Three.js - 從UV座標計算三維座標

Question

我試圖將THREE.js中的一個對象的位置從平面2D座標（放置在2D圖像上的註釋）轉換爲3D座標，當圖像被包裹成3D形狀的紋理。這個想法是在等效的3D座標處放置一個小的3D對象來表示2D註釋。

我可以通過獲取與raycaster相交的對象的uv.x和uv.y屬性來做相反的操作，該屬性非常整潔。

以上是否可能在三？我需要能夠考慮不同的幾何形狀。

Answer 1

想通了：

既然你要查找的位置的UV座標：

首先，你需要在模型遞歸地通過每個三角形遍歷，傳遞從每個UV COORDS，並使用重心技術與臉部頂點UV陣列進行比較，以根據UV觀察該點是否存在於三角形內部。

一旦找到了正確的三角形，就可以找到三角形的相關頂點並將重心座標應用到它以獲得局部空間中的座標。

然後轉換爲世界空間。

代碼如下，有點粗糙和準備，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 []; 
    } 
};