Method ComputeSphereMapping

code/PostProcessing/ComputeUVMappingProcess.cpp:152–211

------------------------------------------------------------------------------------------------

// ------------------------------------------------------------------------------------------------
void ComputeUVMappingProcess::ComputeSphereMapping(aiMesh *mesh, const aiVector3D &axis, aiVector3D *out) {
    aiVector3D center, min, max;
    FindMeshCenter(mesh, center, min, max);

    // If the axis is one of x,y,z run a faster code path. It's worth the extra effort ...
    // currently the mapping axis will always be one of x,y,z, except if the
    // PretransformVertices step is used (it transforms the meshes into worldspace,
    // thus changing the mapping axis)
    if (axis * base_axis_x >= angle_epsilon) {

        // For each point get a normalized projection vector in the sphere,
        // get its longitude and latitude and map them to their respective
        // UV axes. Problems occur around the poles ... unsolvable.
        //
        // The spherical coordinate system looks like this:
        // x = cos(lon)*cos(lat)
        // y = sin(lon)*cos(lat)
        // z = sin(lat)
        //
        // Thus we can derive:
        // lat  = arcsin (z)
        // lon  = arctan (y/x)
        for (unsigned int pnt = 0; pnt < mesh->mNumVertices; ++pnt) {
            const aiVector3D diff = (mesh->mVertices[pnt] - center).Normalize();
            out[pnt] = aiVector3D((std::atan2(diff.z, diff.y) + AI_MATH_PI_F) / AI_MATH_TWO_PI_F,
                    (std::asin(diff.x) + AI_MATH_HALF_PI_F) / AI_MATH_PI_F, 0.0);
        }
    } else if (axis * base_axis_y >= angle_epsilon) {
        // ... just the same again
        for (unsigned int pnt = 0; pnt < mesh->mNumVertices; ++pnt) {
            const aiVector3D diff = (mesh->mVertices[pnt] - center).Normalize();
            out[pnt] = aiVector3D((std::atan2(diff.x, diff.z) + AI_MATH_PI_F) / AI_MATH_TWO_PI_F,
                    (std::asin(diff.y) + AI_MATH_HALF_PI_F) / AI_MATH_PI_F, 0.0);
        }
    } else if (axis * base_axis_z >= angle_epsilon) {
        // ... just the same again
        for (unsigned int pnt = 0; pnt < mesh->mNumVertices; ++pnt) {
            const aiVector3D diff = (mesh->mVertices[pnt] - center).Normalize();
            out[pnt] = aiVector3D((std::atan2(diff.y, diff.x) + AI_MATH_PI_F) / AI_MATH_TWO_PI_F,
                    (std::asin(diff.z) + AI_MATH_HALF_PI_F) / AI_MATH_PI_F, 0.0);
        }
    }
    // slower code path in case the mapping axis is not one of the coordinate system axes
    else {
        aiMatrix4x4 mTrafo;
        aiMatrix4x4::FromToMatrix(axis, base_axis_y, mTrafo);

        // again the same, except we're applying a transformation now
        for (unsigned int pnt = 0; pnt < mesh->mNumVertices; ++pnt) {
            const aiVector3D diff = ((mTrafo * mesh->mVertices[pnt]) - center).Normalize();
            out[pnt] = aiVector3D((std::atan2(diff.y, diff.x) + AI_MATH_PI_F) / AI_MATH_TWO_PI_F,
                    (std::asin(diff.z) + AI_MATH_HALF_PI_F) / AI_MATH_PI_F, 0.0);
        }
    }

    // Now find and remove UV seams. A seam occurs if a face has a tcoord
    // close to zero on the one side, and a tcoord close to one on the
    // other side.