[RESOLVED] Question - Rotate object through touch

Solar2D General Questions/Discussion
#21

I’ve come across another challenge with this spinning code. I’m now using it to spin a steering wheel, then have the car react as a result.

I don’t understand why the “rotation” value of my item starts at 0, and sometimes:

  1. goes up to 180 as I turn it to the right, and flicks to a negative value (say -179) when I get completely upside down, using negative values increasing to 0 as I continue to turn the item to the right and back to vertical (0).

  2. goes up to some other value (say 43) as I turn to the right, then flicks to a large negative (-317), increasing to zero as I continue to turn to the right.

  3. goes all the way to 360 as I turn to the right, and back to 0 when I return to the top.

It seems to change based on where on the wheel I grab to start turning. Bizarrely the car seems to take on the same rotation numbers at the same time (i.e. -55 on the wheel = -55 for the car, even though -55 may be a completely different on-screen angle in example 1 vs example 2).

Is there a way to make this consistent so that I can use the difference between the wheel rotation and the car rotation to define the torque that I want to apply to the car?

Thanks,

Nathan.

#22

Hi Nathan,

You may want to try this code, which should control the “flick to opposite” behavior that you’re describing. This code calculates the angle between your object (at “srcX”/“srcY”) and a touch (at “dstX”/“dstY”), which may not be how your control actually works, but parts of the code can be parsed out and implemented as you see fit.

[lua]

local function angleBetween( srcX, srcY, dstX, dstY )

        local angle = ( math.deg( math.atan2( dstY-srcY, dstX-srcX ) )+90 )

        if ( angle < 0 ) then angle = angle + 360 end ; return angle % 360

end

[/lua]

Hope this helps,

Brent

#23

Brent,

Woohoo - looks like the problem is fixed. I used your line “if ( angle < 0 ) then angle = angle + 360 end ; return angle % 360” to “fix” the angles being returned by rotation, so they reliably went from 0-360.

Thanks,

Nathan.