Unfortunately Epic has made it impossible for me to support UE 4.5… They removed custom nonrectangular hit-testing completely, meaning I can’t integrate at all with Slate in 2D… From the source:
/**
* DEPRECATED: This function caused a lot of confusion, and we found that all known uses of it were unnecessary.
* We will provide a less confusing API for supporting non-rectangular hittesting and pixel-perfect hit testing.
*/
DEPRECATED(4.5, "OnHitTest is no longer called. It will be replaced by more robust hit testing logic in the near future.")
At least it sounds like there will be something coming in the near future to replace it (that will hopefully support Radiant). Have posted on the Answerhub to get assistance?