POV-Ray : Documentation : Some media concepts
  POV-Ray 3.6 Documentation Online View Types of media Simple media examples Some media concepts

Media can be global to the whole universe, or it can be contained by an object. In the latter case the media is defined in the interior block of the object definition.

For an object to be able to contain media (or to allow media from other objects or the global media inside itself) it has to be defined as hollow (a common mistake is to forget adding this keyword). If an object with no media should not allow media inside itself (eg. a solid glass ball), then hollow should not be defined for that object.

If media is defined in the interior of an object or as a global media it will have a constant density throughout the object/universe. However, a density pattern can be specified for non-uniform media. Also all kinds of transformations can be applied to the media. This is specially useful for various effects (such as smoke with certain shape). Types of media Simple media examples

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