/src/assimp/code/PostProcessing/ConvertToLHProcess.cpp

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/** @file  MakeLeftHandedProcess.cpp
 *  @brief Implementation of the post processing step to convert all
 *  imported data to a left-handed coordinate system.
 *
 *  Face order & UV flip are also implemented here, for the sake of a
 *  better location.
 */

#include "ConvertToLHProcess.h"
#include <assimp/postprocess.h>
#include <assimp/scene.h>
#include <assimp/DefaultLogger.hpp>

using namespace Assimp;

#ifndef ASSIMP_BUILD_NO_MAKELEFTHANDED_PROCESS

namespace {

template <typename aiMeshType>
void flipUVs(aiMeshType *pMesh) {
    if (pMesh == nullptr) {
        return;
    }
    // mirror texture y coordinate
    for (unsigned int tcIdx = 0; tcIdx < AI_MAX_NUMBER_OF_TEXTURECOORDS; tcIdx++) {
        if (!pMesh->HasTextureCoords(tcIdx)) {
            break;
        }

        for (unsigned int vIdx = 0; vIdx < pMesh->mNumVertices; vIdx++) {
            pMesh->mTextureCoords[tcIdx][vIdx].y = 1.0f - pMesh->mTextureCoords[tcIdx][vIdx].y;
        }
    }
}

} // namespace

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool MakeLeftHandedProcess::IsActive(unsigned int pFlags) const {
    return 0 != (pFlags & aiProcess_MakeLeftHanded);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void MakeLeftHandedProcess::Execute(aiScene *pScene) {
    // Check for an existent root node to proceed
    ai_assert(pScene->mRootNode != nullptr);
    ASSIMP_LOG_DEBUG("MakeLeftHandedProcess begin");

    // recursively convert all the nodes
    ProcessNode(pScene->mRootNode, aiMatrix4x4());

    // process the meshes accordingly
    for (unsigned int a = 0; a < pScene->mNumMeshes; ++a) {
        ProcessMesh(pScene->mMeshes[a]);
    }

    // process the materials accordingly
    for (unsigned int a = 0; a < pScene->mNumMaterials; ++a) {
        ProcessMaterial(pScene->mMaterials[a]);
    }

    // transform all animation channels as well
    for (unsigned int a = 0; a < pScene->mNumAnimations; a++) {
        aiAnimation *anim = pScene->mAnimations[a];
        for (unsigned int b = 0; b < anim->mNumChannels; b++) {
            aiNodeAnim *nodeAnim = anim->mChannels[b];
            ProcessAnimation(nodeAnim);
        }
    }

    // process the cameras accordingly
    for( unsigned int a = 0; a < pScene->mNumCameras; ++a)
    {
        ProcessCamera(pScene->mCameras[a]);
    }
    ASSIMP_LOG_DEBUG("MakeLeftHandedProcess finished");
}

// ------------------------------------------------------------------------------------------------
// Recursively converts a node, all of its children and all of its meshes
void MakeLeftHandedProcess::ProcessNode(aiNode *pNode, const aiMatrix4x4 &pParentGlobalRotation) {
    // mirror all base vectors at the local Z axis
    pNode->mTransformation.c1 = -pNode->mTransformation.c1;
    pNode->mTransformation.c2 = -pNode->mTransformation.c2;
    pNode->mTransformation.c3 = -pNode->mTransformation.c3;
    pNode->mTransformation.c4 = -pNode->mTransformation.c4;

    // now invert the Z axis again to keep the matrix determinant positive.
    // The local meshes will be inverted accordingly so that the result should look just fine again.
    pNode->mTransformation.a3 = -pNode->mTransformation.a3;
    pNode->mTransformation.b3 = -pNode->mTransformation.b3;
    pNode->mTransformation.c3 = -pNode->mTransformation.c3;
    pNode->mTransformation.d3 = -pNode->mTransformation.d3; // useless, but anyways...

    // continue for all children
    for (size_t a = 0; a < pNode->mNumChildren; ++a) {
        ProcessNode(pNode->mChildren[a], pParentGlobalRotation * pNode->mTransformation);
    }
}

// ------------------------------------------------------------------------------------------------
// Converts a single mesh to left handed coordinates.
void MakeLeftHandedProcess::ProcessMesh(aiMesh *pMesh) {
    if (nullptr == pMesh) {
        ASSIMP_LOG_ERROR("Nullptr to mesh found.");
        return;
    }
    // mirror positions, normals and stuff along the Z axis
    for (size_t a = 0; a < pMesh->mNumVertices; ++a) {
        pMesh->mVertices[a].z *= -1.0f;
        if (pMesh->HasNormals()) {
            pMesh->mNormals[a].z *= -1.0f;
        }
        if (pMesh->HasTangentsAndBitangents()) {
            pMesh->mTangents[a].z *= -1.0f;
            pMesh->mBitangents[a].z *= -1.0f;
        }
    }

