, select: Refer to-> softshadow
This text will appear in the field:
[shdmap $OBJNAME soft]
 
"$OBJNAME" tells the shader to use the soft shadow maps that have named after the object the light shader is attached to, which, in this case, are the maps generated by our map generator.

2) Soft Shadows must be enabled, by clicking on the box.

3) The Soft Shadow Size setting in the keyLight should match the softsize parameter in the map generator.

Notice that since the light shader will be using the shadow maps created by the map generator, the light shader itself doesn't need to create a shadow map. Its Frequency setting can be set to "Never."

4 - Render the soft shadows

RenderMan-> Render
Soft shadows should appear.

The job will take a little longer to render with soft shadows. To see the job progress, open up the Alfred Job Window for this render (like we did in tutorial 2). In the job window there should be four shadow maps generating. In the image on the right, we can see that the first two shadow maps are complete, and the third map is halfway done. 

When the final images renders, the shadows should falloff, like the shadows in the image on the right.

Soft Shadow Notes - Tips and Tricks

Tips and tricks for working with soft shadows.

Note A - Viewing the Soft Shadow Maps

Now try taking a look at the shadow maps using the techniques from tutorial 2.

In the shadow maps on the right it is more obvious how the camera actually pivots to generate multiple shadow maps.

Important: Note that when setting up soft shadows in your own scenes, make sure that the light's manipulator is near the base of the object(s) casting soft shadows. The light manipulator serves as the pivot point for the soft shadow generation. So when the light manipulator is far away from the base of the objects, the pivot will be incorrect and the shadows behave poorly, like not appearing. The moral is to keep the light manipulator near the base of shadow casting objects.

(To show a light manipulator, select the Maya light and press "T".)