javascript – 将Three.js场景导出到STL,保持动画完好无损

不幸的是,答案是无处可去的.这些都是在GPU上通过传入几个大型数组调用WebGL函数来计算的.

为了解释如何计算这个,我们首先回顾一下动画是如何工作的,使用this knight example作为参考.
SkinnedMesh对象包含一个骨架(由许多Bone组成)和一堆顶点.它们从所谓的@L_450_4@开始排列.每个顶点绑定到0-4个骨骼,如果这些骨骼移动,顶点将移动,创建动画.

如果您采取我们的骑士示例,暂停动画中摆,并尝试standard STL exporter,生成的STL文件将完全是这个姿势,而不是动画.为什么？因为它只是查看mesh.geometry.vertices,它在动画期间不会从原始绑定姿势更改.只有骨骼会发生变化,GPU会进行一些数学运算来移动与每个骨骼相对应的顶点.

移动每个顶点的数学运算非常简单 – 在导出之前将绑定姿势顶点位置转换为骨骼空间,然后从骨骼空间转换为全局空间.
调整here的代码,我们将其添加到原始导出器：

vector.copy( vertices[ vertexIndex ] );
boneInDices = [];   //which bones we need
boneInDices[0] = mesh.geometry.skinInDices[vertexIndex].x;
boneInDices[1] = mesh.geometry.skinInDices[vertexIndex].y;
boneInDices[2] = mesh.geometry.skinInDices[vertexIndex].z;
boneInDices[3] = mesh.geometry.skinInDices[vertexIndex].w;

weights = [];   //some bones impact the vertex more than others
weights[0] = mesh.geometry.skinWeights[vertexIndex].x;
weights[1] = mesh.geometry.skinWeights[vertexIndex].y;
weights[2] = mesh.geometry.skinWeights[vertexIndex].z;
weights[3] = mesh.geometry.skinWeights[vertexIndex].w;

inverses = [];  //boneInverses are the transform from bind-pose to some "bone space"
inverses[0] = mesh.skeleton.boneInverses[ boneInDices[0] ];
inverses[1] = mesh.skeleton.boneInverses[ boneInDices[1] ];
inverses[2] = mesh.skeleton.boneInverses[ boneInDices[2] ];
inverses[3] = mesh.skeleton.boneInverses[ boneInDices[3] ];

skinMatrices = [];  //each bone's matrix world is the transform from "bone space" to the "global space"
skinMatrices[0] = mesh.skeleton.bones[ boneInDices[0] ].matrixWorld;
skinMatrices[1] = mesh.skeleton.bones[ boneInDices[1] ].matrixWorld;
skinMatrices[2] = mesh.skeleton.bones[ boneInDices[2] ].matrixWorld;
skinMatrices[3] = mesh.skeleton.bones[ boneInDices[3] ].matrixWorld;

var finalVector = new THREE.Vector4();
for(var k = 0; k<4; k++) {
    var tempVector = new THREE.Vector4(vector.x,vector.y,vector.z);
    //weight the transformation
    tempVector.multiplyScalar(weights[k]);
    //the inverse takes the vector into local bone space
    tempVector.applymatrix4(inverses[k])
    //which is then transformed to the appropriate world space
    .applymatrix4(skinMatrices[k]);
    finalVector.add(tempVector);
}

output += '\t\t\tvertex ' + finalVector.x + ' ' + finalVector.y + ' ' + finalVector.z + '\n';

这会产生如下所示的STL文件：

完整代码可在https://gist.github.com/kjlubick/fb6ba9c51df63ba0951f获得