Rotation Joints dont allign together when spinning

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THE_NOTORIOUS_PIGGY

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Posted: 31st May 2018 18:35

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I have a problem in my current game. I have a rotational joint between the ball and and the base, and I want the stick sprite to rotate around the same position as my rotational joint. Let me explain.
It's meant to look like this, which works well most of the time:

however, depending on device, especially on middle-lower end devices, it looks like this:

Here is a debug screenshot so you can see exactly whats up

this is the code for the stick object

+ Code Snippet

//spin joint
jointspin = jointspin - value
SetSpriteAngle(jointbase1,jointspin)

this is the code for the joint

global rotatespeed as integer = 1000000
rotatedirection = 20

+ Code Snippet

//create joint
	if GetJointExists(1) = 0
		CreateRevoluteJoint( 1, ball, jointlink, 210, 210, 1 )
	endif
	//set rotation
	SetJointMotorOn( 1, rotatedirection, rotatespeed )

I've had this problem for months and I am just steps away from releasing this game (my biggest project) onto the iOS App store and I want to have this game perfect. Any help on fixing this is appreciated.

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CJB

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Posted: 31st May 2018 19:29

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I can't see your images

Aaargh! Ducks!
Phone Tap!
Uzmadesign

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Bengismo

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Posted: 31st May 2018 19:37 Edited at: 31st May 2018 19:39

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Link 1

Link 2

Link 3

Fixed those links for you.....

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Bengismo

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Posted: 31st May 2018 19:47 Edited at: 31st May 2018 19:50

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And your setting a constant rate of movement for the link rotation and assuming that that will tie up with the physics simulation of the ball.... by the looks of it. Unfortunately that wont be the case unless your framerate is perfectly constant.

Best thing to do would be to work out the angle of the ball from the stick and set the angle of the link to be equal to that.

Technically speaking the revolute joint should be between the vertical stick and the rotating link arm and the ball should have a weld joint to the link arm. Thats the way id of tried it unless there is a reason not to.

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THE_NOTORIOUS_PIGGY

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Posted: 31st May 2018 21:29

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@Bengismo thank you very much for the photos, I dont know how i messed that up. but that is an interesting point. What if I get the x & y's of both the ball and the static part of the rotator, then is there a formula that I can use to find the angle between them? and then simply set the angle of my sprite object as that value? Is there a formula like that?

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Bengismo

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Posted: 1st Jun 2018 13:43 Edited at: 1st Jun 2018 13:45

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To find an angle from an x and y offset you use ATanFull()

Or just use this code below to point the link arm at the ball (AngleOffset is 0 unless your link arm sprite was loaded sideways or upside down then its 90 or 180 etc..)

+ Code Snippet


RotateSpriteToPointAt(LinkArm,Ball,0)

function RotateSpriteToPointAt(Spr, Target, AngleOffset)
	
	// Calculate the angle to the target object
	Angle# = ATanFull(GetSpriteXByOffset(Target) - GetSpriteXByOffset(Spr),GetSpriteYByOffset(Target)- GetSpriteYByOffset(Spr)) + AngleOffset
	SetSpriteAngle(Spr,Angle#)
	
endfunction

That will work.

As I said above...personally id create 2 joints ....the revolute joint between the post and the link arm then a weld joint for the ball to the link arm to do it properly

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smallg

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Posted: 1st Jun 2018 19:29

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i believe you're trying to do this?

SetVirtualResolution(1024,768)
SetSyncRate(60,1)

//create the bar to hold the ball and chain
bar1 = CreateSprite(0)
SetSpriteSize(bar1,10,260)
SetSpritePositionByOffset(bar1,512,500)
SetSpritePhysicsOn(bar1,1)

//create the chain
chain = CreateSprite(0)
SetSpriteSize(chain,10,80)
SetSpritePositionByOffset(chain,512,GetSpriteY(bar1)-(GetSpriteHeight(chain)*0.5))
SetSpriteColor(chain,255,0,0,255)
SetSpriteCollideBit(chain,2,0)
SetSpritePhysicsOn(chain,2)
//join the bar and chain
joint1 = CreateRevoluteJoint( bar1, chain, 512, GetSpriteY(bar1), 0 ) 
//create the ball on the end of the chain
ball = CreateSprite(0)
SetSpriteSize(ball,30,30)
SetSpritePositionByOffset(ball,512,GetSpriteY(chain)-(GetSpriteHeight(ball)*0.5))
SetSpritePhysicsOn(ball,2)
//join the ball and the chain
CreateRevoluteJoint( ball, chain, 512, GetSpriteY(chain), 0 ) 
//create the floor
ground = CreateSprite(0)
SetSpriteSize(ground,1024,268)
SetSpritePosition(ground,0,500)
SetSpritePhysicsOn(ground,1)
SetSpriteCollideBit(ball,2,1)
SetSpriteCollideBit(ball,1,0)
SetJointMotorOn( joint1, 1000, 10000)
//create a falling box for the ball to hit while swinging
box = CreateSprite(0)
SetSpriteCategoryBit(box,2,1)
SetSpriteCategoryBit(box,1,0)
SetSpriteSize(box,20,20)
repeat 
	temp = random2(412,612)
until temp <> 512
SetSpritePositionByOffset(box,temp,200)
SetSpritePhysicsOn(box,2)

