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Inverted gravity problem

Posted: Wed Apr 12, 2017 3:36 am
by jdleung
I'm using jbox2d 2.2.1.1 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?

Thanks.

Re: Inverted gravity problem

Posted: Sun Apr 23, 2017 7:57 am
by JeneaV
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?

Image