Rotate a texture depending on depthFade gradient direction?

I render a texture on the depthFade gradient and would like to rotate it corresponding to the gradient’s direction (see image)

My idea was to calculate a 2D Vector (XY) representing the depthFade direction from top view.
Then get the angle between that one and the x-axis and rotate my texture by that.

Sadly i have no clue how to get the 2D Vector respresenting the gradient’s direction, but maybe someone of you got a tip for me OR has a different solution :slight_smile: