Generally what I'm trying to achieve: we have map data that historically was all 2D, and the coordinate system we use is the origin point (0,0) at the top left, positive x goes right, positive y goes down. We have now added 3D data by adding a z axis, positive z coming out of the screen towards you (think top-down map view). This is a left handed coordinate system, but SceneKit is a right handed coordinate system. I would like to apply some transform at the top level of my SceneKit Scene that will convert the Scene into a left handed coordinate system such that I can modify/position/add nodes to the scene in terms of our custom mapping coordinate system and things will just work.
So far I have this:
let scene = SCNScene()
let cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
cameraNode.scale = SCNVector3(1,-1,1)
scene.rootNode.addChildNode(cameraNode)
This achieves exactly what I want, but has one big problem. It inverts all of the geometry faces, so my geometry's disappear unless I change their material's cullMode:
let mapLength = 1000 //max X axis
let mapWidth = 800 //max Y axis
let mapHeight = 100 //max Z axis
cameraNode.position = SCNVector3(mapLength / 2, mapWidth / 2, 2000)
let mapPlane = SCNNode()
mapPlane.position = SCNVector3(mapLength / 2, mapWidth / 2, 0)
mapPlane.geometry = SCNPlane(width: mapLength, height: mapWidth)
mapPlane.geometry?.firstMaterial?.diffuse.contents = UIColor.blackColor()
scene.rootNode.addChildNode(mapPlane)
mapPlane doesn't show at all! You have to rotate the camera to the underside of mapPlane in order to see it. You can easily fix this by adding a single line:
mapPlane.geometry?.firstMaterial?.cullMode = .Front
But I don't want to have to change the cullMode for every geometry/material. Is there a way to achieve this without requiring extra code at each geometry/material? Some transform that would invert the geometry face normals for all child nodes of rootNode? Ideally this would be achieved entirely by settings on the actual Scene, or by transforms on rootNode or the camera.
Related
How to create a line between two points in 3d space with RealityKit?
There are examples of creating lines between two points in Scenekit, however, there are basically none using RealityKit.
To create the line, I've created a rectangle model entity and placed it between my first touched point and the current touched point. From here, all I would need to do is rotate the rectangle to face the current touched point. However, using the simd_quatf(from: to:) doesn't work as intended.
rectangleModelEntity.transform.rotation = simd_quatf(from: firstTouchedPoint,
to: currTouchedPoint)
If I were to touch a point and then drag directly downwards, the rectangle model should be to be a straight line between first touched and current touched point, but it stays horizontal with a slight tilt.
To solve this, I tried getting the angle between my initially horzontal line as a vector and a vector from the first touched to current touched point
let startVec = currTouchedPoint - firstTouchedPoint
let endVec = endOfModelEntityPoint - modelEntityCenterPoint
let lengthVec = simd_length(cross(startVec, endVec))
let theta = atan2(lengthVec, dot(startVec, endVec))
This gives me the angle between two vectors in 3d space, which seems correct, when I checked it gave me 90 degrees when touching and dragging directly between it.
The problem is I don't know what the axis to rotate it on should be. Since this is 3d space, the line doesn't need to be on a 2d plane, the current touched position can be downwards and in front of the starting touch position.
rectangleModelEntity = simd_quatf(angle: theta, axis: ???)
Personally, I'm not even too sure if the above is the correct solution to creating a line between two points. In theory it's rather basic, create a rectangle with low height/depth to mimic a line, position it in the center of the starting and current touch point then rotate it so it's oriented correctly.
What should be the axis for the above degrees between two vectors?
Is there a better method of creating two lines between points in 3d space with RealityKit/ARKit?
I have implemented using a box. Let me know if you have a better way.
let midPosition = SIMD3(x:(position1.x + position2.x) / 2,
y:(position1.y + position2.y) / 2,
z:(position1.z + position2.z) / 2)
let anchor = AnchorEntity()
anchor.position = midPosition
anchor.look(at: position1, from: midPosition, relativeTo: nil)
let meters = simd_distance(position1, position2)
let lineMaterial = SimpleMaterial.init(color: .red,
roughness: 1,
isMetallic: false)
let bottomLineMesh = MeshResource.generateBox(width:0.025,
height: 0.025/2.5,
depth: meters)
let bottomLineEntity = ModelEntity(mesh: bottomLineMesh,
materials: [lineMaterial])
bottomLineEntity.position = .init(0, 0.025, 0)
anchor.addChild(bottomLineEntity)
The axis is the cross product of the direction your object is facing at the beginning and the direction it should be facing now.
Like if it's at position p1=[x1,y1,z1], initially facing d1=[0, 0, -1], and you want it to face a point p2=[x, y, z] the axis would be the cross product: |d1|✕|p2 - p1|.
May have to swap the two around, or just negate the angle though, depending on how it works out.
