Why is ShapeCast2D colliding, but can also move its full length without collision?

[matt.goode92]

Godot Version

Windows 11, Godot 4.2.1

Question

A RigidBody2D rests on top of a StaticBody2D. A ShapeCast2D is pointed down from the RigidBody. Calling is_colliding() on the ShapeCast2D returns true. Why does get_closest_collision_safe_fraction() return a value of 1?

Here’s the docs entry on get_closest_collision_safe_fraction():

The fraction from the ShapeCast2D 's origin to its target_position (between 0 and 1) of how far the shape can move without triggering a collision.

My understanding of this is that a 1 means that moving the full length of the ShapeCast would trigger no collisions and a 0 means the shape can not move at all without triggering collisions. So if is_colliding() is true, how can get_closest_collision_safe_fraction() be any value above 0? Does get_closest_collision_safe_fraction() ignore any object that the shape is already colliding with at its origin?

Details on the two Bodies:

RigidBody2D is size 128x128 square
StaticBody2D is size 128x128 square
ShapeCast2D is child of the RigidBody2D, centered on it, and size 128x128. Target position is default value (0, 50).

[matt.goode92]

Does get_closest_collision_safe_fraction() ignore any object that the shape is already colliding with at its origin?

In case anyone comes across this question in the future:

I did one more test and may have answered this question with a Yes for myself.

I moved the position of the Shapecast to 1 pixel above the edge of the RigidBody instead of being aligned exactly with it, and the results were immediately as I expected.