SkeletonMeshBuilder.cpp

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/** @file  SkeletonMeshBuilder.cpp
 *  @brief Implementation of a little class to construct a dummy mesh for a skeleton
 */

#include <assimp/SkeletonMeshBuilder.h>
#include <assimp/scene.h>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// The constructor processes the given scene and adds a mesh there.
SkeletonMeshBuilder::SkeletonMeshBuilder(aiScene *pScene, aiNode *root, bool bKnobsOnly) {
    // nothing to do if there's mesh data already present at the scene
    if (pScene->mNumMeshes > 0 || pScene->mRootNode == nullptr) {
        return;
    }

    if (!root) {
        root = pScene->mRootNode;
    }

    mKnobsOnly = bKnobsOnly;

    // build some faces around each node
    CreateGeometry(root);

    // create a mesh to hold all the generated faces
    pScene->mNumMeshes = 1;
    pScene->mMeshes = new aiMesh *[1];
    pScene->mMeshes[0] = CreateMesh();
    // and install it at the root node
    root->mNumMeshes = 1;
    root->mMeshes = new unsigned int[1];
    root->mMeshes[0] = 0;

    // create a dummy material for the mesh
    if (pScene->mNumMaterials == 0) {
        pScene->mNumMaterials = 1;
        pScene->mMaterials = new aiMaterial *[1];
        pScene->mMaterials[0] = CreateMaterial();
    }
}

// ------------------------------------------------------------------------------------------------
// Recursively builds a simple mesh representation for the given node
void SkeletonMeshBuilder::CreateGeometry(const aiNode *pNode) {
    // add a joint entry for the node.
    const unsigned int vertexStartIndex = static_cast<unsigned int>(mVertices.size());

    // now build the geometry.
    if (pNode->mNumChildren > 0 && !mKnobsOnly) {
        // If the node has children, we build little pointers to each of them
        for (unsigned int a = 0; a < pNode->mNumChildren; a++) {
            // find a suitable coordinate system
            const aiMatrix4x4 &childTransform = pNode->mChildren[a]->mTransformation;
            aiVector3D childpos(childTransform.a4, childTransform.b4, childTransform.c4);
            ai_real distanceToChild = childpos.Length();
            if (distanceToChild < 0.0001)
                continue;
            aiVector3D up = aiVector3D(childpos).Normalize();

            aiVector3D orth(1.0, 0.0, 0.0);
            if (std::fabs(orth * up) > 0.99)
                orth.Set(0.0, 1.0, 0.0);

            aiVector3D front = (up ^ orth).Normalize();
            aiVector3D side = (front ^ up).Normalize();

            unsigned int localVertexStart = static_cast<unsigned int>(mVertices.size());
            mVertices.push_back(-front * distanceToChild * (ai_real)0.1);
            mVertices.push_back(childpos);
            mVertices.push_back(-side * distanceToChild * (ai_real)0.1);
            mVertices.push_back(-side * distanceToChild * (ai_real)0.1);
            mVertices.push_back(childpos);
            mVertices.push_back(front * distanceToChild * (ai_real)0.1);
            mVertices.push_back(front * distanceToChild * (ai_real)0.1);
            mVertices.push_back(childpos);
            mVertices.push_back(side * distanceToChild * (ai_real)0.1);
            mVertices.push_back(side * distanceToChild * (ai_real)0.1);
            mVertices.push_back(childpos);
            mVertices.push_back(-front * distanceToChild * (ai_real)0.1);

            mFaces.push_back(Face(localVertexStart + 0, localVertexStart + 1, localVertexStart + 2));
            mFaces.push_back(Face(localVertexStart + 3, localVertexStart + 4, localVertexStart + 5));
            mFaces.push_back(Face(localVertexStart + 6, localVertexStart + 7, localVertexStart + 8));
            mFaces.push_back(Face(localVertexStart + 9, localVertexStart + 10, localVertexStart + 11));
        }
    } else {
        // if the node has no children, it's an end node. Put a little knob there instead
        aiVector3D ownpos(pNode->mTransformation.a4, pNode->mTransformation.b4, pNode->mTransformation.c4);
        ai_real sizeEstimate = ownpos.Length() * ai_real(0.18);

        mVertices.push_back(aiVector3D(-sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(0.0, sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, -sizeEstimate));
        mVertices.push_back(aiVector3D(0.0, sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, -sizeEstimate));
        mVertices.push_back(aiVector3D(sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(0.0, -sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, -sizeEstimate));
        mVertices.push_back(aiVector3D(0.0, -sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(-sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, -sizeEstimate));

        mVertices.push_back(aiVector3D(-sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, sizeEstimate));
        mVertices.push_back(aiVector3D(0.0, sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(0.0, sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, sizeEstimate));
        mVertices.push_back(aiVector3D(sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(sizeEstimate, 0.0, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, sizeEstimate));
        mVertices.push_back(aiVector3D(0.0, -sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(0.0, -sizeEstimate, 0.0));
        mVertices.push_back(aiVector3D(0.0, 0.0, sizeEstimate));
        mVertices.push_back(aiVector3D(-sizeEstimate, 0.0, 0.0));

