Three.js - 从UV坐标计算三维坐标

Question

我试图将THREE.js中的一个对象的位置从平面2D坐标（放置在2D图像上的注释）转换为3D坐标，当图像被包裹成3D形状的纹理。这个想法是在等效的3D坐标处放置一个小的3D对象来表示2D注释。

我可以通过获取与raycaster相交的对象的uv.x和uv.y属性来做相反的操作，该属性非常整洁。

以上是否可能在三？我需要能够考虑不同的几何形状。

Answer 1

想通了：

既然你要查找的位置的UV坐标：

首先，你需要在模型递归地通过每个三角形遍历，传递从每个UV COORDS，并使用重心技术与脸部顶点UV阵列进行比较，以根据UV观察该点是否存在于三角形内部。

一旦找到了正确的三角形，就可以找到三角形的相关顶点并将重心坐标应用到它以获得局部空间中的坐标。

然后转换为世界空间。

代码如下，有点粗糙和准备，但你的想法：

// Recursively traverse through the model. 
var traversePolygonsForGeometries = function (node, uvx, uvy) { 
if (node.geometry) { 
    // Return a list of triangles that have the point within them. 
    // The returned objects will have the x,y,z barycentric coordinates of the point inside the respective triangle 
    var baryData = annotationTest(uvx, uvy, node.geometry.faceVertexUvs); 
    if (baryData.length) { 
     for (var j = 0; j < baryData.length; j++) { 
      // In my case I only want to return materials with certain names. 
      if (node.geometry.faces[baryData[j][0]].daeMaterial === 
       "frontMaterial" || node.geometry.faces[baryData[j][0]].daeMaterial === 
       "print_area1_0" 
       ) { 
       // Find the vertices corresponding to the triangle in the model 
       var vertexa = node.geometry.vertices[node.geometry.faces[baryData[j][0]].a]; 
       var vertexb = node.geometry.vertices[node.geometry.faces[baryData[j][0]].b]; 
       var vertexc = node.geometry.vertices[node.geometry.faces[baryData[j][0]].c]; 
       // Sum the barycentric coordinates and apply to the vertices to get the coordinate in local space 
       var worldX = vertexa.x * baryData[j][1] + vertexb.x * baryData[j][2] + vertexc.x * baryData[j][3]; 
       var worldY = vertexa.y * baryData[j][1] + vertexb.y * baryData[j][2] + vertexc.y * baryData[j][3]; 
       var worldZ = vertexa.z * baryData[j][1] + vertexb.z * baryData[j][2] + vertexc.z * baryData[j][3]; 
       var vector = new THREE.Vector3(worldX, worldY, worldZ); 
       // Translate to world space 
       var worldVector = vector.applyMatrix4(node.matrixWorld); 
       return worldVector; 
      } 
     } 
    } 
} 
if (node.children) { 
    for (var i = 0; i < node.children.length; i++) { 
     var worldVectorPoint = traversePolygonsForGeometries(node.children[i], uvx, uvy); 
     if (worldVectorPoint) return worldVectorPoint; 
    } 
} 
}; 

// Loops through each face vertex UV item and tests if it is within the triangle. 
function annotationTest(uvX, uvY, faceVertexUvArray) { 
    var point = {}; 
    point.x = uvX; 
    point.y = uvY; 
    var results = []; 
    for (i = 0; i < faceVertexUvArray[0].length; i++) { 
     var result = ptInTriangle(point, faceVertexUvArray[0][i][0], faceVertexUvArray[0][i][1], faceVertexUvArray[0][i][2]); 
     if (result.length) { 
      results.push([i, result[0], result[1], result[2]]); 
     } 
    } 
    return results; 
}; 

// This is a standard barycentric coordinate function. 
function ptInTriangle(p, p0, p1, p2) { 
    var x0 = p.x; 
    var y0 = p.y; 
    var x1 = p0.x; 
    var y1 = p0.y; 
    var x2 = p1.x; 
    var y2 = p1.y; 
    var x3 = p2.x; 
    var y3 = p2.y; 

    var b0 = (x2 - x1) * (y3 - y1) - (x3 - x1) * (y2 - y1) 
    var b1 = ((x2 - x0) * (y3 - y0) - (x3 - x0) * (y2 - y0))/b0 
    var b2 = ((x3 - x0) * (y1 - y0) - (x1 - x0) * (y3 - y0))/b0 
    var b3 = ((x1 - x0) * (y2 - y0) - (x2 - x0) * (y1 - y0))/b0 

    if (b1 > 0 && b2 > 0 && b3 > 0) { 
     return [b1, b2, b3]; 
    } else { 
     return []; 
    } 
};