AP_Radar: Corrections and fixes

- Fix arrow directions if using BTFL fonts
- Fix Radar panel item group IDx conflict with prior parameter (which caused FC lockup on boot)
- Fix peers array indexing, avoiding 0x800 internal error if all 6 peers are visible
- Fix peer persistence on OSD after signal loss

libraries/AP_OSD/AP_OSD_Screen.cpp

@@ -1039,6 +1039,7 @@ const AP_Param::GroupInfo AP_OSD_Screen::var_info[] = {
 	// @Range: 0 15
 	AP_SUBGROUPINFO(rrpm, "RPM", 62, AP_OSD_Screen, AP_OSD_Setting),
 #endif
+
     // @Param: RADAR_EN
     // @DisplayName: RADAR_EN
     // @Description: Displays iNav Radar info for peer aircraft
@@ -1711,12 +1712,11 @@ void AP_OSD_Screen::draw_radar(uint8_t x, uint8_t y)
             vertical_distance = 0.0f;
         }
         int32_t angle = wrap_360_cd(loc.get_bearing_to(peer_loc) - ahrs.yaw_sensor);
-        int32_t interval = 36000 / SYMBOL(SYM_ARROW_COUNT);
         if (distance < 2.0f) {
             //avoid fast rotating arrow at small distances
             angle = 0;
         }
-        char arrow = SYMBOL(SYM_ARROW_START) + ((angle + interval / 2) / interval) % SYMBOL(SYM_ARROW_COUNT);
+        char arrow = get_arrow_font_index(angle);
         backend->write(x, y, false, "%c%c", id + 65, arrow);
         draw_distance(x+2, y, distance);
         draw_vdistance(x+1, y+1, vertical_distance);

libraries/AP_Radar/AP_Radar.cpp

@@ -64,7 +64,7 @@ void AP_Radar::update(void)
     }
 
     // only healthy if the data is less than 3s old
-    _flags.healthy = (AP_HAL::millis() - _last_update_ms < RADAR_PEER_FRESH_TIME_MS);
+    _flags.healthy = ((AP_HAL::millis() - _last_update_ms) < RADAR_PEER_FRESH_TIME_MS);
 }
 
 void AP_Radar::handle_msg(const mavlink_message_t &msg)
@@ -107,16 +107,18 @@ radar_peer_t AP_Radar::get_peer(uint8_t id)
 bool AP_Radar::get_peer_healthy(uint8_t id)
 {
     return _state.peers[id].last_update > (AP_HAL::millis() - 3000) &&
-        !_state.peers[id].location.is_zero();
+        !_state.peers[id].location.is_zero() && _state.peers[id].lq > 0;
 }
 
 uint8_t AP_Radar::get_next_healthy_peer(uint8_t current_id)
 {
         // Try all available slots
 	for (uint8_t i = 1; i < RADAR_MAX_PEERS; i++) {
-            uint8_t next_peer = (current_id + i) % RADAR_MAX_PEERS;
-            if (get_peer_healthy(next_peer)) {
-                return next_peer;
+        uint8_t next_id = current_id + i;
+        uint8_t next_peer = next_id >= RADAR_MAX_PEERS ? next_id - RADAR_MAX_PEERS : next_id;
+        if (get_peer_healthy(next_peer))
+        {
+            return next_peer;
             }
         }
         return current_id;

libraries/AP_Radar/AP_Radar_MSP.cpp

@@ -56,7 +56,7 @@ void AP_Radar_MSP::update(void)
 void AP_Radar_MSP::handle_msp(const MSP::msp_radar_pos_message_t &pkt)
 {
     // record peer state
-    uint8_t id = pkt.radar_no;
+    uint8_t id = pkt.radar_no - 1U;
     peers[id].radar_no = pkt.radar_no;
     peers[id].state = pkt.state;
     peers[id].location = Location(pkt.lat, pkt.lon, pkt.alt, Location::AltFrame::ABSOLUTE);