Environment Map

Above: Image uses a picture in screen coordinates as a background.

Below: Image shows spherical mapping coordinates applied using a checker map.

Texture coordinates lock a map to geometry. Environment coordinates, on the other hand, lock a map to the world. If you move the object, the map remains in place. If you move the view (or camera), the map changes. This type of mapping system is used with reflection, refraction, and environment maps.

There are four types of environment coordinates:

The first three are the same as those used by the UVW Map modifier. If you imagine a sphere, infinite in size, surrounding your scene and mapped with spherical mapping coordinates, you can visualize the effect you get with spherical environment mapping. Shrink-wrap wraps the map around a giant sphere, leaving only one singularity. Cylindrical is like a giant cylinder.

The Screen system maps the image directly to the view, with no distortion. It's similar to planar, in that it's like a giant backdrop hung in the scene. Unlike the other environment mapping methods, Screen is locked to the view. When you move the camera, the map moves with it. Therefore, you can only use it for still renderings, or animations in which the camera doesn't move.

To use a bitmap with any environmental mapping system other than Screen, you need a high-resolution map because of the size of the virtual sphere, or cylinder.

An environment map is not assigned in the Material Editor, because it's not applied to the geometry of an object, but rather to the scene itself. Environment maps appear in the background, as seen from the camera or perspective view.

When you assign a map to the environment, it's the same as if you'd assigned a mapped material to an object in your scene. To edit or adjust the assigned map, you need to place it in one of the sample slots in the Material Editor. You can do that in one of two ways:

Note: To control whether or not the renderer uses the environment map's alpha channel in creating the alpha for the rendered image, choose Customize > Preferences > Rendering ,and then turn on Use Environment Alpha in the Background Antialiasing group. If Use Environment Alpha is turned off (the default) the background receives an alpha of 0 (completely transparent). If Use Environment Alpha is turned on, the alpha of the resulting image is a combination of the scene and background image's alpha. Also, when writing TGA files with Pre-Multiplied Alpha set to off, turning on Use Environment Alpha prevents incorrect results. Note that only background images with alpha channels or black backgrounds are supported when compositing in other programs such as Photoshop.