{

// We remove the blanks here from the material array. I.e. materials without a diffuse color

std::vector<boost::optional<std::array<float, 4> > > diffuse_color_array;

for (std::vector<IfcGeom::Material>::const_iterator it = geom->geometry().materials().begin(); it != geom->geometry().materials().end(); ++it) {

const IfcGeom::Material& mat = *it;

if (mat.hasDiffuse()) {

const double* color = mat.diffuse();

diffuse_color_array.push_back(std::array<float, 4>{

static_cast<float>(color[0]),

static_cast<float>(color[1]),

static_cast<float>(color[2]),

mat.hasTransparency() ? static_cast<float>(1. - mat.transparency()) : 1.f

});

} else {

diffuse_color_array.emplace_back();

}

std::map<int, int> orig_to_condensed_index_map;

std::vector<float> diffuse_color_array_condensed;

int new_index = 0;

for (int orig = 0; orig < diffuse_color_array.size(); ++orig) {

auto& m = diffuse_color_array[orig];

if (m) {

for (int i = 0; i < 4; ++i) {

diffuse_color_array_condensed.push_back((*m)[i]);

orig_to_condensed_index_map[orig] = new_index++;

}

}

swrite(s, std::string((char*) diffuse_color_array_condensed.data(), diffuse_color_array_condensed.size() * sizeof(float)));

std::vector<int32_t> material_indices;

for (std::vector<int>::const_iterator it = geom->geometry().material_ids().begin(); it != geom->geometry().material_ids().end(); ++it) {

// @todo use something like std::equal_range() ?

auto jt = orig_to_condensed_index_map.find(*it);

if (jt == orig_to_condensed_index_map.end()) {

material_indices.push_back(-1);

} else {

material_indices.push_back(jt->second);

}

}

swrite(s, std::string((char*) material_indices.data(), material_indices.size() * sizeof(int32_t)));