ios - 在SceneKit上画一条线在设备上不起作用

按照以下解决方案：Custom SceneKit Geometry并转换为Swift 3，代码变为：

func drawLine() {

    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: [CInt] = [0, 1, 2]

    let dat  = NSData(
        bytes: indexes,
        length: MemoryLayout<CInt>.size * indexes.count
    )
    let ele = SCNGeometryElement(
        data: dat as Data,
        primitiveType: .line,
        primitiveCount: 2,
        bytesPerIndex: MemoryLayout<CInt>.size
    )
    let geo = SCNGeometry(sources: [src], elements: [ele])

    let nd = SCNNode(geometry: geo)

    geo.materials.first?.lightingModel = .blinn
    geo.materials.first?.diffuse.contents = UIColor.red
    scene.rootNode.addChildNode(nd)

}

它可以在模拟器上运行：



但是我在设备上出现错误：

/BuildRoot/Library/Caches/com.apple.xbs/Sources/Metal/Metal-85.83/ToolsLayers/Debug/MTLDebugRenderCommandEncoder.mm:130: failed assertion `indexBufferOffset(0) + (indexCount(4) * 4) must be <= [indexBuffer length](12).'

怎么了？

整个代码在这里：Source code

最佳答案

我正在回答自己的问题，因为我找到了可以帮助他人的解决方案。

问题出在“索引”上，3个索引不会绘制2个顶点。必须为要绘制的每个顶点设置2个索引。

这是最终功能：

func drawLine(_ verts : [SCNVector3], color : UIColor) -> SCNNode? {

    if verts.count < 2 { return nil }

    let src = SCNGeometrySource(vertices: verts, count: verts.count )
    var indexes: [CInt] = []

    for i in 0...verts.count - 1 {
        indexes.append(contentsOf: [CInt(i), CInt(i + 1)])
    }

    let dat  = NSData(
        bytes: indexes,
        length: MemoryLayout<CInt>.size * indexes.count
    )

    let ele = SCNGeometryElement(
        data: dat as Data,
        primitiveType: .line,
        primitiveCount: verts.count - 1,
        bytesPerIndex: MemoryLayout<CInt>.size
    )

    let line = SCNGeometry(sources: [src], elements: [ele])

    let node = SCNNode(geometry: line)

    line.materials.first?.lightingModel = .blinn
    line.materials.first?.diffuse.contents = color

    return node
}

致电：

scene.rootNode.addChildNode(
    drawLine(
        [SCNVector3(x: -1,y: 0,z: 0),
         SCNVector3(x: 1,y: 0.5,z: 1),
         SCNVector3(x: 0,y: 1.5,z: 0)] , color: UIColor.red
        )!
)

将得出：