As we only have AABB collision boxes, how do we handle slanted platforms in a 2D platformer, such that the player can walk up a hill?
I can only think of having a property on the tile that declares it's angle and when a player collides with it, setting the player's position according to a function of the angle and the x position within it.
How have other's handled it?
The sdk sprite collision system just isn't build for that kind of thing really. It starts getting into the realm of needing to build your own physics solution. There are a couple of threads (similar to the one you made a month ago asking the same question) that have a few ways people have tried to jam slopes into the sdk collision system.
This one is pretty good if all you need is the position on the slope.