In image editing software, you often have the ability to do a directional blur where you can choose and angle and a magnitude of a blur.
How does this actually work in practice with Gaussian blurring?
I could see possibly doing something like making the blur go across the axis specified by the angle and use some sort of texture sampling to find the appropriate sample (bilinear or bicubic sampling), but that seems like it probably isn't correct.
How does directional blurring usually work?
I would say this is in fact motion blur, but I'm asking specifically about the blurring portion, not the whole set up for motion blur within a renderer.
For instance before and after: