Rotate A Physical Object Of 90 Degrees Sharp

[Jerome_Z]

Dear All,

 

I was wondering if someone has a trick to turn a physical object (it as to be dynamic), for instance a rectangle, to 90 degrees sharp.

 

• as the documentation mentioned you cannot used myrect.rotation=90 with dynamic body, as unpredictable results can occur, which is true

 

• I tried to apply torque or angular impulse and monitoring the angle of my object on enterFrame listener (with a fps sets at 60), but, and it is logical, you cannot reach a precise angle.

 

Any help would be appreciated.

 

Best,

Jérôme.

[bjsorrentino]

Hi Jérôme,

Can you point me to the documentation that says you shouldn’t use “object.rotation” on physical bodies? This is actually acceptable and I use it frequently. If certain documentation says otherwise, I need to correct it.

 

Thanks,

Brent

[Jerome_Z]

Hi Brent,

 

I found it here : http://docs.coronalabs.com/api/type/DisplayObject/rotation.html (in the Gotchas section)

 

and i am experiencing these famous unpredictable results.

 

Thanks,

Jérôme.

 

P.S. : my current Version is 2013.1056

[bjsorrentino]

Hi Jérôme,

Are you rotating the rectangle around an exterior reference point (top-left, etc.) instead of its center? I just tried the following code and it works as expected:

 

[lua]

local physics = require(“physics”) ; physics.start() ; physics.setGravity( 0,2 ) ; physics.setDrawMode( “hybrid” )

–make box

local box = display.newRect( 0,0,400,160 )

box.x, box.y = display.contentWidth/2, display.contentHeight/2

physics.addBody ( box, “static”, { friction=1.0 } )

–make ball

local ball = display.newCircle( 0,0,20,20 )

ball.x, ball.y = display.contentWidth/2+40, display.contentHeight/2-200

physics.addBody ( ball, “dynamic”, { radius=20, bounce=0.6, friction=0.3 } )

–rotate box after 4 seconds

local function boxRotate()

box.rotation = 45

end

timer.performWithDelay(4000,boxRotate,1)

[/lua]

 

Try this and see if you get the expected results…

Brent

[Jerome_Z]

Thanks Brent,

 

in fact, what I am trying to do is to rotate a group as :

local physics = require("physics") ; physics.start() ; physics.setGravity( 0,0 ) ; physics.setDrawMode( "hybrid" ) --make box local grpBox = display.newGroup() local box1 = display.newRect( 0,0,40,40 ) box1.x, box1.y = display.contentWidth/2, display.contentHeight/2 local box2 = display.newRect( 0,0,40,40 ) box2.x, box2.y = box1.x+40, box1.y local box3 = display.newRect( 0,0,40,40 ) box3.x, box3.y = box2.x+40, box1.y grpBox:insert(box1) grpBox:insert(box2) grpBox:insert(box3) grpBox:setReferencePoint(display.CenterReferencePoint) physics.addBody ( box1, "dynamic", { friction=1.0 } ) physics.addBody ( box2, "dynamic", { friction=1.0 } ) physics.addBody ( box3, "dynamic", { friction=1.0 } ) --rotate box after 4 seconds local function boxRotate() grpBox.rotation = grpBox.rotation + 45 end timer.performWithDelay(400,boxRotate,0)

 

 

 

so you can see that the physics not follow, that why I was thinking to use physic to handle my rotation.

 

Txs,

Jérôme.

[bjsorrentino]

Hi Jérôme,

OK, this is expected behavior then. You can’t rotate or shift display groups of physics items around independently of each other, or the collision system will become inaccurate, as you’re seeing. I recently suggested a method to another user which basically “pre-calculates” the location of where physics objects would be when rotated around a non-center reference point (or in this case, rotated inside a group). Then it moves and rotates the objects to that position but keeps the group in the same coordinate space so collisions maintain their integrity.

