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Spherical Environment Mapping with OpenGL
ARTICLE NOT FINISHED
Recently I found this great tutorial on spherical environment mapping
which is an easy solution to add some detailed lighting to a visualisation. The
great thing about this technique, is that you can use a simple 2D texture to
define how the lighting and reflection of you model looks. This gives you an
extremelly easy tool for fine tuning the appearence of your objects.
I'm going to describe my implementation here, which is basically the same as
the above linked one; this is just one for my reference. Another great and more
indepth article on how this technique works is described in this description from
1999 by Paul Zimmons.
Describing the environment
There are a couple of common techniques that are used with environment mapping.
You have spherical, cubic and parabolic environment mappings all with their own pros
and cons. Spherical mapping has the great advantage that is just uses one texture
and it's cheap to perform the necessary calculations.
Below you can see how these spherical environment images, also called matcaps,
look like. When you google for matcap, lit sphere, light probe you'll find a lot
of these images. That's how I found the image below ... not knowing who the owner
You can think of this image as a description of how your object will be
shaded. From below it will have red/dark color shades and from the top it
will be bright. When rendering an arbitrary object I created with blender
(with normal mapping) you get something like this:
In your vertex shader we will be calculating the texture coordinate that
we need to use with our matcap texture. The mapping between the texture coordinate
and matcap is described in geat detail in the article of Paul Zimmons.
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