Oculus compatible with dx9 ??

Here's an example of a DXD9 warp shader from Vireio:

https://github.com/cybereality/Perception/blob/master/Release/Perception/fx/OculusRift.fx

I just added chromatic aberration correction to it the other day. Someone can probably help out and make it more efficient, I had never written any shaders before and was modifying it without any compiler tools so I couldn't tell the reasons it was failing (I think each shader model has limited registers and instruction count).

The post process shaders do nothing more than a texture lookup controlled by a relatively simple function (could also be done by a second indirection texture), maybe three lookups if the chromatic aberration gets corrected. So you can implement this on *any* 3D API that supports basic fragment shaders (DX9, GL 2.0, GL ES 2.0 etc.) - probably even DirectX 8 shaders...

... and shaders aren't really necessary anyway, so you could even use OpenGL ES 1.x, simple unextended OpenGL 1.2 or DirectX 7 if you liked. Just generate a tesselated quad with the pre-distortion function applied to either texture coordinates or vertex positions, and use that to show the textures with the two views instead of simple quad(s).

valve's method, iirc, is to precompute the distortion and chromatic abherations onto a texture. There are loads of methods to do the barrel distortion shader.