Raycast Bindings about box2d.js HOT 11 CLOSED

Seems like I've got it working too! Thanks a lot!

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After a day of messing around with this, I was finally able to successfully build Box2D with the b2RayCastInput and b2RayCastOutput bindings. As a web developer it's quite humbling to see the complexity that goes into something like this. I followed the suggestions in Issue #3 and added simple constructors to the missing structures. The method I was after was b2Fixture.RayCast and not b2World.RayCast which led to more confusion with the customizeVTable.

Anyway, I cleared it up and it's running great.

For anyone interested this is what I changed in b2Collision.h

/// Ray-cast input data. The ray extends from p1 to p1 + maxFraction * (p2 - p1).
struct b2RayCastInput
{
    b2RayCastInput() {}
    b2Vec2 p1;
    b2Vec2 p2;
    float32 maxFraction;
};

/// Ray-cast output data. The ray hits at p1 + fraction * (p2 - p1), where p1 and p2
/// come from b2RayCastInput.
struct b2RayCastOutput
{
    b2RayCastOutput() {}
    b2Vec2 normal;
    float32 fraction;
};

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Without compiling myself, how can I get basic raycasts to work?

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Even when compiling yourself, do you use a JSQueryCallback to use raycasts? @shannon -- if you're still looking at this issue, just wondering what JS code interfaces with your changes. Thanks!

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@cwindolf It's been a really long time but looking over my code from back then it's something like this:

var rayCastInput = new Box2D.b2RayCastInput();
var rayCastOutput =  new Box2D.b2RayCastOutput();

function raycast(b2Fixture, p1, p2, maxFraction){
  rayCastInput.set_p1(p1);
  rayCastInput.set_p2(p2);
  rayCastInput.set_maxFraction(maxFraction);
  if(b2Fixture.RayCast(rayCastOutput, rayCastInput)){
    return {
      normal: rayCastOutput.get_normal(),
      fraction: rayCastOutput.get_fraction()
    }
  }
  return false;
}

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Whoa, fast reply, was barely expecting one! Looks promising, thanks very much @shannon!

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While looking fix history and change logs, seems like b2RayCastInput/b2RayCastOutput has been already added to b2Collision.h. But still, I'm getting exception while trying to create new instance of those objects: "cannot construct a b2RayCastInput, no constructor in IDL". Tried booth builded versions 2.3.1_min.js/2.2.1_min.js

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@IljaK I'm having the same issue. I tried doing raycasts through the JSQueryCallback but they don't work for me. Any leads on how to fix this?

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I did get this to work eventually. The build I'm using doesn't take JSQueryCallback, b2RayCastInput or b2RayCastOutput. It takes a JSRayCastCallback and two points. The JSRayCastCallback must then implement the ReportFixture function, which takes a fixture, a point, a normal and a fraction in that order.

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Could you paste some code example?

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Sure. In this code, box2d is my instantiated box2D. This code is not finished at all, but it logs the correct fraction of the ray because ReportFixture is called.

    const _callback = new box2d.JSRayCastCallback();

    const configureCallback = () => {
        _callback.ReportFixture = function(fixture, point, normal, fraction) {
            const f = box2d.wrapPointer(fixture, box2d.b2Fixture);

            _callback.m_fixture = fixture;

            if (f)
                console.log(fraction);

            return fraction;
        };
    };

    /**
     * Get the length of the ray.
     * @returns {Number} The portion of the ray that could be cast in the range [0, 1].
     */
    this.getLength = () => {
        let from = body._getBody().GetWorldPoint(new box2d.b2Vec2(x, y));

        world.RayCast(
            _callback,
            new box2d.b2Vec2(from.get_x(), from.get_y()),
            new box2d.b2Vec2(from.get_x() + ray.x, from.get_y() + ray.y));

        return 0.5;
    };

    configureCallback();

from box2d.js.