AP_OSD: allow scripting override and add getters

add semaphore protection for scripting bindings
Add get_semaphore() to AP_OSD_Backend that delegates to the parent
AP_OSD semaphore. Add semaphore keyword to scripting bindings so that
all OSD method calls from Lua are thread-safe with respect to the
OSD update thread.

Co-Authored-By: Iampete1 <iampete@hotmail.co.uk>

libraries/AP_OSD/AP_OSD.cpp

@@ -320,6 +320,11 @@ void AP_OSD::init()
 
 bool AP_OSD::init_backend(const AP_OSD::osd_types type, const uint8_t instance)
 {
+    // don't re-initialize if backend already exists
+    if (_backends[instance] != nullptr) {
+        return false;
+    }
+
     // check if we can run this backend instance in parallel with backend instance 0
     if (instance > 0) {
         if (_backends[0] && !_backends[0]->is_compatible_with_backend_type(type)) {
@@ -403,7 +408,20 @@ void AP_OSD::osd_thread()
             update_stats();
             update_current_screen();
         }
-        update_osd();
+#if AP_SCRIPTING_ENABLED
+        if (!scripting_override) {
+#endif
+            update_osd();
+#if AP_SCRIPTING_ENABLED
+        } else {
+            override_count++;
+            if (override_count > 20) {
+                // timeout after 2 seconds and return to normal OSD
+                scripting_override = false;
+                override_count = 0;
+            }
+        }
+#endif // AP_SCRIPTING_ENABLED
     }
 }
 

libraries/AP_OSD/AP_OSD.h

@@ -657,6 +657,20 @@ public:
     void enable() {
         _disable = false;
     }
+#if AP_SCRIPTING_ENABLED
+    AP_OSD_Backend *scripting_get_backend() {
+        scripting_override = true;
+        override_count = 0;
+        return _backends[0];
+    }
+    void draw_screen() {
+        if (scripting_override) {
+            update_osd();
+        }
+    }
+    bool display_disabled() const { return _disable; }
+    uint8_t get_screen() const { return current_screen; }
+#endif // AP_SCRIPTING_ENABLED
 
     AP_OSD_AbstractScreen& get_screen(uint8_t idx) {
 #if OSD_PARAM_ENABLED
@@ -718,6 +732,11 @@ private:
     AP_OSD_Backend *_backends[OSD_MAX_INSTANCES];
     uint8_t _backend_count;
 
+#if AP_SCRIPTING_ENABLED
+    // bool for scripting override and counter to timeout override
+    bool scripting_override;
+    uint8_t override_count;
+#endif // AP_SCRIPTING_ENABLED
     static AP_OSD *_singleton;
     // multi-thread access support
     HAL_Semaphore _sem;

libraries/AP_OSD/AP_OSD_Backend.h

@@ -61,6 +61,16 @@ public:
     // called by the OSD thread once
     virtual void osd_thread_run_once() { return; }
 
+#if OSD_ENABLED && AP_SCRIPTING_ENABLED
+    // passthrough OSD functions for use by scripting
+    bool display_disabled() const { return _osd.display_disabled(); }
+    uint8_t get_screen() const { return _osd.get_screen(); }
+    void draw_screen() { _osd.draw_screen(); }
+
+    // get semaphore for thread-safe access from scripting
+    HAL_Semaphore &get_semaphore() { return _osd.get_semaphore(); }
+#endif
+
     AP_OSD * get_osd()
     {
         return &_osd;