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PhotoRealistic RenderMan^® Extension

Supplemental documentation for the shadow map generation feature of the "prman" render package.

Shadows

Automatic shadow generation is supported for the standard light source shaders and new shadow lights can be defined. However, in order to get the best results, image specific "tweaking" will still have to be performed by the user.

Figure 1 shows 3 gprims rendered with shadows. Figure 2 shows the same scene, but **`casts-shadows`** is used to demonstrate the 3 available behaviors described below; specifically, the sphere does not cast a shadow and the torus casts a shadow "only."

fig.1	fig.2

Shadow Lights

Shadow lights is a term describing the light source shaders that AL can automatically produce shadows for. Support is provided for a limited (but extendable) set of shadow lights.

distantlight
pointlight
spotlight

The light-shadows gop is used to specify which light sources produce shadows. (Light sources don't produce shadows by default.)

   ...
   (light "distantlight")   ;; doesn't cast shadows
   (light-shadows #t)
   (light "distantlight")   ;; does cast shadows
   ...

Note that for the distant light which casts shadows, the same shader "distantlight" is specified. The only difference is that the distant light which casts shadows takes additional parameters necessary for various aspects of shadow map generation and use.

All shadow lights support the following parameters when producing shadows:

standard shadow light parameters
(light-shadows = #t only)

shadow-map-res	real	256	shadow map resolution
shadow-map-dir	string	current directory	shadow map directory
options	list of uneval'd options	see below	light-source specific shadow map rendering options

distantlight

(light "distantlight" paramlist)

name	type	default	description
intensity	real	1.0	intensity
lightcolor	vec3	#<1 1 1>	color
from	vec3	#<0 0 0>	position
to	vec3	#<0 0 1>	center of interest

light-shadows = #t only

shadowname string "shadowdistant~s" shadow map filename
samples real 16 sampling resolution
width real 1 sampling filter width

pointlight

(light "pointlight" paramlist)

name	type	default	description
intensity	real	1.0	intensity
lightcolor	vec3	#<1 1 1>	color
from	vec3	#<0 0 0>	position

light-shadows = #t only

sfpx string "shadowpoint~spx" shadow map filename +X axis
sfnx string "shadowpoint~snx" shadow map filename -X axis
sfpy string "shadowpoint~spy" shadow map filename +Y axis
sfny string "shadowpoint~sny" shadow map filename -Y axis
sfpz string "shadowpoint~spz" shadow map filename +Z axis
sfnz string "shadowpoint~snz" shadow map filename -Z axis
samples real 16 sampling resolution
width real 1 sampling filter width

spotlight

(light "spotlight" paramlist)

name	type	default	description
intensity	real	1.0	intensity
lightcolor	vec3	#<1 1 1>	color
from	vec3	#<0 0 0>	position
to	vec3	#<0 0 1>	center of interest
coneangle	real	(radians 30)	cone angle
conedeltaangle	real	(radians 5)	cone fuzziness angle
beamdistribution	real	2	drop off

light-shadows = #t only

shadowname string "shadowspot~s" shadow map filename
samples real 16 sampling resolution
width real 1 sampling filter width

How Objects Cast Shadows

You can specify how gprims cast shadows using the casts-shadows gop.

(casts-shadows #t)

Subsequent gprims will cast shadows. (The default.)

(casts-shadows #f)

Subsequent gprims will not cast shadows.

(casts-shadows "only")

Subsequent gprims will only cast shadows. That is, their shadows will be visible, but the geometry itself will not.

Shadow Map Names

Note that the default shadow map filenames all contain "~s". The "~s" is replaced by an integer index which is unique for each map. You may exclude the "~s" as long as the shadow map filename is unique from other shadow lights.

Shadow Map Tweaking

The things that need to be tweaked:

shadow map resolution (shadow light parameter "shadow-map-res"); bigger maps take longer to render but give better results
shadow map samples (shadow light parameter "samples"); more samples yield better results but take longer
shadow map width (shadow light parameter "width"); amount of blurriness in shadow maps -- used to soften edges
shadow bias (global rendering option, see attributes/options); you'll get spots (surface acne) if too small, and detached shadows if too large

Adding New Shadow Lights

Coming Soon!

Shadow Map Rendering Options

The default value for "shadow-map-options" is

     '((ri-pixel-samples 1 1)
       (ri-pixel-filter "box" 1 1)
       (ri-hider "hidden" 'jitter 0))

Note: This single option specifies all rendering options for the generation of shadow maps. (Its use may be improved in the future.) You generally will want to retain the settings for the shadow map options show above. Therefore, if you need to specify an additional rendering option for the shadow map (e.g. "zthreshold"), you should include that option and those shown above. For example,

(render 
	...

 	'shadow-map-options
	'((ri-pixel-samples 1 1)
	  (ri-pixel-filter "box" 1 1)
	  (ri-hider "hidden" 'jitter 0)
	  (ri-option "limits" 'zthreshold '(0 0 0))
	  )

	...
	)

Last updated: 4/15/96 / Steve May ( smay@cgrg.ohio-state.edu )

Any comments or suggestions appreciated.

shadowname	string	"shadowdistant~s"	shadow map filename
samples	real	16	sampling resolution
width	real	1	sampling filter width

sfpx	string	"shadowpoint~spx"	shadow map filename +X axis
sfnx	string	"shadowpoint~snx"	shadow map filename -X axis
sfpy	string	"shadowpoint~spy"	shadow map filename +Y axis
sfny	string	"shadowpoint~sny"	shadow map filename -Y axis
sfpz	string	"shadowpoint~spz"	shadow map filename +Z axis
sfnz	string	"shadowpoint~snz"	shadow map filename -Z axis
samples	real	16	sampling resolution
width	real	1	sampling filter width

shadowname	string	"shadowspot~s"	shadow map filename
samples	real	16	sampling resolution
width	real	1	sampling filter width