do 
	if GetRawKeyPressed(27) then end 
	
	if GetSpriteCollision(ground,box)
		repeat 
			temp = random2(412,612)
		until temp <> 512
		SetSpritePositionByOffset(box,temp,200)
	endif

sync()
loop

+ Code Snippet

SetVirtualResolution(1024,768)
SetSyncRate(60,1)

//create the bar to hold the ball and chain
bar1 = CreateSprite(0)
SetSpriteSize(bar1,10,260)
SetSpritePositionByOffset(bar1,512,500)
SetSpritePhysicsOn(bar1,1)

//create the chain
chain = CreateSprite(0)
SetSpriteSize(chain,10,80)
SetSpritePositionByOffset(chain,512,GetSpriteY(bar1)-(GetSpriteHeight(chain)*0.5))
SetSpriteColor(chain,255,0,0,255)
SetSpriteCollideBit(chain,2,0)
SetSpritePhysicsOn(chain,2)
//join the bar and chain
joint1 = CreateRevoluteJoint( bar1, chain, 512, GetSpriteY(bar1), 0 ) 
//create the ball on the end of the chain
ball = CreateSprite(0)
SetSpriteSize(ball,30,30)
SetSpritePositionByOffset(ball,512,GetSpriteY(chain)-(GetSpriteHeight(ball)*0.5))
SetSpritePhysicsOn(ball,2)
//join the ball and the chain
CreateRevoluteJoint( ball, chain, 512, GetSpriteY(chain), 0 ) 
//create the floor
ground = CreateSprite(0)
SetSpriteSize(ground,1024,268)
SetSpritePosition(ground,0,500)
SetSpritePhysicsOn(ground,1)
SetSpriteCollideBit(ball,2,1)
SetSpriteCollideBit(ball,1,0)
SetJointMotorOn( joint1, 1000, 10000)
//create a falling box for the ball to hit while swinging
box = CreateSprite(0)
SetSpriteCategoryBit(box,2,1)
SetSpriteCategoryBit(box,1,0)
SetSpriteSize(box,20,20)
repeat 
	temp = random2(412,612)
until temp <> 512
SetSpritePositionByOffset(box,temp,200)
SetSpritePhysicsOn(box,2)

do 
	if GetRawKeyPressed(27) then end 
	
	if GetSpriteCollision(ground,box)
		repeat 
			temp = random2(412,612)
		until temp <> 512
		SetSpritePositionByOffset(box,temp,200)
	endif

	
	sync()
loop

i'm not an expert by any means but it looks good to me.

if you don't want the ball to rotate around on it's own axis then use a different type of joint as bengismo says

life's one big game
spec= 4ghz, 16gb ram, AMD R9 2700 gpu

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THE_NOTORIOUS_PIGGY

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Posted: 1st Jun 2018 20:44

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Hello guys. Thank you so much for your help. For the first time ever I used ATanFull(), and this has worked exactly how I wanted it to. I did this:

+ Code Snippet

s_angle# = ATanFull(210 - GetSpriteXByOffset(ball), 210 - GetSpriteYByOffset(ball))
print("s_angle = " + str(s_angle#))

//spin joint
SetSpriteAngle(jointbase1,s_angle#)

This simple 2 line solutions has costed me months of stress because I couldn't figure out how to deal with this issue properly. Thank you @Bengismo.

As for @smallg, that is done in a different way from what my game is already built up upon, but seeing that great video you made, I have gotten a lot of ideas to use that in a separate game. May I have your permission to possibly use that code segment in another game? Thank you.

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smallg

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Posted: 2nd Jun 2018 08:53

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Of course

life's one big game
spec= 4ghz, 16gb ram, AMD R9 2700 gpu

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