How do I perform a circular/rotational/spin blur on an image - using DirectX9.0 and HLSL?
You will need to work in Polar Coordinates. In order to convert Cartesian Coordinates into Polar you use the following:
This will get the coordinates around
Once you have the polar coordinates you can use a typical multi-tap blur to perform the blur.
A blur just uses temporal coherence. It doesn't really matter what technology you're using to implement it, so long as you know how to do alpha, you're all good to go.
Of course, you needn't just have one