如何使用Nvidia Physx 4.1烘焙FBX网格？含凹、凸网格处理方法

一、环境准备 #

• 配置好Assimp（包含头文件、链接库）与PhysX 4.1（包含PhysX、PhysXCooking等模块的头文件及库）
• 项目中引入必要头文件：

  #include <assimp/Importer.hpp>
  #include <assimp/scene.h>
  #include <assimp/postprocess.h>
  #include <PxPhysicsAPI.h>
  

• 初始化PhysX核心环境：

  physx::PxFoundation* foundation = PxCreateFoundation(PX_PHYSICS_VERSION, gDefaultAllocatorCallback, gDefaultErrorCallback);
  physx::PxPhysics* physics = PxCreatePhysics(PX_PHYSICS_VERSION, *foundation, physx::PxTolerancesScale(), true);
  physx::PxCooking* cooking = PxCreateCooking(PX_PHYSICS_VERSION, *foundation, physx::PxCookingParams(physx::PxTolerancesScale()));
  

二、用Assimp加载FBX文件 #

编写通用加载函数，提取网格的顶点、索引数据：

bool loadFBXMesh(const std::string& filePath, std::vector<physx::PxVec3>& vertices, std::vector<physx::PxU32>& indices) {
    Assimp::Importer importer;
    const aiScene* scene = importer.ReadFile(filePath, aiProcess_Triangulate | aiProcess_GenSmoothNormals | aiProcess_FlipUVs | aiProcess_JoinIdenticalVertices);
    
    if (!scene || scene->mFlags & AI_SCENE_FLAGS_INCOMPLETE || !scene->mRootNode) {
        return false;
    }

    // 提取第一个网格（假设FBX仅包含目标网格）
    aiMesh* mesh = scene->mMeshes[0];
    vertices.reserve(mesh->mNumVertices);
    for (unsigned int i = 0; i < mesh->mNumVertices; ++i) {
        aiVector3D pos = mesh->mVertices[i];
        vertices.emplace_back(pos.x, pos.y, pos.z);
    }

    indices.reserve(mesh->mNumFaces * 3);
    for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
        aiFace face = mesh->mFaces[i];
        for (unsigned int j = 0; j < face.mNumIndices; ++j) {
            indices.push_back(face.mIndices[j]);
        }
    }
    return true;
}

• 注意：aiProcess_Triangulate确保网格被三角化（PhysX仅支持三角网格）；aiProcess_JoinIdenticalVertices合并重复顶点，减少数据冗余。

三、数据转换与PhysX烘焙 #

1. 凸网格烘焙 #

若原始FBX凸网格非严格凸，可启用自动凸包计算；若为严格凸，可关闭该标志提升性能：

physx::PxConvexMesh* bakeConvexMesh(physx::PxCooking* cooking, const std::vector<physx::PxVec3>& vertices) {
    physx::PxConvexMeshDesc convexDesc;
    convexDesc.points.count = vertices.size();
    convexDesc.points.stride = sizeof(physx::PxVec3);
    convexDesc.points.data = vertices.data();
    convexDesc.flags = physx::PxConvexFlag::eCOMPUTE_CONVEX; // 自动计算最小凸包

    physx::PxDefaultMemoryOutputStream buf;
    if (!cooking->cookConvexMesh(convexDesc, buf)) {
        return nullptr;
    }

    physx::PxDefaultMemoryInputData input(buf.getData(), buf.getSize());
    return cooking->createConvexMesh(input);
}

2. 凹网格烘焙 #

凹网格需烘焙为PxTriangleMesh，仅适用于静态碰撞体：

physx::PxTriangleMesh* bakeConcaveMesh(physx::PxCooking* cooking, const std::vector<physx::PxVec3>& vertices, const std::vector<physx::PxU32>& indices) {
    physx::PxTriangleMeshDesc triDesc;
    triDesc.points.count = vertices.size();
    triDesc.points.stride = sizeof(physx::PxVec3);
    triDesc.points.data = vertices.data();

    triDesc.triangles.count = indices.size() / 3;
    triDesc.triangles.stride = 3 * sizeof(physx::PxU32);
    triDesc.triangles.data = indices.data();

    physx::PxDefaultMemoryOutputStream buf;
    if (!cooking->cookTriangleMesh(triDesc, buf)) {
        return nullptr;
    }

    physx::PxDefaultMemoryInputData input(buf.getData(), buf.getSize());
    return cooking->createTriangleMesh(input);
}

四、主流程调用 #

int main() {
    // 初始化PhysX（同环境准备部分）
    physx::PxFoundation* foundation = PxCreateFoundation(PX_PHYSICS_VERSION, gDefaultAllocatorCallback, gDefaultErrorCallback);
    physx::PxPhysics* physics = PxCreatePhysics(PX_PHYSICS_VERSION, *foundation, physx::PxTolerancesScale(), true);
    physx::PxCooking* cooking = PxCreateCooking(PX_PHYSICS_VERSION, *foundation, physx::PxCookingParams(physx::PxTolerancesScale()));

    // 加载凸、凹FBX网格
    std::vector<physx::PxVec3> convexVertices, concaveVertices;
    std::vector<physx::PxU32> concaveIndices;
    loadFBXMesh("convex_mesh.fbx", convexVertices, {}); // 凸网格烘焙无需索引
    loadFBXMesh("concave_mesh.fbx", concaveVertices, concaveIndices);

    // 执行烘焙
    physx::PxConvexMesh* convexMesh = bakeConvexMesh(cooking, convexVertices);
    physx::PxTriangleMesh* concaveMesh = bakeConcaveMesh(cooking, concaveVertices, concaveIndices);

    // 示例：用烘焙后的网格创建碰撞体
    if (convexMesh) {
        physx::PxRigidDynamic* convexActor = physics->createRigidDynamic(physx::PxTransform(physx::PxVec3(0, 5, 0)));
        physx::PxShape* convexShape = physics->createShape(physx::PxConvexMeshGeometry(convexMesh), *physics->createMaterial(0.5f, 0.5f, 0.2f));
        convexActor->attachShape(*convexShape);
        convexShape->release();
    }

    if (concaveMesh) {
        physx::PxRigidStatic* concaveActor = physics->createRigidStatic(physx::PxTransform(physx::PxVec3(0, 0, 0)));
        physx::PxShape* concaveShape = physics->createShape(physx::PxTriangleMeshGeometry(concaveMesh), *physics->createMaterial(0.5f, 0.5f, 0.2f));
        concaveActor->attachShape(*concaveShape);
        concaveShape->release();
    }

    // 资源清理
    if (convexMesh) convexMesh->release();
    if (concaveMesh) concaveMesh->release();
    cooking->release();
    physics->release();
    foundation->release();

    return 0;
}

关键注意事项 #

• 凸网格烘焙时，若原始网格是严格凸结构，可移除eCOMPUTE_CONVEX标志，跳过凸包计算以提升效率。
• 凹网格仅支持静态碰撞体（PxRigidStatic），动态物体不能直接使用凹网格碰撞体，需拆分为多个凸网格或使用凸分解工具处理。
• 若FBX包含多个子网格，需遍历scene->mMeshes数组逐个提取数据。
• 需提前实现PhysX默认的内存分配器与错误回调函数（示例中使用gDefaultAllocatorCallback和gDefaultErrorCallback）。

内容的提问来源于stack exchange，提问作者Kitiara