One of today's main Gamasutra feature is an extract, by Alan Watt and Fabio Policarpo, from the book Advanced Game Development with Programmable Graphics Hardware, particularly focusing on a section dealing with 'Shadow Techniques for Relief Texture Mapped Objects'.
As Watt and Policarpo explain in this extract:
"Integrating shadows to the relief map objects is an important feature in fully integrating the effect into a game scenario. The corrected depth option, which ensures that the depth values stored in Z-buffer include the displaced depth from the relief map, makes it possible to implement correct shadow effects for such objects. We consider the use of stencil shadows and shadow maps in this context. We can implement three types of shadows: shadows from relief object to the world, from the world to relief object and from relief object to itself (self-shadows).
Let us first consider what can be achieved using stencil volume shadows. When generating the shadow volumes, we can only use the polygons from the original mesh to generate the volume. This means that the shadows from relief objects to the world will not show the displaced geometry of the relief texture, but will reflect the shape of the original triangle mesh without the displaced pixels.
However, as we have the corrected depth stored in Z-buffer when rendering the lighting pass we can have shadows volumes from the world projected onto the relief objects correctly, and they will follow the displaced geometry properly. Self-shadows (relief object to itself) are not possible with stencil shadows."
You can now read the full Gamasutra feature
on the subject (no registration required, please feel free to link to the article from external websites).