GameObject euler.z problem

Questions
#1

Hello! I made a gameobject and set its rotation manually to 0,0,105. But when I’m trying to get euler.z in my script using go.get(".", “euler.z”) it gives me 75. Why?

#2

I’m just trying to make a rotating object which I can start and stop. To make it I use example from here https://www.defold.com/examples/animation/spinner/.

#3

I am not sure what’s the current situation with the euler property, but it wasn’t working properly. You can use quaternions that are inside the rotation property. To set a rotation on the Z axis you would do

go.set_rotation(vmath.quat_rotation_z(math.pi))
#4

Ok. I need to rotate object constantly with same speed. Rotation should start from current rotation value. How can I achieve these result? Example in the docs works only when initial z angle of object is 0.

May be I should get angle from quaternion somehow if

go.get(".", "euler.z")

is buggy?
Something like:

    local rot = go.get_rotation()

    -- this is the main line
    local original_angle = vmath.get_angle_from_quaternion_somehow(rot)

    self.t = self.t + dt 
    local step = math.floor(self.t * self.speed) 
    local angle = math.pi / 6 * step + original_angle
    local rot = vmath.quat_rotation_z(-angle) 
    go.set_rotation(rot)
#5

I think this post (and links in this post) can help you Alternative to quaternions (SOLVED)

#6

So, ok! Huh! I solved it. Works with go.set_rotation(). If you want to make a constantly rotating object you should add its initial rotation to angle calculated for next frame. And finally that’s what I’ve got:

function init(self)
    self.original_rot = go.get_rotation()
    self.rotate = false
    self.t = 0
end

function rotate(self, dt)
    self.t = self.t + dt
    local step = math.floor(self.t * self.speed)
    local angle = math.pi / 360 * step
    local rot = vmath.quat_rotation_z(-angle)

    -- this line is key to dzen
    go.set_rotation(rot * self.original_rot)
end

function update(self, dt)
    if self.rotate then
        rotate(self, dt)
    end
end


function stop_rotation(self)
    self.rotate = false
end


function start_rotation(self)
    self.rotate = true
    self.original_rot = go.get_rotation()
end
#7

You can do it a bit simpler.

function update(self, dt)
    if self.rotate then
        go.set_rotation(go.get_rotation() * vmath.quat_rotation_z(self.step_angle))
    end
end

Define self.step_angle as a rotation increment in radians.

1 Like
#8

So, what is your version defining self.stap_angle? :wink:

#9

Whatever value suits you, like maybe 0.001

#10

And perhaps also apply dt to the step_angle before use.

2 Likes