The media
statement is used to specify particulate matter suspended in a medium such air or water. It can be used to specify smoke, haze, fog, gas, fire, dust etc. Previous versions of POV-Ray had two incompatible systems for generating such effects. One was halo
for effects enclosed in a transparent or semi-transparent object. The other was atmosphere
for effects that permeated the entire scene. This duplication of systems was complex and unnecessary. Both halo
and atmosphere
have been eliminated. See "Why are Interior and Media Necessary?" for further details on this change. See "Object Media" for details on how to use media
with objects. See "Atmospheric Media" for details on using media
for atmospheric effects outside of objects. This section and the sub-sections which follow explains the details of the various media
options which are useful for either object media or atmospheric media.
Media works by sampling the density of particles at some specified number of points along the ray's path. Sub-samples are also taken until the results reach a specified confidence level. When used in an object's interior
statement, sampling only occurs inside the object. When used for atmospheric media, the samples run from the camera location until the ray strikes an object. Therefore for localized effects, it is best to use an enclosing object even though the density pattern might only produce results in a small area whether the media was enclosed or not.
The complete syntax for a media
statement is as follows:
media {
[MEDIA_IDENTIFIER] [MEDIA_ITEMS...] }
intervals
Number | samples
Min,
Max |
confidence
Value | variance
Value | ratio
Value |
absorption
COLOR | emission
COLOR |
scattering {
Type,
COLOR [ eccentricity
Value ] [ extinction
Value ] }
|
density {
[DENSITY_IDENTIFIER] [PATTERN_TYPE] [DENSITY_MODIFIER...] }
|
color_map{
COLOR_MAP_BODY }
| colour_map{
COLOR_MAP_BODY }
|
density_map{
DENSITY_MAP_BODY }
If a media identifier is specified, it must be the first item. All other media items may be specified in any order. All are optional. You may have multiple density
statements in a single media
statement. See "_Ref420163912" for details. Transformations apply only the density
statements which have been already specified. Any density
after a transformation is not affected. If the media
has no density
statements and none was specified in any media identifier, then the transformation has no effect. All other media items except for density
and transformations override default values or any previously set values for this media
statement.
Note that some media effects depend upon light sources. However the participation of a light source depends upon the media_interaction
and media_attenuation
keywords. See "Atmospheric Media Interaction" and "Atmospheric Attenuation" for details.
Note a strange design side-effect was discovered during testing and it was too difficult to fix. If the enclosing object uses transmit
rather than filter
for transparency, then the media
casts no shadows. For example:
object{MyObject pigment{rgbt 1.0} interior{media{MyMedia}}} //no shadows object{MyObject pigment{rgbf 1.0} interior{media{MyMedia}}} //shadows