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.. _environment-mapping-with-cube-maps:

Environment Mapping with Cube Maps
==================================

Although there are other applications for cube maps, one very common use of
cube maps is as an environment map, similar to
:ref:`sphere mapping <simple-environment-mapping>`. In fact, it works very
much the same as sphere mapping.

Just as with a sphere map, you can have Panda3D generate a cube map for you:



.. code-block:: python
    
    scene = loader.loadModel('bvw-f2004--streetscene/street-scene.egg')
    scene.reparentTo(render)
    scene.setZ(-2)
    base.saveCubeMap('streetscene_cube_#.jpg', size = 256)



:ref:`Click here <sample-cube-map>` to see the six images generated by the
above sample code.

With the cube map saved out as above, you could apply it as an environment map
to the teapot like this:



.. code-block:: python
    
    tex = loader.loadCubeMap('streetscene_cube_#.jpg')
    teapot.setTexGen(TextureStage.getDefault(), TexGenAttrib.MEyeCubeMap)
    teapot.setTexture(tex)



And the result looks very similar to the sphere map:

.. figure:: Cubemap_teapot.jpg
   :alt: The_cube_map_on_a_teapot.

In fact, it looks so similar that one might wonder why we bothered. So far, a
cube map looks pretty similar to a sphere map, except that it consumes six
times the texture memory. Hardly impressive.

But as we mentioned :ref:`earlier <simple-environment-mapping>`, there are two
problems with sphere maps that cube maps can solve. One of these problems is
that the point-of-view is permanently baked into the sphere map. Cube maps
don't necessarily have the same problem. In fact, we can solve it with one
simple variation:



.. code-block:: python
    
    tex = loader.loadCubeMap('streetscene_cube_#.jpg')
    teapot.setTexGen(TextureStage.getDefault(), TexGenAttrib.MWorldCubeMap)
    teapot.setTexture(tex)



By changing ``MEyeCubeMap`` to
``MWorldCubeMap``, we have indicated that
we would like this cube map to vary its point-of-view as the camera moves. Now
the reflected environment will vary according to the direction we are looking
at it, so that it shows what is behind the camera at runtime, instead of
always showing the area behind the camera when the cube map was generated, as
a sphere map must do. In order for this to work properly, you should ensure
that your camera is unrotated (that is,
::
    setHpr(0, 0,
    0)
) when you generate the
cube map initially.

Even with MWorldCubeMap, though, the image is still generated ahead of time,
so the reflection doesn't actually show what is behind the camera at runtime.
It just uses the current camera direction to figure out what part of the
reflection image to show.

However, you can make a cube map that truly does reflect dynamic objects in
the scene, by rendering a :ref:`dynamic cube map <dynamic-cube-maps>`. This
will be discussed in the next section.