ios - 获取 3D 模型的高度及其转换后的屏幕坐标

Question

我正在使用 ARKit 渲染 Collada (*.dae) 文件。作为我的 ARSCNView 的叠加层，我添加了一个 SKScene，它只显示一个消息气泡(还没有文本)。

目前，我知道如何修改气泡的位置，使它看起来总是在我的 3D 模型的脚下。我这样做:

func renderer(_ renderer: SCNSceneRenderer, didRenderScene scene: SCNScene, atTime time: TimeInterval)  {
    if let overlay = sceneView.overlaySKScene as? BubbleMessageScene {            
        guard let borisNode = sceneView.scene.rootNode.childNode(withName: "boris", recursively: true) else { return }

        let boxWorldCoordinates = sceneView.scene.rootNode.convertPosition(borisNode.position, from:sceneView.scene.rootNode.parent)
        let screenCoordinates = self.sceneView.projectPoint(boxWorldCoordinates)
        let boxY = overlay.size.height - CGFloat(screenCoordinates.y)

        overlay.bubbleNode?.position.x = CGFloat(screenCoordinates.x) - (overlay.bubbleNode?.size.width)!/2
        overlay.bubbleNode?.position.y = boxY
    }
}

但是我的泡泡总是在 3D 模型的脚，因为我只能获得我模型的 SCNNode 位置，它被锚定在那里。我希望它位于我的模型的头部。

有没有一种方法可以获得我的 3D 模型的高度，然后是它转换后的屏幕坐标，这样无论我拿着手机在哪里，气泡信息看起来总是在头部旁边？

Answer 1

每个 SCNNode 都有一个 boundingBox 属性，它是:

The minimum and maximum corner points of the object’s bounding box.

那么这意味着:

Scene Kit defines a bounding box in the local coordinate space using two points identifying its corners, which implicitly determine six axis-aligned planes marking its limits. For example, if a geometry’s bounding box has the minimum corner {-1, 0, 2} and the maximum corner {3, 4, 5}, all points in the geometry’s vertex data have an x-coordinate value between -1.0 and 3.0, inclusive.

如果您在 SceneKit Editor 中查看，您还可以看到以米为单位的模型大小(我说这只是作为您可以引用以检查计算的一个点):

在我的示例中，我使用的是上述尺寸的口袋妖怪模型。

我缩放了模型(您可能也这样做了)例如:

 pokemonModel.scale = SCNVector3(0.01, 0.01, 0.01)

所以为了得到 SCNNode 的 boundingBox 我们可以这样做:

/// Returns The Original Width & Height Of An SCNNode
///
/// - Parameter node: SCNNode
func getSizeOfModel(_ node: SCNNode){

     //1. Get The Size Of The Node Without Scale
     let (minVec, maxVec) = node.boundingBox
     let unScaledHeight = maxVec.y - minVec.y
     let unScaledWidth = maxVec.x - minVec.x

     print("""
         UnScaled Height = \(unScaledHeight)
         UnScaled Width = \(unScaledWidth)
           """)
    }

这样调用:

 getSizeOfModel(pokemonModel)

当然，既然我们的 SCNNode 已经缩放，这并没有多大帮助，所以显然我们需要通过重写函数来考虑到这一点:

/// Returns The Original & Scaled With & Height On An SCNNode
///
/// - Parameters:
///   - node: SCNode
///   - scalar: Float
func getOriginalAndScaledSizeOfNode(_ node: SCNNode, scalar: Float){

     //1. Get The Size Of The Node Without Scale
     let (minVec, maxVec) = node.boundingBox
     let unScaledHeight = maxVec.y - minVec.y
     let unScaledWidth = maxVec.x - minVec.x

     print("""
         UnScaled Height = \(unScaledHeight)
         UnScaled Width = \(unScaledWidth)
         """)


     //2. Get The Size Of The Node With Scale
     let max = node.boundingBox.max
     let maxScale = SCNVector3(max.x * scalar, max.y * scalar, max.z * scalar)

     let min = node.boundingBox.min
     let minScale = SCNVector3(min.x * scalar, min.y * scalar, min.z * scalar)

     let heightOfNodeScaled = maxScale.y - minScale.y
     let widthOfNodeScaled = maxScale.x - minScale.x

     print("""
         Scaled Height = \(heightOfNodeScaled)
         Scaled Width = \(widthOfNodeScaled)
         """)

}

这样调用:

 getOriginalAndScaledSizeOfNode(pokemonModel, scalar: 0.01)

完成此操作后，你说你想在模型上方放置一个“气泡”，然后可以这样做:

func getSizeOfNodeAndPositionBubble(_ node: SCNNode, scalar: Float){

     //1. Get The Size Of The Node Without Scale
     let (minVec, maxVec) = node.boundingBox
     let unScaledHeight = maxVec.y - minVec.y
     let unScaledWidth = maxVec.x - minVec.x

     print("""
         UnScaled Height = \(unScaledHeight)
         UnScaled Width = \(unScaledWidth)
         """)

     //2. Get The Size Of The Node With Scale
     let max = node.boundingBox.max
     let maxScale = SCNVector3(max.x * scalar, max.y * scalar, max.z * scalar)

     let min = node.boundingBox.min
     let minScale = SCNVector3(min.x * scalar, min.y * scalar, min.z * scalar)

     let heightOfNodeScaled = maxScale.y - minScale.y
     let widthOfNodeScaled = maxScale.x - minScale.x

     print("""
         Scaled Height = \(heightOfNodeScaled)
         Scaled Width = \(widthOfNodeScaled)
         """)

     //3. Create A Buubble
     let pointNodeHolder = SCNNode()
     let pointGeometry = SCNSphere(radius: 0.04)
     pointGeometry.firstMaterial?.diffuse.contents = UIColor.cyan
     pointNodeHolder.geometry = pointGeometry

     //4. Place The Bubble At The Origin Of The Model, At The Models Origin + It's Height & At The Z Position

     pointNodeHolder.position = SCNVector3(node.position.x, node.position.y + heightOfNodeScaled, node.position.z)
          self.augmentedRealityView.scene.rootNode.addChildNode(pointNodeHolder)

}

这会产生以下结果(我也在其他一些不幸的 Pokemon 上测试过):

您可能还想在计算中添加一些“填充”，以便节点比模型顶部高一点，例如:

 pointNodeHolder.position = SCNVector3(node.position.x, node.position.y + heightOfNodeScaled + 0.1, node.position.z) 

我的数学不是很好，这使用 SCNNode 作为气泡而不是 SKScene，但希望它能为您指明正确的方向...