Shoot projectile from a tank barrel?

Okay, here’s a fun one.
I’m making this tank game. I have a simple model. The barrel of the tank is a separate model that is childed to the tank “character,” and rotates yaw and pitch with the mouse.

On a mouse click I have it instantiate a ball and ApplyForce to shoot it across the map. I’m having trouble instantiating the ball at the end of the barrel.

Here are the relevant sections:

--makes the tank. I've taken out the wheels and other parts. Below is the hull and the turret top with the barrel
function CreateCharacter()
    characterNode = scene_:CreateChild("Player")
    characterNode.position = Vector3(0.0,0.0, 0.0)
    main= characterNode:CreateChild("Player")
    main.position = Vector3(0.0, 0.0, 0.0)
    local object = main:CreateComponent("StaticModel")
    object.model = cache:GetResource("Model", "Models/hull.mdl")

    local body = characterNode:CreateComponent("RigidBody")
    body.collisionLayer = 1
    body.mass = 100.0
    body.angularFactor = Vector3(0.0, 1.0, 0.0)
    body.collisionEventMode = COLLISION_ALWAYS
    body:SetAngularDamping(.9)
    body:SetLinearDamping(.9)
    local shape = characterNode:CreateComponent("CollisionShape")
    shape:SetBox(Vector3(3.6,1.8,7.5))

    barrel= characterNode:CreateChild("Player")
    barrel.position = Vector3(0.0, 0, 0.0)
    local barrel = tube:CreateComponent("StaticModel")
    barrel.model = cache:GetResource("Model", "Models/top.mdl")

...

end

--this just creates a bullet
function Shoot()
    local pos=characterNode:GetPosition()
    local objectNode = scene_:CreateChild("Box")
objectNode.position=Vector3(characterNode.position.x,characterNode.position.y+1.8,characterNode.position.z) + objectNode.rotation* Quaternion(character.controls.yaw, Vector3(0.0, 1.0, 0.0))* Quaternion(character.controls.pitch, Vector3(0.0, 0.0, 1.0)) * Quaternion(0,90,-character.controls.pitch)
        local yaw = Quaternion(character.controls.yaw+90, Vector3(0.0, 1.0, 0.0))
        local pitch=Quaternion(character.controls.pitch, Vector3(0.0, 0.0, 1.0))
        local dir = yaw * pitch
	    objectNode.rotation=dir
        objectNode:SetScale(Vector3(.5,.5,.5))
        local object = objectNode:CreateComponent("StaticModel")
        object.model = ball

        local body = objectNode:CreateComponent("RigidBody")
        body.mass = 2
        body.collisionEventMode = COLLISION_ALWAYS
        local shape = objectNode:CreateComponent("CollisionShape")
        shape:SetBox(Vector3(1.0, 1.0, 1.0))
        body:ApplyImpulse(objectNode.rotation*Vector3(0,0,1)*500)
end

Screenshot1366×732 242 KB

Forward direction is z for all object.
Set your object global rotation to the tank rotation before impulse. There is the same thread by GodMan a few days back.

Ok cool, so pitch and yaw are good now.
Any idea on how to get the position of the end of the rotated barrel for instantiating the bullet?

To get the barrels position assuming it model origins are 0,0,0. You could get the nodes worldPosition then offset it like this worldPosition + Vector3(0,0,2.0f); you will have to play with offset some to get it right. Then use that position to spawn you missle

I just went over your other thread. I didn’t mean to re-ask the same thing, but yours didn’t show up as a “similar thread,” while writing this one.
Anyways, that’s what I was trying, but I guess it’s because the model needs to rotate in the center, making the barrel do a wide arc. And the bullet needs to come from the barrel…
For the time being I just made a dummy uncollidable body attached to the end of the barrel and I take its position haha. It’s a little dumb but it works.

I was also going to suggest that in a 3d editor you could add a dummy or bone at the end of the barrel. Then give urho3d that bone or dummy as a node. Then get it’s position like any other node. I have done that for many things.

Seems simple enough! I should really use the editor more lol. I’ll mark that as the solution, although I did it via code.
It’s funny that I was racking my head over Quaternions when something stupidly simple works immediately.

I add mine to model in 3ds max that I know will need it. Like a character that needs to spawn something.