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  LibGDX Box2D Raycast problem  (Read 1243 times)
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Offline pploco1996

Junior Devvie

Medals: 2
Exp: 1 year

« Posted 2014-05-16 03:30:20 »

Hi, JGO.

I have a problem with Raycastcast Callback: When I return the fraction it does give me the closest hit point but not the closest fixture.

I need the closest fixture because I'm using rays as enemy "eyesight".

Hope you can help me.

Thanks in advance.
Offline ewg

Senior Devvie

Medals: 10

Java games rock!

« Reply #1 - Posted 2014-05-16 05:49:13 »

You need to create a class that implements the interface com.badlogic.gdx.physics.box2d.RayCastCallback so that your class has a method:
float reportRayFixture(Fixture fixture, Vector2 point, Vector2 normal, float fraction)

Then call this method:
 World.rayCast(RayCastCallback callback, Vector2 point1, Vector2 point2)
and pass in an instance of your class as the first parameter.

Your implementation of the reportRayFixture method will then be called by Box2d.  Your implementation should save the Fixture that is passed into it, this is how you get the fixture data.
Offline pploco1996

Junior Devvie

Medals: 2
Exp: 1 year

« Reply #2 - Posted 2014-05-16 14:19:36 »

Thanks but that's not the answer I'm looking for.

I already know how to use Raycast Callback. What I need is to know how to get the fixture that is closer to the origin of the ray.
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Offline ewg

Senior Devvie

Medals: 10

Java games rock!

« Reply #3 - Posted 2014-05-16 16:07:53 »

If you always return 1 in your implementation of the reportRayFixture method then box2d will call your method once per intersection.  Your implementation must compare and save the fraction value and fixture that are passed in if the fraction value is the smallest one that it has seen.

A problem you may come across is that box2d will not report any intersections with fixtures that the start point of the ray was already inside.  If you do want these fixtures you have the option of 1) calling raycast again with the order of the input points reversed so that the raycast is backwards and then finding the fixture returned with the highest fraction instead of the lowest fraction and then do the math to determine if it is closer to the real start point than the closest fixture from the ray cast call with the points in the correct order OR 2) use QueryAABB on the start point to determine which fixtures it is inside.
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