Volume Grid Isosurface mesh issue

从 src/volume_grid_scalar_quantity.cpp 开始，检查 createIsosurfaceProgram() 和 registerIsosurfaceAsMesh()，其中展示了 MarchingCube 调用和坐标变换。将两条路径中的网格维度顺序与体积缓冲区布局进行比较。当 volume-grid 等值面在两种用法中都以正确的方向和单元顺序渲染时，即表示完成。

Hi,

I've run into an issue with the isosurface generation for volume grid scalar quantities. The problem appears to be that the change made to fix the frame transformation for #253 wasn't propagated into the grid dimensions passed to the MarchingCube library, resulting in the grid cells being interpreted in the wrong order.

The following shows a volume grid of the Stanford Bunny and its isosurface visualization with the 2.2.1 release:

By swizzling the grid dimensions passed into MarchingCube we get the following (correct) result instead:

The patch for the above fix is:

diff --git a/src/volume_grid_scalar_quantity.cpp b/src/volume_grid_scalar_quantity.cpp                                 
index cde441a..603841f 100644                                                                                          
--- a/src/volume_grid_scalar_quantity.cpp                                                                              
+++ b/src/volume_grid_scalar_quantity.cpp                                                                              
@@ -165,8 +165,8 @@ void VolumeGridNodeScalarQuantity::createIsosurfaceProgram() {                                     
                                                                                                                       
   // Extract the isosurface from the level set of the scalar field                                                    
   MC::mcMesh isosurfaceMesh;                                                                                          
-  MC::marching_cube(&values.data.front(), isosurfaceLevel.get(), parent.getGridNodeDim().x, parent.getGridNodeDim().y,
-                    parent.getGridNodeDim().z, isosurfaceMesh);                                                       
+  MC::marching_cube(&values.data.front(), isosurfaceLevel.get(), parent.getGridNodeDim().z, parent.getGridNodeDim().y,
+                    parent.getGridNodeDim().x, isosurfaceMesh);                                                       
                                                                                                                       
   // Transform the result to be aligned with our volume's spatial layout                                              
   glm::vec3 scale = parent.gridSpacing();                                                                             
@@ -215,8 +215,8 @@ SurfaceMesh* VolumeGridNodeScalarQuantity::registerIsosurfaceAsMesh(std::string                    
                                                                                                                       
   // extract the mesh                                                                                                 
   MC::mcMesh isosurfaceMesh;                                                                                          
-  MC::marching_cube(&values.data.front(), isosurfaceLevel.get(), parent.getGridNodeDim().x, parent.getGridNodeDim().y,
-                    parent.getGridNodeDim().z, isosurfaceMesh);                                                       
+  MC::marching_cube(&values.data.front(), isosurfaceLevel.get(), parent.getGridNodeDim().z, parent.getGridNodeDim().y,
+                    parent.getGridNodeDim().x, isosurfaceMesh);                                                       
   glm::vec3 scale = parent.gridSpacing();                                                                             
   for (auto& p : isosurfaceMesh.vertices) {                                                                           
     // swizzle to account for change of coordinate/buffer ordering in the MC lib                                      

I'm not sure how you prefer to manage the repo, but if you'd like me to open a PR for the fix I'm happy to. Thanks!