ios - 显示拉伸(stretch) Material 应用于 SCNGeometrySource 节点

Question

我使用 SCNGeometrySource 使用自定义选择的 SCNVector3 点创建了 SCNNode，并应用图像 Material 来显示非常拉伸(stretch)的 Material 。如何在 SCNGeometrySource 节点上正确应用 Material 。

func getsquareDrawnLineFrom(pos1: SCNVector3,
                            pos2: SCNVector3,
                            pos3: SCNVector3) -> SCNNode {

    let square = SquareplanlineFrom(vector1: pos1, vector2: pos2, vector3: pos3)
    //SCNGeometrySource.Semantic.texcoord
    //SCNGeometrySource.Semantic.normal
    let material = SCNMaterial()
    // material.diffuse.contents = UIColor.lightGray
    material.diffuse.contents = UIImage(named: "grid")
    material.diffuse.contentsTransform = SCNMatrix4MakeScale(32, 32, 0)
    material.diffuse.wrapS = .repeat
    material.diffuse.wrapT = .repeat
    square.materials = [material]
    let square1 = SCNNode(geometry: square)
    square1.name = "tringle"
    return square1
}

// get line geometry between two vectors
func SquareplanlineFrom(vector1: SCNVector3,
              vector2: SCNVector3, vector3: SCNVector3) -> SCNGeometry {
     let normalsPerFace = 3
    let indices: [Int32] = [0, 1, 2]
    let source = SCNGeometrySource(vertices: [vector1, vector2, vector3])
    let normals:[SCNVector3] = [
        vector1,
        vector2,
        vector3].map{[SCNVector3](repeating:$0,count:normalsPerFace)}.flatMap{$0}
    let normalSource = SCNGeometrySource(normals: normals)
    let cgp1 = CGPoint(x: CGFloat(vector1.x), y: CGFloat(vector1.y))
    let cgp2 = CGPoint(x: CGFloat(vector2.x), y: CGFloat(vector2.y))
    let cgp3 = CGPoint(x: CGFloat(vector3.x), y: CGFloat(vector3.y))
    let textcoord = SCNGeometrySource(textureCoordinates: [cgp1,cgp2,cgp3])

    // let texcoord = SCNGeometrySource(textureCoordinates: [])
    // let normalSource = SCNGeometrySource(normals: [vector1, vector2, vector3])

    let element = SCNGeometryElement(indices: indices,
                                     primitiveType: .triangles)
    return SCNGeometry(sources: [source,normalSource,textcoord], elements: [element])
}

Answer 1

纹理的比例问题:

我不知道你的模型的大小，但我认为问题是——你增加了一个比例，尽管你必须减少它才能正确映射纹理。

My texture's size is 2K square (2048x2048, 72dpi).

这是一段代码(我这里使用的是macOS版本):

internal func getFaceDrawnFrom(pos1: SCNVector3,
                               pos2: SCNVector3,
                               pos3: SCNVector3) -> SCNNode {

    let triGeo = generateGeoFrom(vector1: pos1,
                                 vector2: pos2,
                                 vector3: pos3)

    let material = SCNMaterial()
    material.diffuse.contents = NSImage.Name("art.scnassets/jaguar.jpg")

    // your scale
    // material.diffuse.contentsTransform = SCNMatrix4MakeScale(32, 32, 0)

    material.isDoubleSided = true

    material.diffuse.contentsTransform = .init(
                                     m11: 0.05, m12: 0,    m13: 0,    m14: 0,
                                     m21: 0,    m22: 0.05, m23: 0,    m24: 0,
                                     m31: 0,    m32: 0,    m33: 1,    m34: 0,
                                     m41: 0,    m42: 0,    m43: 0,    m44: 1)
    material.diffuse.wrapS = .repeat
    material.diffuse.wrapT = .repeat
    square.materials = [material]

    let node = SCNNode(geometry: triGeo)
    node.name = "triangularFace"
    scene.rootNode.addChildNode(node)
    return node
}

然后:

fileprivate func generateGeoFrom(vector1: SCNVector3,
                                 vector2: SCNVector3,
                                 vector3: SCNVector3) -> SCNGeometry {

    let normalsPerFace = 3
    let indices: [Int32] = [0, 1, 2]
    let source = SCNGeometrySource(vertices: [vector1, vector2, vector3])

    let vecs = [vector1, vector2, vector3].map { 
        [SCNVector3](repeating: $0, count: normalsPerFace) 
    }.flatMap { $0 }

    let normals: [SCNVector3] = vecs

    let normalSource = SCNGeometrySource(normals: normals)
    let cgp1 = CGPoint(x: CGFloat(vector1.x), y: CGFloat(vector1.y))
    let cgp2 = CGPoint(x: CGFloat(vector2.x), y: CGFloat(vector2.y))
    let cgp3 = CGPoint(x: CGFloat(vector3.x), y: CGFloat(vector3.y))
    let textcoord = SCNGeometrySource(textureCoordinates: [cgp1, cgp2, cgp3])
        
    let element = SCNGeometryElement(indices: indices,
                               primitiveType: .triangles)

    return SCNGeometry(sources: [source, normalSource, textcoord], 
                      elements: [element])
}

然后我们调用这个方法。

let instance = getFaceDrawnFrom(pos1: SCNVector3(x: 0, y: 0, z: 0),
                                pos2: SCNVector3(x: 8, y: 5, z: 0),
                                pos3: SCNVector3(x:-8, y: 5, z: 0))

法线方向问题

通常，模型的每个三角形面都有 3 条法线，换句话说，每个面的每个顶点都有一条法线。法线必须垂直于表面，而不是平行。如果您遇到表面法线问题，那么您将无法照亮模型。