    // mirror anim meshes positions, normals and stuff along the Z axis
    for (size_t m = 0; m < pMesh->mNumAnimMeshes; ++m) {
        for (size_t a = 0; a < pMesh->mAnimMeshes[m]->mNumVertices; ++a) {
            pMesh->mAnimMeshes[m]->mVertices[a].z *= -1.0f;
            if (pMesh->mAnimMeshes[m]->HasNormals()) {
                pMesh->mAnimMeshes[m]->mNormals[a].z *= -1.0f;
            }
            if (pMesh->mAnimMeshes[m]->HasTangentsAndBitangents()) {
                pMesh->mAnimMeshes[m]->mTangents[a].z *= -1.0f;
                pMesh->mAnimMeshes[m]->mBitangents[a].z *= -1.0f;
            }
        }
    }

    // mirror offset matrices of all bones
    for (size_t a = 0; a < pMesh->mNumBones; ++a) {
        aiBone *bone = pMesh->mBones[a];
        bone->mOffsetMatrix.a3 = -bone->mOffsetMatrix.a3;
        bone->mOffsetMatrix.b3 = -bone->mOffsetMatrix.b3;
        bone->mOffsetMatrix.d3 = -bone->mOffsetMatrix.d3;
        bone->mOffsetMatrix.c1 = -bone->mOffsetMatrix.c1;
        bone->mOffsetMatrix.c2 = -bone->mOffsetMatrix.c2;
        bone->mOffsetMatrix.c4 = -bone->mOffsetMatrix.c4;
    }

    // mirror bitangents as well as they're derived from the texture coords
    if (pMesh->HasTangentsAndBitangents()) {
        for (unsigned int a = 0; a < pMesh->mNumVertices; a++)
            pMesh->mBitangents[a] *= -1.0f;
    }
}

// ------------------------------------------------------------------------------------------------
// Converts a single material to left handed coordinates.
void MakeLeftHandedProcess::ProcessMaterial(aiMaterial *_mat) {
    if (nullptr == _mat) {
        ASSIMP_LOG_ERROR("Nullptr to aiMaterial found.");
        return;
    }

    aiMaterial *mat = (aiMaterial *)_mat;
    for (unsigned int a = 0; a < mat->mNumProperties; ++a) {
        aiMaterialProperty *prop = mat->mProperties[a];

        // Mapping axis for UV mappings?
        if (!::strcmp(prop->mKey.data, "$tex.mapaxis")) {
            ai_assert(prop->mDataLength >= sizeof(aiVector3D)); // something is wrong with the validation if we end up here
            aiVector3D *pff = (aiVector3D *)prop->mData;
            pff->z *= -1.f;
        }
    }
}

// ------------------------------------------------------------------------------------------------
// Converts the given animation to LH coordinates.
void MakeLeftHandedProcess::ProcessAnimation(aiNodeAnim *pAnim) {
    // position keys
    for (unsigned int a = 0; a < pAnim->mNumPositionKeys; a++)
        pAnim->mPositionKeys[a].mValue.z *= -1.0f;

    // rotation keys
    for (unsigned int a = 0; a < pAnim->mNumRotationKeys; a++) {
        pAnim->mRotationKeys[a].mValue.x *= -1.0f;
        pAnim->mRotationKeys[a].mValue.y *= -1.0f;
    }
}

// ------------------------------------------------------------------------------------------------
// Converts a single camera to left handed coordinates.
void MakeLeftHandedProcess::ProcessCamera( aiCamera* pCam)
{
    pCam->mLookAt = ai_real(2.0f) * pCam->mPosition - pCam->mLookAt;
}

#endif // !!  ASSIMP_BUILD_NO_MAKELEFTHANDED_PROCESS
#ifndef ASSIMP_BUILD_NO_FLIPUVS_PROCESS
// # FlipUVsProcess

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
FlipUVsProcess::FlipUVsProcess() = default;

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
FlipUVsProcess::~FlipUVsProcess() = default;

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool FlipUVsProcess::IsActive(unsigned int pFlags) const {
    return 0 != (pFlags & aiProcess_FlipUVs);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void FlipUVsProcess::Execute(aiScene *pScene) {
    ASSIMP_LOG_DEBUG("FlipUVsProcess begin");
    for (unsigned int i = 0; i < pScene->mNumMeshes; ++i)
        ProcessMesh(pScene->mMeshes[i]);

    for (unsigned int i = 0; i < pScene->mNumMaterials; ++i)
        ProcessMaterial(pScene->mMaterials[i]);
    ASSIMP_LOG_DEBUG("FlipUVsProcess finished");
}

