Feature/serve screenshots (#1003)

* Take screnshots using lua function, returning screenshot number. Add screenshot endpoint.
* Change capitalization from screenShot to screenshot
* Fix screenshot filename collision bug when using multiple windows.

include/openspace/engine/windowdelegate.h

@@ -107,7 +107,7 @@ struct WindowDelegate {
 
     bool (*isFisheyeRendering)() = []() { return false; };
 
-    void (*takeScreenshot)(bool applyWarping) = [](bool) { };
+    unsigned int(*takeScreenshot)(bool applyWarping) = [](bool) { return 0u; };
 
     void (*swapBuffer)() = []() {};
 

include/openspace/rendering/renderengine.h

@@ -142,9 +142,14 @@ public:
     void setResolveData(ghoul::Dictionary resolveData);
 
     /**
-     * Mark that one screenshot should be taken
+     * Take a screenshot and store in the ${SCREENSHOTS} directory
      */
-    void takeScreenShot();
+    void takeScreenshot();
+
+    /**
+     * Get the filename of the latest screenshot
+     */
+    unsigned int latestScreenshotNumber() const;
 
     /**
      * Returns the Lua library that contains all Lua functions available to affect the
@@ -187,8 +192,6 @@ private:
     properties::BoolProperty _showVersionInfo;
     properties::BoolProperty _showCameraInfo;
 
-    properties::TriggerProperty _takeScreenshot;
-    bool _shouldTakeScreenshot = false;
     properties::BoolProperty _applyWarping;
     properties::BoolProperty _showFrameInformation;
 #ifdef OPENSPACE_WITH_INSTRUMENTATION
@@ -226,6 +229,7 @@ private:
     properties::Vec3Property _masterRotation;
     
     uint64_t _frameNumber = 0;
+    unsigned int _latestScreenshotNumber = 0;
 
     std::vector<ghoul::opengl::ProgramObject*> _programs;