Possible Duplicate:
Detect Open Space in Farseer
How do I detect ledges?

I'm making a 2D platformer with Box2D. The player needs to be able to grab onto a ledge and pull him/herself up.

Right now I have a sensor that extends in every direction from the upper half of the player's body.

The logic seems simple enough: if there are tiles inside the sensor and empty space above them, then it's a ledge and the game should act accordingly. The problem is that I can't figure out how to implement that logic with Box2D.

Anyone have any ideas?

  • \$\begingroup\$ I've answered this myself in another question which this would be a duplicate of. \$\endgroup\$ Oct 2, 2012 at 23:12

2 Answers 2


What I needed to do was have two sensors. One extending outward of the upper half of the body, one with the exact same dimensions right above it.

If the top sensor isn't colliding with anything, and the bottom sensor is, it's a ledge.


Since no one has answered, check here. It should be the same



  • 3
    \$\begingroup\$ Those links only explain how to use sensors. I already understood that. I had trouble figuring out if what the sensor was colliding with was, in fact, a ledge. \$\endgroup\$ Oct 2, 2012 at 19:42
  • \$\begingroup\$ Hi Anonymous, and welcome to GDSE! Answers that are barely more than links are generally less than optimal, since the moment that forum topic is deleted or otherwise 404s, your answer becomes a lot less useful. It's better to actually provide an explanation in your answer. In this case, though, there's also nothing directly about ledge detection! I'm downvoting this answer. \$\endgroup\$ Oct 19, 2012 at 0:34

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