Open-Harbor/osrm-backend
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Add code comments and document some magic constants.

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This commit is contained in:
Daniel Patterson 2016-08-22 23:49:09 -07:00 committed by Moritz Kobitzsch
parent c8eb2b2d11
commit 3dd7732ffc
1 changed files with 23 additions and 11 deletions
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34
src/engine/plugins/tile.cpp
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@ -31,6 +31,9 @@ namespace plugins
{
namespace detail
{
// TODO: Port all this encoding logic to https://github.com/mapbox/vector-tile, which wasn't available
// when this code was originally written.
// Simple container class for WGS84 coordinates
template <typename T> struct Point final
{
@ -40,12 +43,6 @@ template <typename T> struct Point final
const T y;
};
// from mapnik-vector-tile
namespace pbf
{
inline unsigned encode_length(const unsigned len) { return (len << 3u) | 2u; }
}
struct BBox final
{
BBox(const double _minx, const double _miny, const double _maxx, const double _maxy)
@ -110,15 +107,20 @@ inline bool encodeLinestring(const FixedLine &line,
return false;
}
const unsigned line_to_length = static_cast<const unsigned>(line_size) - 1;
const unsigned LINETO_count = static_cast<const unsigned>(line_size) - 1;
auto pt = line.begin();
geometry.add_element(9); // move_to | (1 << 3)
const constexpr int MOVETO_COMMAND = 9;
geometry.add_element(MOVETO_COMMAND); // move_to | (1 << 3)
geometry.add_element(protozero::encode_zigzag32(pt->x - start_x));
geometry.add_element(protozero::encode_zigzag32(pt->y - start_y));
start_x = pt->x;
start_y = pt->y;
geometry.add_element(detail::pbf::encode_length(line_to_length));
// This means LINETO repeated N times
// See: https://github.com/mapbox/vector-tile-spec/tree/master/2.1#example-command-integers
geometry.add_element((LINETO_count << 3u) | 2u);
// Now that we've issued the LINETO REPEAT N command, we append
// N coordinate pairs immediately after the command.
for (++pt; pt != line.end(); ++pt)
{
const std::int32_t dx = pt->x - start_x;
@ -135,7 +137,8 @@ inline bool encodeLinestring(const FixedLine &line,
// Encodes a point
inline bool encodePoint(const FixedPoint &pt, protozero::packed_field_uint32 &geometry)
{
geometry.add_element(9);
const constexpr int MOVETO_COMMAND = 9;
geometry.add_element(MOVETO_COMMAND);
const std::int32_t dx = pt.x;
const std::int32_t dy = pt.y;
// Manual zigzag encoding.
@ -252,14 +255,23 @@ Status TilePlugin::HandleRequest(const api::TileParameters &parameters, std::str
// This hits the OSRM StaticRTree
const auto edges = facade.GetEdgesInBox(southwest, northeast);
// Vector tiles encode data values as lookup tables. This vector is the lookup table
// for integer values
std::vector<int> used_line_ints;
// While constructing the tile, we keep track of which integers we have in our table
// and their offsets, so multiple features can re-use the same values
std::unordered_map<int, std::size_t> line_int_offsets;
uint8_t max_datasource_id = 0;
// Same idea for street names - one lookup table for names for all features
std::vector<std::string> names;
// And an index of the names and their position in the list
std::unordered_map<std::string, std::size_t> name_offsets;
// And again for integer values used by points.
std::vector<int> used_point_ints;
std::unordered_map<int, std::size_t> point_int_offsets;
uint8_t max_datasource_id = 0;
std::vector<std::vector<detail::TurnData>> all_turn_data;
const auto use_line_value = [&used_line_ints, &line_int_offsets](const int &value) {