C++ GeometryCoordinates::front方法代码示例

static GeometryCoordinates fromClipperPath(const ClipperLib::Path& path) {
    GeometryCoordinates result;
    result.reserve(path.size() + 1);
    
    result.reserve(path.size());
    for (const auto& p : path) {
        using Coordinate = GeometryCoordinates::coordinate_type;
        assert(p.x >= std::numeric_limits<Coordinate>::min());
        assert(p.x <= std::numeric_limits<Coordinate>::max());
        assert(p.y >= std::numeric_limits<Coordinate>::min());
        assert(p.y <= std::numeric_limits<Coordinate>::max());
        result.emplace_back(Coordinate(p.x), Coordinate(p.y));
    }
    
    // Clipper does not repeat initial point, but our geometry model requires it.
    if (!result.empty()) {
        result.push_back(result.front());
    }
    
    return result;
}

void LineBucket::addGeometry(const GeometryCoordinates& vertices) {
    const GLsizei len = [&vertices] {
        GLsizei l = static_cast<GLsizei>(vertices.size());
        // If the line has duplicate vertices at the end, adjust length to remove them.
        while (l > 2 && vertices[l - 1] == vertices[l - 2]) {
            l--;
        }
        return l;
    }();

    if (len < 2) {
        // fprintf(stderr, "a line must have at least two vertices\n");
        return;
    }

    const float miterLimit = layout.join == JoinType::Bevel ? 1.05f : float(layout.miterLimit);

    const double sharpCornerOffset = SHARP_CORNER_OFFSET * (util::EXTENT / (util::tileSize * overscaling));

    const GeometryCoordinate firstVertex = vertices.front();
    const GeometryCoordinate lastVertex = vertices[len - 1];
    const bool closed = firstVertex == lastVertex;

    if (len == 2 && closed) {
        // fprintf(stderr, "a line may not have coincident points\n");
        return;
    }

    const CapType beginCap = layout.cap;
    const CapType endCap = closed ? CapType::Butt : CapType(layout.cap);

    int8_t flip = 1;
    double distance = 0;
    bool startOfLine = true;
    GeometryCoordinate currentVertex = GeometryCoordinate::null(), prevVertex = GeometryCoordinate::null(),
               nextVertex = GeometryCoordinate::null();
    vec2<double> prevNormal = vec2<double>::null(), nextNormal = vec2<double>::null();

    // the last three vertices added
    e1 = e2 = e3 = -1;

    if (closed) {
        currentVertex = vertices[len - 2];
        nextNormal = util::perp(util::unit(vec2<double>(firstVertex - currentVertex)));
    }

    const GLint startVertex = vertexBuffer.index();
    std::vector<TriangleElement> triangleStore;

    for (GLsizei i = 0; i < len; ++i) {
        if (closed && i == len - 1) {
            // if the line is closed, we treat the last vertex like the first
            nextVertex = vertices[1];
        } else if (i + 1 < len) {
            // just the next vertex
            nextVertex = vertices[i + 1];
        } else {
            // there is no next vertex
            nextVertex = GeometryCoordinate::null();
        }

        // if two consecutive vertices exist, skip the current one
        if (nextVertex && vertices[i] == nextVertex) {
            continue;
        }

        if (nextNormal) {
            prevNormal = nextNormal;
        }
        if (currentVertex) {
            prevVertex = currentVertex;
        }

        currentVertex = vertices[i];

        // Calculate the normal towards the next vertex in this line. In case
        // there is no next vertex, pretend that the line is continuing straight,
        // meaning that we are just using the previous normal.
        nextNormal = nextVertex ? util::perp(util::unit(vec2<double>(nextVertex - currentVertex)))
                                : prevNormal;

        // If we still don't have a previous normal, this is the beginning of a
        // non-closed line, so we're doing a straight "join".
        if (!prevNormal) {
            prevNormal = nextNormal;
        }

        // Determine the normal of the join extrusion. It is the angle bisector
        // of the segments between the previous line and the next line.
        vec2<double> joinNormal = util::unit(prevNormal + nextNormal);

        /*  joinNormal     prevNormal
         *             ↖      ↑
         *                .________. prevVertex
         *                |
         * nextNormal  ←  |  currentVertex
         *                |
         *     nextVertex !
         *
         */
//.........这里部分代码省略.........