Box2d DstanceJoint

gaboritaly

Hi ,
I little modified the Arturs code http://appcodingeasy.com/Gideros-Mobile/Dragging-Box2d-object-in-Gideros-Mobile
Added the distancejoint, but not work well how I waited, isn't fluid and isn't maintain the distance (it's similar to rope joint, what I would like in the future ).
I want to doing the examples what I found here, if you click on the photo will ope the live Flash examples.
http://blog.allanbishop.com/box2d-2-1a-tutorial-part-2-joints/
I would learn ad doing that effect in Gideros.
My questions are:
How can I set the distance between 2 object?
How can I fix the the distance between 2 objects without enlarge ?
When I click on the circle why has a strange animation with choppy ?
In the reference manual I found 2 groups in manual :
1)
Distance Joint

Distance joint definition. This requires defining an anchor point on both bodies and the non-zero length of the distance joint. The definition uses local anchor points so that the initial configuration can violate the constraint slightly. This helps when saving and loading a game.

type: (number) b2.DISTANCE_JOINT
bodyA: (b2.Body) The first attached body.
bodyB: (b2.Body) The second attached body.
collideConnected: (boolean) Set this flag to true if the attached bodies should collide.
localAnchorA: (table) The local anchor point relative to bodyA’s origin.
localAnchorB: (table) The local anchor point relative to bodyB’s origin.
length: (number) The natural length between the anchor points. Do not use a zero or short length.
frequencyHz: (number) The mass-spring-damper frequency in Hertz.
dampingRatio: (number) The damping ratio. 0 = no damping, 1 = critical damping.
2)
b2.createDistanceJointDef(bodyA, bodyB, anchorAx, anchorAy, anchorBx, anchorBy)

What is the difference 2 chapter, and how can I use well them ?

Sorry for a lot of questions, but for me is it really hard to learn without code examples in the documentations.
And thank you in advance to be patience and help.

