Drawing

The following script draws three objects for a vessel in orbit around Kerbin. A dashed green path shows a circular target orbit 250 km up. A flag marks the north pole in the map view, and a yellow arrow points prograde from the vessel. The script updates the label on the arrow with the vessel’s orbital speed.

CC#C++JavaLuaPython

#include <stdio.h>
#include <string.h>
#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#define sleep(seconds) Sleep((seconds) * 1000)
#else
#include <unistd.h>
#endif
#include <krpc_cnano.h>
#include <krpc_cnano/services/space_center.h>
#include <krpc_cnano/services/std_lib.h>
#include <krpc_cnano/services/ui.h>
#include <krpc_cnano/services/drawing.h>

int main() {
  krpc_connection_t conn;
  krpc_open(&conn, "COM0");
  krpc_connect(conn, "Drawing Example");

  krpc_SpaceCenter_Vessel_t vessel;
  krpc_SpaceCenter_ActiveVessel(conn, &vessel);
  krpc_dictionary_string_object_t bodies = KRPC_NULL_DICTIONARY;
  krpc_SpaceCenter_Bodies(conn, &bodies);
  krpc_SpaceCenter_CelestialBody_t kerbin;
  for (size_t i = 0; i < bodies.size; i++)
    if (!strcmp(bodies.entries[i].key, "Kerbin"))
      kerbin = bodies.entries[i].value;
  krpc_SpaceCenter_ReferenceFrame_t kerbin_ref;
  krpc_SpaceCenter_CelestialBody_ReferenceFrame(conn, &kerbin_ref, kerbin);

  // Draw a circular orbit 250 km above Kerbin, as a dashed green path with
  // a label
  double radius;
  krpc_SpaceCenter_CelestialBody_EquatorialRadius(conn, &radius, kerbin);
  double ut;
  krpc_SpaceCenter_UT(conn, &ut);
  krpc_SpaceCenter_Orbit_t orbit;
  krpc_SpaceCenter_Orbit_CreateFromOrbitalElements(
    conn, &orbit, kerbin, radius + 250000, 0, 0, 0, 0, 0, ut);
  krpc_Drawing_OrbitPath_t path;
  krpc_Drawing_AddOrbit(conn, &path, orbit, true);
  krpc_StdLib_ColorRGB_t green = {0, 1, 0};
  krpc_Drawing_OrbitPath_set_Color(conn, path, &green);
  krpc_Drawing_OrbitPath_set_Dashed(conn, path, true);
  krpc_Drawing_OrbitPath_set_Label(conn, path, "Target orbit");

  // Mark the north pole in the map view, with the game's flag icon
  krpc_tuple_double_double_double_t site;
  krpc_SpaceCenter_CelestialBody_SurfacePosition(
    conn, &site, kerbin, 90, 0, kerbin_ref);
  krpc_Drawing_AddMapMarker(
    conn, NULL, &site, kerbin_ref, KRPC_DRAWING_MAPMARKERICON_FLAG,
    "North pole", true);

  // Draw a yellow arrow from the vessel, pointing prograde
  krpc_SpaceCenter_ReferenceFrame_t orbital_ref;
  krpc_SpaceCenter_Vessel_OrbitalReferenceFrame(conn, &orbital_ref, vessel);
  krpc_tuple_double_double_double_t prograde = {0, 1, 0};
  krpc_Drawing_Line_t arrow;
  krpc_Drawing_AddDirectionFromCom(conn, &arrow, &prograde, orbital_ref, 10, true);
  krpc_StdLib_ColorRGB_t yellow = {1, 1, 0};
  krpc_Drawing_Line_set_Color(conn, arrow, &yellow);
  krpc_Drawing_Line_set_EndArrow(conn, arrow, true);

  // Label the arrow with the orbital speed of the vessel
  krpc_SpaceCenter_Orbit_t vessel_orbit;
  krpc_SpaceCenter_Vessel_Orbit(conn, &vessel_orbit, vessel);
  while (true) {
    double speed;
    krpc_SpaceCenter_Orbit_Speed(conn, &speed, vessel_orbit);
    char label[32];
    snprintf(label, sizeof(label), "%d m/s", (int)speed);
    krpc_Drawing_Line_set_Label(conn, arrow, label);
    sleep(1);
  }
}

The arrow is drawn in the flight scene. Switch to the map view to see the target orbit and the flag. Drawn objects remain until the script disconnects, which is why the script ends in a loop.

See also

Drawing for the other objects you can draw, including circles, arcs, boxes, spheres, points and navball markers.