Using box2d to detect collisions, but ignore the forces

Question

I'm using libgdx and box2d to detect collisions, but I want some collision to be detected but the forces not to play out.

Eg, I want to detect when the character collides with a coin but don't want the coin to affect the player's movements.

Is this even possible using box2d? If so, how can I go about doing it?

Answer 1

I'm not sure what you want do, but if I understand what you want to do, you can create a sensor fixture type, this pseudo example:

FixtureDef fd1 = new FixtureDef();
//fd1.friction = 0.5f;

PolygonShape pSTest = new PolygonShape();

//size you want for example:
pSTest.setAsBox(4f / PIXEL_POR_METRO, 
                1f / PIXEL_POR_METRO, 
                new Vector2(22f / PIXEL_POR_METRO, -1f / PIXEL_POR_METRO),
                0f);

fd1.shape = pSTest;
fd1.isSensor = true;

yourBody.createFixture(fd1).setUserData("yourId");

looks ContactListener interface, for example preSolve

note that sensor, this is not called for sensors.

info

setAsBox(float hx, float hy, Vector2 center, float angle)

Parameters:
hx the half-width.
hy the half-height.
center the center of the box in local coordinates.
angle the rotation in radians of the box in local coordinates.