this my code

require "box2d"   local physicsScale = 30 b2.setScale(physicsScale)   local world = b2.World.new(0, 10, true)   -- for creating objects using shape -- as example - bounding walls function wall(x, y, width, height, name) local wall = Shape.new() --define wall shape wall:beginPath() --we make use (0;0) as center of shape, --thus we have half of width and half of height in each direction wall:moveTo(-width/2,-height/2) wall:lineTo(width/2, -height/2) wall:lineTo(width/2, height/2) wall:lineTo(-width/2, height/2) wall:closePath() wall:endPath() wall:setPosition(x,y)   --create box2d physical object local body = world:createBody{type = b2.STATIC_BODY} body:setPosition(wall:getX(), wall:getY()) body.name= name --body:setAngle(wall:getRotation() * math.pi/180) local poly = b2.PolygonShape.new() poly:setAsBox(wall:getWidth()/2, wall:getHeight()/2) local fixture = body:createFixture{shape = poly, density = 1.0, friction = 0.1, restitution = 0.8} wall.body = body wall.body.type = "wall"   --add to scene stage:addChild(wall)   --return created object return wall end   local screenH = application:getContentHeight() local screenW= application:getContentWidth()   --create bounding walls outside the scene wall(-dx,screenH/2,10,screenH) --left wall(screenW/2,-dy,screenW+2*dx,10) --top wall(screenW+dx,screenH/2,10,screenH)--right wall(screenW/2,screenH,screenW+2*dx,10) --bottom   --create empty box2d body for joint --since mouse cursor is not a body --we need dummy body to create joint local ground = world:createBody({})   --joint with dummy body local mouseJoint = nil local distanceJoint = nil -- create a mouse joint on mouse down function onMouseDown(event) if ball:hitTestPoint(event.x, event.y) then --ball.body:setPosition(event.x, event.y) local jointDef = b2.createMouseJointDef(ground, ball.body, event.x, event.y, 100000) mouseJoint = world:createJoint(jointDef) end end   -- update the target of mouse joint on mouse move function onMouseMove(event) if mouseJoint ~= nil then mouseJoint:setTarget(event.x, event.y) end end   -- destroy the mouse joint on mouse up function onMouseUp(event) if mouseJoint ~= nil then world:destroyJoint(mouseJoint) mouseJoint = nil end end -- for creating objects using image -- as example - ball function createBall(x, y) --create ball bitmap object from ball graphic local ball = Bitmap.new(Texture.new("ball.png")) --reference center of the ball for positioning ball:setAnchorPoint(0.5,0.5)   ball:setPosition(x,y)   --get radius local radius = ball:getWidth()/2   --create box2d physical object local body = world:createBody{type = b2.DYNAMIC_BODY} body.name ='ball' print(ball:getX()..' '.. ball:getY()) body:setPosition(ball:getX(), ball:getY()) body:setAngle(ball:getRotation() * math.pi/180) local circle = b2.CircleShape.new(0, 0, radius) local fixture = body:createFixture{shape = circle, density = 1.0, friction = 0.1, restitution = 0.8} ball.body = body ball.body.type = "ball"   --add to scene stage:addChild(ball)   --return created object return ball end   ball =createBall(application:getContentWidth()/2, 100) ball1 =createBall(200, 200)   local dj = b2.createDistanceJointDef(ball.body, ball1.body, 0, 0, 0, 0, 100) distanceJoint = world:createJoint(dj) --distanceJoint.setDampingRatio(0) not work     function onEnterFrame() -- edit the step values if required. These are good defaults! world:step(1/60, 8, 3) --iterate through all child sprites for i = 1, stage:getNumChildren() do --get specific sprite local sprite = stage:getChildAt(i) -- check if sprite HAS a body (ie, physical object reference we added) if sprite.body then --update position to match box2d world object's position --get physical body reference local body = sprite.body --get body coordinates local bodyX, bodyY = body:getPosition() --apply coordinates to sprite sprite:setPosition(bodyX, bodyY) --apply rotation to sprite sprite:setRotation(body:getAngle() * 180 / math.pi) end end end   local debugDraw = b2.DebugDraw.new() world:setDebugDraw(debugDraw) stage:addChild(debugDraw)     stage:addEventListener(Event.ENTER_FRAME, onEnterFrame) -- register for mouse events stage:addEventListener(Event.MOUSE_DOWN, onMouseDown) stage:addEventListener(Event.MOUSE_MOVE, onMouseMove) stage:addEventListener(Event.MOUSE_UP, onMouseUp)

ar2rsawseen

Hello,
this line:

local dj = b2.createDistanceJointDef(ball.body, ball1.body, 0, 0, 0, 0, 100)

should be:

local dj = b2.createDistanceJointDef(ball.body, ball1.body, application:getContentWidth()/2, 100, 200, 200)

taken from:

ball =createBall(application:getContentWidth()/2, 100) ball1 =createBall(200, 200)

As stated in b2.createDistanceJointDef definition docs

anchorAx: (number) the x coordinate of the world anchor point of bodyA
anchorAy: (number) the y coordinate of the world anchor point of bodyA
anchorBx: (number) the x coordinate of the world anchor point of bodyB
anchorBy: (number) the y coordinate of the world anchor point of bodyB

All of them are the coordinates of the world

Other definition is a definition of DISTANCE_JOINT object which is returned by

distanceJoint = world:createJoint(dj)

these are probably it's properties and somewhere in docs there are also methods defined.

You provided a really interesting link, I'll create similar examples with Gideros when I'll have time

Edited:
Ok, other definition if you do not want to create joint definition using b2.createDistanceJointDef but create table with described properties and pass it to world:createJoint your self. Don't know, never tried and used it. I always prefer to use proper createSomeJoint method

gaboritaly

You are BIG >- >- >- >- >- >- >- >-
Thank you @ar2rsawseen, Im thinking work similar to setAnchorpoint ..
Well now learning box2d, and probe doing that examples.
If you want, I can post here ,and you can control it.
I'm really sure, I'll need some times your knowledge )

ar2rsawseen

Sure post what you have here, and if any obstacles, we'll try to figure out together

ar2rsawseen

Here's the post with Gideros joint examples:
http://appcodingeasy.com/Gideros-Mobile/Using-box2d-joints-in-Gideros