Btw, I looked into Stalker DX8 mode, and found that vertex shaders of the distorted polygons uses incoming texture coordinate as integer indices into the shader constant buffer (for vertex 'animation').
So that, texture coordinates are not texture coordinates but integer indices.
This is the equivalent of BLENDINDICES of the fixed function vertex pipeline, that's mentioned in both the DX SDK and the ATI Truform docs that it's not compatible with the technology because indices cannot be interpolated across the triangle in any meaningful way (obviously).
Summarized: in this case TruForm is forced to a shader incompatible with TruForm. It can easily be the same situation with FEAR, vertex blending based on indexed matrices or weights is a very common technology for mesh animation.
But Morrowind... I wish TruForm was implemented in wider amount of games, and that ATI didn't abandoned it.
This technology was advertised in the docs as one that's compatible with traditional meshes containing normal vectors, very easy to use without the need of re-designing existing meshes, unlike with RT-patches, requiring additional information (in fact, the control points).
So, no code and mesh modification is needed, you just enable the feature through the DX API and it automatically/magicallly works.
Well, it's just partially true. Meshes contain shared vertex positions and normals for neighbour triangles, so, for keeping cornered parts of the mesh cornered, it needs to be modified not to use shared vertices for that part.
Or else you get strange things like crates pumped into a stuffed pillow. 😁
So, this technology has it own curse, maybe that's the reason not many games supported it. Or the real time performance. I didn't have the ATI hw back in the day so I myself don't have experience about how well it performed but what I read about it it wasn't stellar.