swift - 如何在代码中创建 SceneKit SCNSkinner 对象？

Question

我有一个使用 SceneKit for iOS 8 的 Swift 应用程序。我从一个包含由骨架控制的网格的 .dae 文件加载场景。 在运行时，我需要修改纹理坐标。使用变换不是一种选择——我需要为网格中的每个顶点计算一个不同的、全新的 UV。

我知道 SceneKit 中的几何图形是不可变的，而且我读到建议的方法是手动制作副本。我正在尝试这样做，但在尝试在代码中重新创建 SCNSkinner 时，我总是以崩溃告终。崩溃是 C3DSourceAccessorGetMutableValuePtrAtIndex 中的 EXC_BAD_ACCESS。不幸的是，没有这方面的源代码，所以我不确定它为什么会崩溃。我已将其缩小到附加到网格节点的 SCNSkinner 对象。如果我不设置它，我就不会崩溃，并且一切正常。

编辑:这是一个更完整的崩溃调用堆栈:

C3DSourceAccessorGetMutableValuePtrAtIndex
C3DSkinPrepareMeshForGPUIfNeeded
C3DSkinnerMakeCurrentMesh
C3DSkinnerUpdateCurrentMesh
__CFSetApplyFunction_block_invoke
CFBasicHashApply
CFSetApplyFunction
C3DAppleEngineRenderScene
...

我没有找到任何关于如何手动创建 SCNSkinner 对象的文档或示例代码。因为我只是基于以前工作的网格创建它，所以应该不会太困难。我正在根据 Swift 文档创建 SCNSkinner，将所有正确的东西传递到 init.但是，SCNSkinner 中有一个骨架属性，我不确定如何设置。我将它设置为我正在复制的网格的原始 SCNSkinner 上的骨架，我认为 应该工作......但它没有。设置骨架属性时，它似乎没有分配。分配后立即检查它显示它仍然为零。作为测试，我尝试将原始网格的骨架属性设置为其他内容，并且在分配后它也保持不变。

任何人都可以阐明正在发生的事情吗？或者如何手动正确创建和设置 SCNSkinner 对象？

这是我用来手动克隆网格并将其替换为新网格的代码(我没有修改这里的任何源数据——我只是想确保我可以在以下位置创建一个副本这一点):

// This is at the start of the app, just so you can see how the scene is set up.
// I add the .dae contents into its own node in the scene. This seems to be the
// standard way to put multiple .dae models into the same scene. This doesn't seem to
// have any impact on the problem I'm having -- I've tried without this indirection
// and the same problem exists.
let scene = SCNScene()

let modelNode = SCNNode()
modelNode.name = "ModelNode"

scene.rootNode.addChildNode(modelNode)

let modelScene = SCNScene(named: "model.dae")

if modelScene != nil {
    if let childNodes = modelScene?.rootNode.childNodes {
        for childNode in childNodes {
            modelNode.addChildNode(childNode as SCNNode)
        }
    }
}


// This happens later in the app after a tap from the user.

let modelNode = scnView.scene!.rootNode.childNodeWithName("ModelNode", recursively: true)

let modelMesh = modelNode?.childNodeWithName("MeshName", recursively: true)

let verts = modelMesh?.geometry!.geometrySourcesForSemantic(SCNGeometrySourceSemanticVertex)
let normals = modelMesh?.geometry!.geometrySourcesForSemantic(SCNGeometrySourceSemanticNormal)
let texcoords = modelMesh?.geometry!.geometrySourcesForSemantic(SCNGeometrySourceSemanticTexcoord)
let boneWeights = modelMesh?.geometry!.geometrySourcesForSemantic(SCNGeometrySourceSemanticBoneWeights)
let boneIndices = modelMesh?.geometry!.geometrySourcesForSemantic(SCNGeometrySourceSemanticBoneIndices)
let geometry = modelMesh?.geometry!.geometryElementAtIndex(0)

// Note: the vertex and normal data is shared.
let vertsData = NSData(data: verts![0].data)
let texcoordsData = NSData(data: texcoords![0].data)
let boneWeightsData = NSData(data: boneWeights![0].data)
let boneIndicesData = NSData(data: boneIndices![0].data)
let geometryData = NSData(data: geometry!.data!)

