Inverted gravity problem

Discuss issues specific the Java port of Box2D
Posts: 1
Joined: Wed Apr 12, 2017 3:33 am

Inverted gravity problem

Postby jdleung » Wed Apr 12, 2017 3:36 am

I'm using jbox2d in Android, I found all the examples on the web have a negative gravity(-9.8), but in my version, I have to set it to a positive value so that body can be pulled down by gravity, a negative value makes it goes upward.and I have to set it bigger than others.

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Vec2 gravity = new Vec2(0, 50f);

Is there any problem with my download version?


Posts: 1
Joined: Sun Apr 23, 2017 7:44 am

Re: Inverted gravity problem

Postby JeneaV » Sun Apr 23, 2017 7:57 am

Looks like something is implemented wrong.

Look at this picture below. On the left side you can see that Y axis of box2d world actually is pointing up and the gravity applied on every object have to be negative so

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body.applyForceToCenter(new Vector2(0, -9.8f), false);
will push world objects down.
On the right side you can see that so called processing world (you can think of it as a screen of your device) has it's own Y axis and it points down.

Maybe you have an image in your code that is drawn on the screen but in wrong direction?


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