如何在代码中创建 SceneKit SCNSkinner 对象？

我有一个在 iOS8上使用 SceneKit 的 Swift 应用程序。我从一个。包含由框架控制的网格的 dae 文件。在运行时，我需要修改纹理坐标。使用转换不是一个选项——我需要为网格中的每个顶点计算一个不同的、全新的 UV。

我知道几何图形在 SceneKit 中是不可变的，而且我读到建议的方法是手动复制。我正在尝试这样做，但是在尝试用代码重新创建 SCNSkinner时，我总是以崩溃告终。坠机是 C3DSourceAccessorGetMutableValuePtrAtIndex内部的 EXC_BAD_ACCESS。不幸的是，这个程序没有源代码，所以我不知道它为什么会崩溃。我已经把范围缩小到连接到网格节点的 SCNSkinner对象。如果我不设置，我不会得到一个崩溃，事情似乎是工作。

编辑: 这里有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。因为我只是创建它基于以前的工作网格，它应该不会太困难。我正在根据 Swift 文档创建 SCNSkinner，将所有正确的内容传递到 init 中。但是，在 SCNSkinner中有一个骨架属性，我不知道如何设置。我把它设置成我正在复制的网格的原始 SCNSkinner上的骨架应该有用... 但是没用。设置主干属性时，它似乎没有分配。在赋值之后立即检查它，表明它仍然为零。作为一个测试，我试图将原始网格的骨架属性设置为其他属性，并且在赋值之后，它也保持不变。

有人能解释一下发生了什么吗？或者如何正确地手动创建和设置 SCNSkinner对象？

下面是我用来手动克隆一个网格并用一个新网格替换它的代码(这里我没有修改任何源数据——我只是试图确保在这一点上可以创建一个副本) :

// 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)

5173

[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); }

小开

I don't specifically know what causes your code to crash but here is a way of generating a mesh, bones, and skinning that mesh -- all from code. Swift4 and iOS 12.

In the example, there is mesh representing the concatenation of two cylinders, with one of the cylinders branching off at a 45 degree angle, like so:

\
|

The cylinders are just extruded triangles, i.e., radialSegmentCount = 3. (Note that there are 12 vertices, not 9, since the two cylinders aren't really conjoined. The triangles are ordered like this:

      v5
^
v3 /__|__\ v1
|  |  |
|  v4 |
v2 |/___\| v0

There are 3 bones, corresponding to the heads and feet of the cylinders, where the middle bone corresponds to the head of the bottom cylinder and simultaneously the foot of the top cylinder. So for example, vertices v0, v2, and v4 correspond to bone0; v1, v3, v5 correspond to bone1, and so forth. That explains why boneIndices (see below) has the value that it does.

The resting positions of the bones corresponds to the resting positions of the cylinders in the geometry (bone2 sprouts off at a 45 degree angle from bone1, just like the cylinder geometry).

With that as context, the following code creates everything needed to skin the geometry:

let vertices = [float3(0.17841241, 0.0, 0.0), float3(0.17841241, 1.0, 0.0), float3(-0.089206174, 0.0, 0.1545097), float3(-0.089206174, 1.0, 0.1545097), float3(-0.089206256, 0.0, -0.15450965), float3(-0.089206256, 1.0, -0.15450965), float3(0.12615661, 1.1261566, 0.0), float3(-0.58094996, 1.8332633, 0.0), float3(-0.063078284, 0.9369217, 0.1545097), float3(-0.7701849, 1.6440284, 0.1545097), float3(-0.063078344, 0.93692166, -0.15450965), float3(-0.77018493, 1.6440284, -0.15450965)]
let indices: [UInt8] = [0, 1, 2, 3, 4, 5, 0, 1, 1, 6, 6, 7, 8, 9, 10, 11, 6, 7]
let geometrySource = SCNGeometrySource(vertices: vertices.map { SCNVector3($0) })
let geometryElement = SCNGeometryElement(indices: indices, primitiveType: .triangleStrip)
let geometry = SCNGeometry(sources: [geometrySource], elements: [geometryElement])


let bone0 = SCNNode()
bone0.simdPosition = float3(0,0,0)
let bone1 = SCNNode()
bone1.simdPosition = float3(0,1,0)
let bone2 = SCNNode()
bone2.simdPosition = float3(0,1,0) + normalize(float3(-1,1,0))
let bones = [bone0, bone1, bone2]


let boneInverseBindTransforms: [NSValue]? = bones.map { NSValue(scnMatrix4: SCNMatrix4Invert($0.transform)) }
var boneWeights: [Float] = vertices.map { _ in 1.0 }
var boneIndices: [UInt8] = [
0, 1, 0, 1, 0, 1,
1, 2, 1, 2, 1, 2,
]


let boneWeightsData = Data(bytesNoCopy: &boneWeights, count: boneWeights.count * MemoryLayout<Float>.size, deallocator: .none)
let boneIndicesData = Data(bytesNoCopy: &boneIndices, count: boneWeights.count * MemoryLayout<UInt8>.size, deallocator: .none)


let boneWeightsGeometrySource = SCNGeometrySource(data: boneWeightsData, semantic: .boneWeights, vectorCount: boneWeights.count, usesFloatComponents: true, componentsPerVector: 1, bytesPerComponent: MemoryLayout<Float>.size, dataOffset: 0, dataStride: MemoryLayout<Float>.size)
let boneIndicesGeometrySource = SCNGeometrySource(data: boneIndicesData, semantic: .boneIndices, vectorCount: boneIndices.count, usesFloatComponents: false, componentsPerVector: 1, bytesPerComponent: MemoryLayout<UInt8>.size, dataOffset: 0, dataStride: MemoryLayout<UInt8>.size)


let skinner = SCNSkinner(baseGeometry: geometry, bones: bones, boneInverseBindTransforms: boneInverseBindTransforms, boneWeights: boneWeightsGeometrySource, boneIndices: boneIndicesGeometrySource)


let node = SCNNode(geometry: geometry)
node.skinner = skinner

Note: In most cases, you should use UInt16 not UInt8.