Any way to drag&drop static box2d objects?

rrraptor · September 2016

Hi there.
So, i need to D&D static box2d objects, but dynamic objects shoud correctly react to that. For example, if i have dragable platform (static object) at the bottom of the screen and dynamic box above it, then when i move platform from bottom to top, box shoud gain impulse and bounce from platform when i drop platform.
I was trying to use mouse joint, but it didnt work.
Any other solutions?
Simple project attached (just in case)

And another quick question. How to correctly override Sprite methods setX, setY, setPosition and e.t.c.? Right now i have something like this:

function Box:setX2(x)
	self:setX(x)
	self._body_pos[1] = x
	self.body:setPosition(x, self._body_pos[2])
end
 
function Box:setY2(y)
	self:setY(y)
	self._body_pos[2] = y
	self.body:setPosition(self._body_pos[1], y)
end
 
function Box:setPosition2(x,y)
	self:setPosition(x, y)
	self._body_pos[1] = x
	self._body_pos[2] = y
	self.body:setPosition(x, y)
end

antix · September 2016

A static body is really just that, static. I don't think you should move them. Maybe instead use a Kinematic body which behave pretty much like a static body, but can be moved.

smdulgeroglu · September 2016

You can use mouse joint just You mentioned before. But according to my experience sometimes mouse joint can be laggy however it updates its position with respect to the joint target. box2d has setTransform method which is used to set bodies' angle and position, in gideros I presume setPosition and set angle methods are used instead. I used it and have not observed weird and buggy behaviors.

In short, you can use setPosition method outside of the world:step method. This means, do not use it in box2d callbacks(PRESOLVE,POSTSOLVE,BEGIN_CONTACT etc).

smdulgeroglu · September 2016

In addition using kinematic bodies does not solve your problem. Outside agents such as force and impulses does not affect Kinematic bodies. Kinematic bodies can only moved by setting its velocity by manually. Again if you decide to use it and not use the setPosition method. You have to deal with some maths and time intervals metric and pixel conversions etc. I believe you can achive your goal by just experimenting the ideas in box2d community.

rrraptor · September 2016

You can use mouse joint just You mentioned before.

No, i cant.

In short, you can use setPosition method outside of the world:step method. This means, do not use it in box2d callbacks(PRESOLVE,POSTSOLVE,BEGIN_CONTACT etc).

Yeah, i know it, world is locked when these events dispatched.

Well, i think i can do it by using only dynamic bodies, but with 0 gravity. And for non dragable objects apply impulse/set angular velocity. Idk, need to try.

rrraptor · September 2016

use a Kinematic body

I'll try

antix · September 2016

You can set a kinematic bodies position manually and if still works as it should. Kinematic bodies do not react to forces but neither do static bodies. I don't think @rrraptor was wanting forces to affect the static bodies was he?

rrraptor · September 2016

@antix emm...it didnt work with setPosition (kinematic body). Maybe im doing something wrong..?
Anyway, i solved my problem

Here is a gif:

I'm just setting the linear velocity like:

body:setLinearVelocity(targetX - x, targetY - y)

Where x, y - body current position.
Project attached.

Howdy, Stranger!

Categories

In this Discussion

Top Posters

Any way to drag&drop static box2d objects?

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

Any way to drag&drop static box2d objects?

Comments