How to use Accelerometer with a Box2d Body?

Mells

Hi all,

the other day I was trying to control a Box2d Body with the accelerometer.
The example I have found in the documentation uses setPosition() to move a Sprite, but as stated in this thread :
What is the right way to move a body?
setPosition() should be avoided for Bodies.

Although I have found this article by @ar2rsawseen :
Using Accelerometer with Box2d in Gideros
the method described in the article modifies the whole world's gravity

self.world:setGravity(self.fx*self.gravityScale, -self.fy*self.gravityScale)

I would like the accelerometer to control only one Box2d body.

How would you solve it?

Thank you

hgvyas123

in the case there are more than one dynamic body then obviously you can't use setgravity to control only one dynamic body

so you can use setlinearvelocity and applyforce [actually gravity is also one kind of force multiplied with the mass of body and applied each time] for them

also as you said setPosition() "SHOULD" be avoided for Bodies.

Mells

@hgvyas
thank you.
Well you know I already came to the same conclusions by reading the articles

The thing is : how does the formula apply with accelerometer?

If anybody's done that before that would help (if I could avoid reinvent the wheel).
If not I will try again when I have more time but I believe it involves maths which is not my forte.

hgvyas123

i think putting this lines in enterframe will do the work

local x, y, z = accelerometer:getAcceleration()   local tempX,tempY = body:getLinearVelocity() -- to store the current y speed body:setLinearVelocity(x*10,tempY) -- change number 10 as per your need

hgvyas123

ofcourse after starting the accelerometer with below code

local accelerometer = Accelerometer.new() accelerometer:start()

Mells

@hgvyas123 thank you for trying many times

Actually the effect is a bit different : to keep the body stationary, on your solution the player needs to keep the device flat, while with the other solution if the player keeps the device at an angle and doesn't move, the body doesn't move too.

I believe the solution involves calculating velocity by checking the distance between x/y Acceleration at the previous frame, and the current frame, and do something with it...
I am not sure I'm on the right track.
@ar2rsawseen do you have an article about that on your site? i think I have searched the archives and didn't find.
I will search on the forums more..

Mells

For now this is the closest that I could get but I am not sure it's the best way to do it :

local prevX, prevY, prevZ, sensitivity   sensitivity = 3000   -- Get accelerometer values on first frame if (prevX == nil) and (prevY == nil) and (prevZ == nil) then prevX, prevY, prevZ = accelerometer:getAcceleration() end   -- get accelerometer values x, y, z = accelerometer:getAcceleration()   -- do the low-pass filtering fx = x * filter + fx * (1 - filter) fy = y * filter + fy * (1 - filter) fz = z * filter + fz * (1 - filter)   prevFx = prevX * filter + fx * (1 - filter) prevFy = prevY * filter + fy * (1 - filter) prevFz = prevZ * filter + fz * (1 - filter)   -- Position self.playerRef.body:setLinearVelocity((prevFx-fx) * sensitivity, -(prevFy-fy) * sensitivity)   -- get accelerometer values prevX, prevY, prevZ = accelerometer:getAcceleration()

But anyway, if it helps someone...

zvardin

If you want the body to accelerate to its top speed you will probably want to use applyLinearImpulse, otherwise I'd stick with the setLinearVelocity like you're doing.

I found this helpful for acceleration to a max speed: http://www.iforce2d.net/b2dtut/constant-speed