Ok, what I am trying to do is create physics body/colliding boundaries for my character, my SCNNode, in my SceneKit game Im building with ARKit. This is so my node cannot move out of the user's vision/go so far away that it isn't visible as it is currently doing. My SCNNode is moved by user input, so I need to make "world boundaries" while ARKit still doesn't have vertical wall detection
I know you can place an object some set distance ahead of you in the real world as stated here Understand coordinate spaces in ARKit
and I have done that with this, just making a box with physics body here -
let box = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0) //change to be VERY TALL - need to make it a giant room
node.physicsBody = SCNPhysicsBody(type: SCNPhysicsBodyType.static, shape: nil)
box.firstMaterial?.diffuse.contents = UIColor.red
box.firstMaterial?.isDoubleSided = true
node = SCNNode(geometry: box)
node.position = SCNVector3(view.pointOfView.simdWorldFront + float3(0, 0, -0.5)) //random distance ahead
And this works, and I could add it as a child node of camera so it moves as user moves, but I don't think Im doing this correctly.
Essentially I need 4 walls to box the user/SCNNode in (corral the character) that are infinitely high, and at the VERY edge of the horizontal plane that the user can see. Really I don't know what this distance should be in the x plane:
+ float3(0, 0, -0.5)
How would you create AR boundaries like this?
I'm not too great at math but what I am trying to accomplish is rotating my sprite to the direction of a vector impulse that is applied to it. My game is in 2D
If I tap below my sprite it goes upwards, if I tap below my sprite and to the right, it goes upwards and to the left, etc. etc.
I am doing this by just applying a normalized vector (unit vector?) impulse to my sprite which i got from the difference in position between the sprite and my tap.
let x = (ball.position.x - location.x)
let y = (ball.position.y - location.y)
let vectorLength = sqrt((x*x) + (y*y))
// Ignore constants
let unitVector = CGVector(dx: (x/vectorLength) * 25, dy: (y/vectorLength) * 50)
ball.physicsBody!.applyImpulse(unitVector)
Now what I would like to accomplish is the ability to rotate the sprite in the direction of that vector.
So for example if my sprite is traveling up and to the left at lets say a 45 degree angle, how can I rotate the sprite counterclockwise 45 degrees using the vector so that it appears to be facing the facing the direction its traveling?
something like sprite.zRotation = atan(unitVector.dy, unitVector.dx)?
So,
I have the exact position I want to place the node at. If I test things with a sphere geometry I can place spheres in the world by telling the node:
node.simdPosition = position
(I provide the "position" as an input to the function).
That successfully places the object in the world exactly where I want it to go.
What I really want to do is placing a plane:
let plane = SCNPlane(width: 0.2, height: 0.3)
plane.cornerRadius = plane.width / 10
plane.firstMaterial?.diffuse.contents = UIColor.red
plane.firstMaterial?.specular.contents = UIColor.white
let node = SCNNode(geometry: plane)
Then telling it to be placed at the "position":
node.simdPosition = position
All this works with the plane as well. What I have problems with is the angle:
I want to tell the plane's node to be placed with a given "angle" (around Y) offset to the camera. I tried this but it's not working:
node.rotation = SCNVector4Make(0, 1, 0, currentFrame.camera.eulerAngles.z - angle)
So then, the question is, how can a node be placed at a certain position and at the moment it gets placed in the world, also have a certain Y angle offset from the perpendicular to the camera?
I was using the wrong Euler angle... (z)
This made it work:
node.eulerAngles = SCNVector3Make(0, cameraEulerAngles.y - Float(0.7), 0)
I've been playing with the SCNNode object for a while now and I'm lost with the Pivot. How can I change the pivot of a SCNNode (SCNBox as a bar) and place the pivot on one of the edge of the bar?
A node's pivot is a transformation matrix, the inverse of which is applied to the node before its transform property takes effect. For example, take a look at this bit from the default SceneKit Game template in Xcode:
let boxNode = SCNNode()
boxNode.geometry = SCNBox(width: 1, height: 1, length: 1, chamferRadius: 0.02)
If you set the boxNode's position, that point corresponds to the center of the cube, and if you rotate it (as the template does in an animation), it spins around its center.
To change the anchor point, set the pivot to a translation transform:
boxNode.pivot = SCNMatrix4MakeTranslation(0.5, 0.5, 0.5)
Now, when you set the position that point corresponds to the top-right-front corner of the cube, and when you rotate the cube it spins around that corner.
More generally, a pivot transforms the contents of a node relative to the node's own transform. Suppose you wanted to model the precession of the Earth's axis of rotation. You could do this by creating two animations: one that animates pivot to spin the node around its own Y axis, and another that animates rotation to move that axis relative to the space containing the node.
On the pivot topic:
Just in case you do not have dimensions for your geometry/node something like this might help (especially for SCNText).
var minVec = SCNVector3Zero
var maxVec = SCNVector3Zero
if node.getBoundingBoxMin(&minVec, max: &maxVec) {
let bound = SCNVector3(x: maxVec.x + minVec.x,
y: maxVec.y + minVec.y,
z: maxVec.z + minVec.z)
node.pivot = SCNMatrix4MakeTranslation(bound.x / 2,
bound.y / 2,
bound.z / 2)
}