The shortcut hidden beneath the steps
A game character may appear to climb a staircase, but the movement system does not always treat each tread as a separate obstacle. Instead, the stairs can have a simpler collision shape: an invisible sloped surface that lets the character move uphill smoothly. This simplified shape is called a collision proxy—the version of the world used to calculate movement and contact, which need not match every visible detail.
That shortcut makes movement easier to control. A character crossing dozens of small edges would otherwise need repeated decisions about whether a foot has reached the next step, whether the body should rise, and whether a collision should stop forward motion. A continuous slope avoids many of those abrupt transitions.
Why the feet give the trick away
The character’s visible animation and the surface that governs movement are related but not identical. The movement system can carry the character smoothly up the hidden slope while the animation continues to swing the legs as if they were stepping from tread to tread. If the model’s feet do not line up with the actual stair edges, they can seem to float above a step or dip into it.
Sharp corners make the mismatch easier to notice. There, the character may shift suddenly as the movement system resolves contact with the sloped surface, producing a brief jitter. The effect is especially visible when the camera is close or the character moves slowly, because the eye has more time to compare each foot with each tread.
A tradeoff between reliable movement and precise contact
Using a ramp-like surface can keep ordinary movement predictable, but it sacrifices exact foot placement. A game can reduce the visual mismatch with animations or more detailed movement logic, yet those additions require extra work and can create their own edge cases. The hovering foot is therefore a small, visible clue that the stairs on screen and the stairs the character is actually walking on may be two different shapes.
