Decrease speed of object after touch joint is removed

Divergent_Monkey · June 1, 2017, 6:22pm

Hi,

I have two dynamic, rotating objects, A and B, that are kept together by a weld joint. The third dynamic object, C, gets connected to A with a touch joint when it comes within a certain distance. This creates the effect that A and B are magnets drawn to C when it is close enough.

When the user moves C “out of range of the magnet”, the touch joint is removed. At this point, I want A and B to stop moving. I have tried setLinearVelocity() with zero values for both x and y but A and B still move. I have also tried setting isBodyActive to false and after a few miliseconds back to true, but then they just start moving again after that.

What am I doing wrong?

Appletreeman · June 1, 2017, 6:44pm

Have you tried setting the linearDamping of the object?

Divergent_Monkey · June 1, 2017, 8:51pm

It worked like a charm, many thanks @Appletreeman!

bjsorrentino · June 1, 2017, 8:51pm

Hi @Divergent Monkey,

Can I see your basic code for this? I’m almost sure I can detect the reason when I see how you’re handling things…

Thanks,

Brent

bjsorrentino · June 1, 2017, 8:52pm

lol, I posted seconds after you did… good to hear you solved it.

Divergent_Monkey · June 2, 2017, 5:06pm

@Brent: Thanks anyway!

Divergent_Monkey · June 3, 2017, 7:45pm

@Brent: just out of curiosity, what did you suspect it was? Here is my code:

Creation of the magnet objects (A and B in my original post):

 &nbsp;-- Create visible magnet &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; local magnet = display.newImageRect("images/magnet.png", 60, 60) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.x = 100 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.y = 100 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.objectId = properties.objectId.magnet &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; physics.addBody(magnet, "dynamic", { friction = 0.0, bounce = 0.0, isSensor = true, radius = (magnet.width \* 0.5) }) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.gravityScale = 0.0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.collision = onMagnetCollision &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet:addEventListener("collision", magnet) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sceneGroup:insert(magnet) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -- Create an area in which the magnetic pull is active &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; local magnetArea = display.newCircle(levelDetails.magnets[i].x, levelDetails.magnets[i].y, 120) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.isVisible = false &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.isHitTestable = true &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.objectId = properties.objectId.magnetArea &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.stickyObject = magnet &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.stickyObject = magnetArea &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; physics.addBody(magnetArea, "dynamic", { friction = 0.0, bounce = 0.0, isSensor = true, radius = (magnetArea.width \* 0.5) }) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.gravityScale = 0.0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sceneGroup:insert(magnetArea) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -- Create a weld joint between the magnet and the magnet area so that they move together &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; local weldJoint = physics.newJoint("weld", magnet, magnetArea, 0, 0)

In the “began” phase of the collision detection of the other object (C in my original post):

if ((otherObject.isInMagnet == nil) or (otherObject.isInMagnet == false)) then timer.performWithDelay(10, function() otherObject.stickyObject.isInMagnet = true otherObject.stickyObject.touchJointMagnet = physics.newJoint("touch", otherObject.stickyObject, otherObject.x, otherObject.y) otherObject.stickyObject.touchJointMagnet.frequency = 0.30 otherObject.stickyObject.touchJointMagnet.dampingRatio = 1 otherObject.stickyObject.touchJointMagnet:setTarget(spaceship.x, spaceship.y) end) end

In the “ended” phase of the collision detection of the other object (C in my original post):

timer.performWithDelay(10, function() if (otherObject.stickyObject.isInMagnet) then otherObject.stickyObject.isInMagnet = false; otherObject.stickyObject.touchJointMagnet:removeSelf(); otherObject.stickyObject.touchJointMagnet = nil end end, 1)

The “stickyObject”-thing is just to be able to reference A from B and vice versa.

The above code gives the result that A and B still continue to move after the touch joint is removed.

bjsorrentino · June 6, 2017, 2:17am

Yeah, your code looks quite good… it’s just, as you already solved, that momentum gained from the touch joint will persist even after the joint is destroyed.

Brent

Divergent_Monkey · June 6, 2017, 6:41pm

Ok, thanks!

Appletreeman · June 1, 2017, 6:44pm

Have you tried setting the linearDamping of the object?

Divergent_Monkey · June 1, 2017, 8:51pm

It worked like a charm, many thanks @Appletreeman!

bjsorrentino · June 1, 2017, 8:51pm

Hi @Divergent Monkey,

Can I see your basic code for this? I’m almost sure I can detect the reason when I see how you’re handling things…

Thanks,

Brent

bjsorrentino · June 1, 2017, 8:52pm

lol, I posted seconds after you did… good to hear you solved it.

Divergent_Monkey · June 2, 2017, 5:06pm

@Brent: Thanks anyway!

Divergent_Monkey · June 3, 2017, 7:45pm

@Brent: just out of curiosity, what did you suspect it was? Here is my code:

Creation of the magnet objects (A and B in my original post):

 &nbsp;-- Create visible magnet &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; local magnet = display.newImageRect("images/magnet.png", 60, 60) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.x = 100 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.y = 100 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.objectId = properties.objectId.magnet &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; physics.addBody(magnet, "dynamic", { friction = 0.0, bounce = 0.0, isSensor = true, radius = (magnet.width \* 0.5) }) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.gravityScale = 0.0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.collision = onMagnetCollision &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet:addEventListener("collision", magnet) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sceneGroup:insert(magnet) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -- Create an area in which the magnetic pull is active &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; local magnetArea = display.newCircle(levelDetails.magnets[i].x, levelDetails.magnets[i].y, 120) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.isVisible = false &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.isHitTestable = true &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.objectId = properties.objectId.magnetArea &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.stickyObject = magnet &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnet.stickyObject = magnetArea &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; physics.addBody(magnetArea, "dynamic", { friction = 0.0, bounce = 0.0, isSensor = true, radius = (magnetArea.width \* 0.5) }) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; magnetArea.gravityScale = 0.0 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sceneGroup:insert(magnetArea) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; -- Create a weld joint between the magnet and the magnet area so that they move together &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; local weldJoint = physics.newJoint("weld", magnet, magnetArea, 0, 0)

In the “began” phase of the collision detection of the other object (C in my original post):

if ((otherObject.isInMagnet == nil) or (otherObject.isInMagnet == false)) then timer.performWithDelay(10, function() otherObject.stickyObject.isInMagnet = true otherObject.stickyObject.touchJointMagnet = physics.newJoint("touch", otherObject.stickyObject, otherObject.x, otherObject.y) otherObject.stickyObject.touchJointMagnet.frequency = 0.30 otherObject.stickyObject.touchJointMagnet.dampingRatio = 1 otherObject.stickyObject.touchJointMagnet:setTarget(spaceship.x, spaceship.y) end) end

In the “ended” phase of the collision detection of the other object (C in my original post):

timer.performWithDelay(10, function() if (otherObject.stickyObject.isInMagnet) then otherObject.stickyObject.isInMagnet = false; otherObject.stickyObject.touchJointMagnet:removeSelf(); otherObject.stickyObject.touchJointMagnet = nil end end, 1)

The “stickyObject”-thing is just to be able to reference A from B and vice versa.

The above code gives the result that A and B still continue to move after the touch joint is removed.

bjsorrentino · June 6, 2017, 2:17am

Yeah, your code looks quite good… it’s just, as you already solved, that momentum gained from the touch joint will persist even after the joint is destroyed.

Brent

Divergent_Monkey · June 6, 2017, 6:41pm

Ok, thanks!