iOS上Swift中的自定义SceneKit Geometry无法正常工作但是等效的Objective C代码可以 [英] Custom SceneKit Geometry in Swift on iOS not working but equivalent Objective C code does

问题描述

我很想采用新的Swift语言，因为这似乎是Apple开发的前进方向。我对iOS 8中的新SceneKit支持印象深刻。我想在运行时以编程方式创建自定义几何，但我很难让Swift代码工作。然而，Objective C中的等效代码工作正常。

I am keen to adopt the new Swift language as this seems to be the way forward with Apple development. I have also been impressed with the new SceneKit support in iOS 8. I would like to programatically create custom geometry at runtime but I am struggling to get the Swift code to work. Yet the equivalent code in Objective C works OK.

这可能是一个错误，或者我做错了什么。

This could be a bug, or something I am doing wrong.

我只是想创建并渲染一个三角形。为简单起见，此时我将忽略法线和纹理等。所以我只期待看到黑色三角形。

I am simply trying to create and render a single triangle. I will ignore the normals and textures etc at this point for simplicity. So I am only expecting to see a black triangle.

Swift Code（不工作）

Swift Code (not working)

var verts = [SCNVector3(x: 0,y: 0,z: 0),SCNVector3(x: 1,y: 0,z: 0),SCNVector3(x: 0,y: 1,z: 0)]

let src = SCNGeometrySource(vertices: &verts, count: 3)
let indexes:Int[]=[0,1,2]
let dat  = NSData(bytes: indexes, length: sizeofValue(indexes))
let ele = SCNGeometryElement(data:dat, primitiveType: .Triangles, primitiveCount: 1, bytesPerIndex: sizeof(Int))
let geo = SCNGeometry(sources: [src], elements: [ele])

let nd = SCNNode(geometry: geo)
scene.rootNode.addChildNode(nd)

目标C代码（确实有效）

Objective C Code (which does work)

SCNVector3 verts[] = { SCNVector3Make(0, 0, 0), SCNVector3Make(1, 0, 0), SCNVector3Make(0, 1, 0) };
SCNGeometrySource *src = [SCNGeometrySource geometrySourceWithVertices:verts count:3];

int indexes[] = { 0, 1, 2 };
NSData *datIndexes = [NSData dataWithBytes:indexes length:sizeof(indexes)];
SCNGeometryElement *ele = [SCNGeometryElement geometryElementWithData:datIndexes primitiveType:SCNGeometryPrimitiveTypeTriangles primitiveCount:1 bytesPerIndex:sizeof(int)];
SCNGeometry *geo = [SCNGeometry geometryWithSources:@[src] elements:@[ele]];

SCNNode *nd = [SCNNode nodeWithGeometry:geo];
d
[scene.rootNode addChildNode:nd];

任何指针都会受到赞赏。

Any pointers would be appreciated.

推荐答案

嗯，这两段代码并没有将完全转换为彼此。 C中的 int 与Swift中的 Int 不同。它在Swift中实际上被称为 CInt ：

Well, the two pieces of code doesn't translate exactly to one another. The int in C is not the same as Int in Swift. It's actually called CInt in Swift:

/// The C 'int' type.
typealias CInt = Int32

如果您更改两次出现以使用 CInt 相反，你之前得到的错误信息消失了（至少对我来说是OS X Playground。但是，它仍然没有为我渲染任何东西。

If you change both occurrences to use CInt instead, the error message that you previously got goes away (at least for me in an OS X Playground. However, it still doesn't render anything for me.

我不认为 sizeofValue 用于返回数组的大小。它看起来像它返回指针的大小：

I don't think sizeofValue is used to return the size of an array. It looks to me like it's returning the size of the pointer:

let indexes: CInt[] = [0, 1, 2]
sizeofValue(indexes)                   // is 8
sizeof(CInt)                           // is 4
sizeof(CInt) * countElements(indexes)  // is 12

// compare to other CInt[]
let empty: CInt[] = []
let large: CInt[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

sizeofValue(indexes)                   // is 8 (your array of indices again)
sizeofValue(empty)                     // is 8
sizeofValue(large)                     // is 8

所以，对我来说，下面的代码是有效的（我已经将参数放在不同的行上，以便更容易指出我的更改）：

So, for me the following code works (I've put the arguments on different lines to make it easier to point out my changes):

let src = SCNGeometrySource(vertices: &verts, count: 3)
let indexes: CInt[] = [0, 1, 2] // Changed to CInt

let dat  = NSData(
    bytes: indexes,
    length: sizeof(CInt) * countElements(indexes) // Changed to size of CInt * count
)
let ele = SCNGeometryElement(
    data: dat,
    primitiveType: .Triangles,
    primitiveCount: 1,
    bytesPerIndex: sizeof(CInt) // Changed to CInt
)
let geo = SCNGeometry(sources: [src], elements: [ele])

let nd = SCNNode(geometry: geo)
scene.rootNode.addChildNode(nd)

结果如下：

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