let newVerts = SCNGeometrySource(data: vertsData, semantic: SCNGeometrySourceSemanticVertex, vectorCount: verts![0].vectorCount, floatComponents: verts![0].floatComponents, componentsPerVector: verts![0].componentsPerVector, bytesPerComponent: verts![0].bytesPerComponent, dataOffset: verts![0].dataOffset, dataStride: verts![0].dataStride)

let newNormals = SCNGeometrySource(data: vertsData, semantic: SCNGeometrySourceSemanticNormal, vectorCount: normals![0].vectorCount, floatComponents: normals![0].floatComponents, componentsPerVector: normals![0].componentsPerVector, bytesPerComponent: normals![0].bytesPerComponent, dataOffset: normals![0].dataOffset, dataStride: normals![0].dataStride)

let newTexcoords = SCNGeometrySource(data: texcoordsData, semantic: SCNGeometrySourceSemanticTexcoord, vectorCount: texcoords![0].vectorCount, floatComponents: texcoords![0].floatComponents, componentsPerVector: texcoords![0].componentsPerVector, bytesPerComponent: texcoords![0].bytesPerComponent, dataOffset: texcoords![0].dataOffset, dataStride: texcoords![0].dataStride)

let newBoneWeights = SCNGeometrySource(data: boneWeightsData, semantic: SCNGeometrySourceSemanticBoneWeights, vectorCount: boneWeights![0].vectorCount, floatComponents: boneWeights![0].floatComponents, componentsPerVector: boneWeights![0].componentsPerVector, bytesPerComponent: boneWeights![0].bytesPerComponent, dataOffset: boneWeights![0].dataOffset, dataStride: boneWeights![0].dataStride)

let newBoneIndices = SCNGeometrySource(data: boneIndicesData, semantic: SCNGeometrySourceSemanticBoneIndices, vectorCount: boneIndices![0].vectorCount, floatComponents: boneIndices![0].floatComponents, componentsPerVector: boneIndices![0].componentsPerVector, bytesPerComponent: boneIndices![0].bytesPerComponent, dataOffset: boneIndices![0].dataOffset, dataStride: boneIndices![0].dataStride)

let newGeometry = SCNGeometryElement(data: geometryData, primitiveType: geometry!.primitiveType, primitiveCount: geometry!.primitiveCount, bytesPerIndex: geometry!.bytesPerIndex)

let newMeshGeometry = SCNGeometry(sources: [newVerts, newNormals, newTexcoords, newBoneWeights, newBoneIndices], elements: [newGeometry])

newMeshGeometry.firstMaterial = modelMesh?.geometry!.firstMaterial

let newModelMesh = SCNNode(geometry: newMeshGeometry)

let bones = modelMesh?.skinner?.bones
let boneInverseBindTransforms = modelMesh?.skinner?.boneInverseBindTransforms
let skeleton = modelMesh!.skinner!.skeleton!
let baseGeometryBindTransform = modelMesh!.skinner!.baseGeometryBindTransform

newModelMesh.skinner = SCNSkinner(baseGeometry: newMeshGeometry, bones: bones, boneInverseBindTransforms: boneInverseBindTransforms, boneWeights: newBoneWeights, boneIndices: newBoneIndices)

newModelMesh.skinner?.baseGeometryBindTransform = baseGeometryBindTransform

// Before this assignment, newModelMesh.skinner?.skeleton is nil.
newModelMesh.skinner?.skeleton = skeleton
// After, it is still nil... however, skeleton itself is completely valid.

modelMesh?.removeFromParentNode()

newModelMesh.name = "MeshName"

let meshParentNode = modelNode?.childNodeWithName("MeshParentNode", recursively: true)

meshParentNode?.addChildNode(newModelMesh)

Answer 1

这三种方法可以帮助您找到解决方案:

1. SCNNode *hero = [SCNScene sceneNamed:@"Hero"].rootNode;
   SCNNode *hat = [SCNScene sceneNamed:@"FancyFedora"].rootNode;
   hat.skinner.skeleton = hero.skinner.skeleton;
   

2. [Export ("initWithFrame:")]
   public UIView (System.Drawing.RectangleF frame) : base (NSObjectFlag.Empty)
   {
   // Invoke the init method now.
       var initWithFrame = new Selector ("initWithFrame:").Handle;
       if (IsDirectBinding)
           Handle = ObjCRuntime.Messaging.IntPtr_objc_msgSend_RectangleF (this.Handle, initWithFrame, frame);
       else
           Handle = ObjCRuntime.Messaging.IntPtr_objc_msgSendSuper_RectangleF (this.SuperHandle, initWithFrame, frame);
   }
   

3. 参见 this link