 

http://forums.coronalabs.com/topic/32895-using-eg-topleftalign-on-a-physics-body-only-applies-to-its-appearance-not-its-body-help/

 

I don’t know if this will work for your scenario, but you could try it…

 

Brent

[Jerome_Z]

Hi Brent,

 

It works like a charm. 

 

Many thanks for the trick,

Best,

Jérôme.

[bjsorrentino]

Hi Jérôme,

Can you point me to the documentation that says you shouldn’t use “object.rotation” on physical bodies? This is actually acceptable and I use it frequently. If certain documentation says otherwise, I need to correct it.

 

Thanks,

Brent

[Jerome_Z]

Hi Brent,

 

I found it here : http://docs.coronalabs.com/api/type/DisplayObject/rotation.html (in the Gotchas section)

 

and i am experiencing these famous unpredictable results.

 

Thanks,

Jérôme.

 

P.S. : my current Version is 2013.1056

[bjsorrentino]

Hi Jérôme,

Are you rotating the rectangle around an exterior reference point (top-left, etc.) instead of its center? I just tried the following code and it works as expected:

 

[lua]

local physics = require(“physics”) ; physics.start() ; physics.setGravity( 0,2 ) ; physics.setDrawMode( “hybrid” )

–make box

local box = display.newRect( 0,0,400,160 )

box.x, box.y = display.contentWidth/2, display.contentHeight/2

physics.addBody ( box, “static”, { friction=1.0 } )

–make ball

local ball = display.newCircle( 0,0,20,20 )

ball.x, ball.y = display.contentWidth/2+40, display.contentHeight/2-200

physics.addBody ( ball, “dynamic”, { radius=20, bounce=0.6, friction=0.3 } )

–rotate box after 4 seconds

local function boxRotate()

box.rotation = 45

end

timer.performWithDelay(4000,boxRotate,1)

[/lua]

 

Try this and see if you get the expected results…

Brent

[Jerome_Z]

Thanks Brent,

 

in fact, what I am trying to do is to rotate a group as :

local physics = require("physics") ; physics.start() ; physics.setGravity( 0,0 ) ; physics.setDrawMode( "hybrid" ) --make box local grpBox = display.newGroup() local box1 = display.newRect( 0,0,40,40 ) box1.x, box1.y = display.contentWidth/2, display.contentHeight/2 local box2 = display.newRect( 0,0,40,40 ) box2.x, box2.y = box1.x+40, box1.y local box3 = display.newRect( 0,0,40,40 ) box3.x, box3.y = box2.x+40, box1.y grpBox:insert(box1) grpBox:insert(box2) grpBox:insert(box3) grpBox:setReferencePoint(display.CenterReferencePoint) physics.addBody ( box1, "dynamic", { friction=1.0 } ) physics.addBody ( box2, "dynamic", { friction=1.0 } ) physics.addBody ( box3, "dynamic", { friction=1.0 } ) --rotate box after 4 seconds local function boxRotate() grpBox.rotation = grpBox.rotation + 45 end timer.performWithDelay(400,boxRotate,0)

 

 

 

so you can see that the physics not follow, that why I was thinking to use physic to handle my rotation.

 

Txs,

Jérôme.

[bjsorrentino]

Hi Jérôme,

OK, this is expected behavior then. You can’t rotate or shift display groups of physics items around independently of each other, or the collision system will become inaccurate, as you’re seeing. I recently suggested a method to another user which basically “pre-calculates” the location of where physics objects would be when rotated around a non-center reference point (or in this case, rotated inside a group). Then it moves and rotates the objects to that position but keeps the group in the same coordinate space so collisions maintain their integrity.

 

http://forums.coronalabs.com/topic/32895-using-eg-topleftalign-on-a-physics-body-only-applies-to-its-appearance-not-its-body-help/

 

I don’t know if this will work for your scenario, but you could try it…

 

Brent

[Jerome_Z]

Hi Brent,

 

It works like a charm. 

 

Many thanks for the trick,

Best,

Jérôme.