        mFaces.push_back(Face(vertexStartIndex + 0, vertexStartIndex + 1, vertexStartIndex + 2));
        mFaces.push_back(Face(vertexStartIndex + 3, vertexStartIndex + 4, vertexStartIndex + 5));
        mFaces.push_back(Face(vertexStartIndex + 6, vertexStartIndex + 7, vertexStartIndex + 8));
        mFaces.push_back(Face(vertexStartIndex + 9, vertexStartIndex + 10, vertexStartIndex + 11));
        mFaces.push_back(Face(vertexStartIndex + 12, vertexStartIndex + 13, vertexStartIndex + 14));
        mFaces.push_back(Face(vertexStartIndex + 15, vertexStartIndex + 16, vertexStartIndex + 17));
        mFaces.push_back(Face(vertexStartIndex + 18, vertexStartIndex + 19, vertexStartIndex + 20));
        mFaces.push_back(Face(vertexStartIndex + 21, vertexStartIndex + 22, vertexStartIndex + 23));
    }

    unsigned int numVertices = static_cast<unsigned int>(mVertices.size() - vertexStartIndex);
    if (numVertices > 0) {
        // create a bone affecting all the newly created vertices
        aiBone *bone = new aiBone;
        mBones.push_back(bone);
        bone->mName = pNode->mName;

        // calculate the bone offset matrix by concatenating the inverse transformations of all parents
        bone->mOffsetMatrix = aiMatrix4x4(pNode->mTransformation).Inverse();
        for (aiNode *parent = pNode->mParent; parent != nullptr; parent = parent->mParent)
            bone->mOffsetMatrix = aiMatrix4x4(parent->mTransformation).Inverse() * bone->mOffsetMatrix;

        // add all the vertices to the bone's influences
        bone->mNumWeights = numVertices;
        bone->mWeights = new aiVertexWeight[numVertices];
        for (unsigned int a = 0; a < numVertices; a++)
            bone->mWeights[a] = aiVertexWeight(vertexStartIndex + a, 1.0);

        // HACK: (thom) transform all vertices to the bone's local space. Should be done before adding
        // them to the array, but I'm tired now and I'm annoyed.
        aiMatrix4x4 boneToMeshTransform = aiMatrix4x4(bone->mOffsetMatrix).Inverse();
        for (unsigned int a = vertexStartIndex; a < mVertices.size(); a++)
            mVertices[a] = boneToMeshTransform * mVertices[a];
    }

    // and finally recurse into the children list
    for (unsigned int a = 0; a < pNode->mNumChildren; a++)
        CreateGeometry(pNode->mChildren[a]);
}

// ------------------------------------------------------------------------------------------------
// Creates the mesh from the internally accumulated stuff and returns it.
aiMesh *SkeletonMeshBuilder::CreateMesh() {
    aiMesh *mesh = new aiMesh();

    // add points
    mesh->mNumVertices = static_cast<unsigned int>(mVertices.size());
    mesh->mVertices = new aiVector3D[mesh->mNumVertices];
    std::copy(mVertices.begin(), mVertices.end(), mesh->mVertices);

    mesh->mNormals = new aiVector3D[mesh->mNumVertices];

    // add faces
    mesh->mNumFaces = static_cast<unsigned int>(mFaces.size());
    mesh->mFaces = new aiFace[mesh->mNumFaces];
    for (unsigned int a = 0; a < mesh->mNumFaces; a++) {
        const Face &inface = mFaces[a];
        aiFace &outface = mesh->mFaces[a];
        outface.mNumIndices = 3;
        outface.mIndices = new unsigned int[3];
        outface.mIndices[0] = inface.mIndices[0];
        outface.mIndices[1] = inface.mIndices[1];
        outface.mIndices[2] = inface.mIndices[2];

        // Compute per-face normals ... we don't want the bones to be smoothed ... they're built to visualize
        // the skeleton, so it's good if there's a visual difference to the rest of the geometry
        aiVector3D nor = ((mVertices[inface.mIndices[2]] - mVertices[inface.mIndices[0]]) ^
                          (mVertices[inface.mIndices[1]] - mVertices[inface.mIndices[0]]));

        if (nor.Length() < 1e-5) /* ensure that FindInvalidData won't remove us ...*/
            nor = aiVector3D(1.0, 0.0, 0.0);

        for (unsigned int n = 0; n < 3; ++n)
            mesh->mNormals[inface.mIndices[n]] = nor;
    }

    // add the bones
    mesh->mNumBones = static_cast<unsigned int>(mBones.size());
    mesh->mBones = new aiBone *[mesh->mNumBones];
    std::copy(mBones.begin(), mBones.end(), mesh->mBones);

    // default
    mesh->mMaterialIndex = 0;

    return mesh;
}

// ------------------------------------------------------------------------------------------------
// Creates a dummy material and returns it.
aiMaterial *SkeletonMeshBuilder::CreateMaterial() {
    aiMaterial *matHelper = new aiMaterial;

    // Name
    aiString matName(std::string("SkeletonMaterial"));
    matHelper->AddProperty(&matName, AI_MATKEY_NAME);

    // Prevent backface culling
    const int no_cull = 1;
    matHelper->AddProperty(&no_cull, 1, AI_MATKEY_TWOSIDED);

    return matHelper;
}