// ------------------------------------------------------------------------------------------------
// Converts a single material
void FlipUVsProcess::ProcessMaterial(aiMaterial *_mat) {
    aiMaterial *mat = (aiMaterial *)_mat;
    for (unsigned int a = 0; a < mat->mNumProperties; ++a) {
        aiMaterialProperty *prop = mat->mProperties[a];
        if (!prop) {
            ASSIMP_LOG_VERBOSE_DEBUG("Property is null");
            continue;
        }

        // UV transformation key?
        if (!::strcmp(prop->mKey.data, "$tex.uvtrafo")) {
            ai_assert(prop->mDataLength >= sizeof(aiUVTransform)); // something is wrong with the validation if we end up here
            aiUVTransform *uv = (aiUVTransform *)prop->mData;

            // just flip it, that's everything
            uv->mTranslation.y *= -1.f;
            uv->mRotation *= -1.f;
        }
    }
}

// ------------------------------------------------------------------------------------------------
// Converts a single mesh
void FlipUVsProcess::ProcessMesh(aiMesh *pMesh) {
    flipUVs(pMesh);
    for (unsigned int idx = 0; idx < pMesh->mNumAnimMeshes; idx++) {
        flipUVs(pMesh->mAnimMeshes[idx]);
    }
}

#endif // !ASSIMP_BUILD_NO_FLIPUVS_PROCESS
#ifndef ASSIMP_BUILD_NO_FLIPWINDING_PROCESS
// # FlipWindingOrderProcess

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool FlipWindingOrderProcess::IsActive(unsigned int pFlags) const {
    return 0 != (pFlags & aiProcess_FlipWindingOrder);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void FlipWindingOrderProcess::Execute(aiScene *pScene) {
    ASSIMP_LOG_DEBUG("FlipWindingOrderProcess begin");
    for (unsigned int i = 0; i < pScene->mNumMeshes; ++i)
        ProcessMesh(pScene->mMeshes[i]);
    ASSIMP_LOG_DEBUG("FlipWindingOrderProcess finished");
}

// ------------------------------------------------------------------------------------------------
// Converts a single mesh
void FlipWindingOrderProcess::ProcessMesh(aiMesh *pMesh) {
    // invert the order of all faces in this mesh
    for (unsigned int a = 0; a < pMesh->mNumFaces; a++) {
        aiFace &face = pMesh->mFaces[a];
        for (unsigned int b = 0; b < face.mNumIndices / 2; b++) {
            std::swap(face.mIndices[b], face.mIndices[face.mNumIndices - 1 - b]);
        }
    }

    // invert the order of all components in this mesh anim meshes
    for (unsigned int m = 0; m < pMesh->mNumAnimMeshes; m++) {
        aiAnimMesh *animMesh = pMesh->mAnimMeshes[m];
        unsigned int numVertices = animMesh->mNumVertices;
        if (animMesh->HasPositions()) {
            for (unsigned int a = 0; a < numVertices; a++) {
                std::swap(animMesh->mVertices[a], animMesh->mVertices[numVertices - 1 - a]);
            }
        }
        if (animMesh->HasNormals()) {
            for (unsigned int a = 0; a < numVertices; a++) {
                std::swap(animMesh->mNormals[a], animMesh->mNormals[numVertices - 1 - a]);
            }
        }
        for (unsigned int i = 0; i < AI_MAX_NUMBER_OF_TEXTURECOORDS; i++) {
            if (animMesh->HasTextureCoords(i)) {
                for (unsigned int a = 0; a < numVertices; a++) {
                    std::swap(animMesh->mTextureCoords[i][a], animMesh->mTextureCoords[i][numVertices - 1 - a]);
                }
            }
        }
        if (animMesh->HasTangentsAndBitangents()) {
            for (unsigned int a = 0; a < numVertices; a++) {
                std::swap(animMesh->mTangents[a], animMesh->mTangents[numVertices - 1 - a]);
                std::swap(animMesh->mBitangents[a], animMesh->mBitangents[numVertices - 1 - a]);
            }
        }
        for (unsigned int v = 0; v < AI_MAX_NUMBER_OF_COLOR_SETS; v++) {
            if (animMesh->HasVertexColors(v)) {
                for (unsigned int a = 0; a < numVertices; a++) {
                    std::swap(animMesh->mColors[v][a], animMesh->mColors[v][numVertices - 1 - a]);
                }
            }
        }
    }
}

#endif // !! ASSIMP_BUILD_NO_FLIPWINDING_PROCESS

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Created: 2026-09-14 07:44