Write screenshots to file asynchronously

CHANGELOG.md

@@ -17,6 +17,7 @@
     Bug #6129: Player avatar not displayed correctly for large window sizes when GUI scaling active
     Bug #6131: Item selection in the avatar window not working correctly for large window sizes
     Bug #6133: Cannot reliably sneak or steal in the sight of the NPCs siding with player
+    Bug #6143: Capturing a screenshot makes engine to be a temporary unresponsive
     Feature #2780: A way to see current OpenMW version in the console
     Feature #5489: MCP: Telekinesis fix for activators
     Feature #6017: Separate persistent and temporary cell references when saving

apps/openmw/engine.cpp

@@ -670,6 +670,18 @@ void OMW::Engine::prepareEngine (Settings::Manager & settings)
         throw std::runtime_error("Invalid setting: 'preload num threads' must be >0");
     mWorkQueue = new SceneUtil::WorkQueue(numThreads);
 
+    mScreenCaptureOperation = new SceneUtil::AsyncScreenCaptureOperation(
+        mWorkQueue,
+        new SceneUtil::WriteScreenshotToFileOperation(
+            mCfgMgr.getScreenshotPath().string(),
+            Settings::Manager::getString("screenshot format", "General")
+        )
+    );
+
+    mScreenCaptureHandler = new osgViewer::ScreenCaptureHandler(mScreenCaptureOperation);
+
+    mViewer->addEventHandler(mScreenCaptureHandler);
+
     // Create input and UI first to set up a bootstrapping environment for
     // showing a loading screen and keeping the window responsive while doing so
 
@@ -814,14 +826,6 @@ void OMW::Engine::go()
     mViewer->setUseConfigureAffinity(false);
 #endif
 
-    mScreenCaptureOperation = new SceneUtil::WriteScreenshotToFileOperation(
-        mCfgMgr.getScreenshotPath().string(),
-        Settings::Manager::getString("screenshot format", "General"));
-
-    mScreenCaptureHandler = new osgViewer::ScreenCaptureHandler(mScreenCaptureOperation);
-
-    mViewer->addEventHandler(mScreenCaptureHandler);
-
     mEnvironment.setFrameRateLimit(Settings::Manager::getFloat("framerate limit", "Video"));
 
     prepareEngine (settings);

components/sceneutil/screencapture.cpp

@@ -3,6 +3,7 @@
 #include <components/debug/debuglog.hpp>
 #include <components/sceneutil/workqueue.hpp>
 
+#include <osg/ref_ptr>
 #include <osg/Image>
 #include <osgDB/ReaderWriter>
 #include <osgDB/Registry>
@@ -10,9 +11,43 @@
 #include <boost/filesystem/fstream.hpp>
 #include <boost/filesystem/operations.hpp>
 
-#include <string>
-#include <sstream>
+#include <cassert>
 #include <iomanip>
+#include <sstream>
+#include <string>
+
+namespace
+{
+    class ScreenCaptureWorkItem : public SceneUtil::WorkItem
+    {
+        public:
+            ScreenCaptureWorkItem(const osg::ref_ptr<osgViewer::ScreenCaptureHandler::CaptureOperation>& impl,
+                                  const osg::Image& image, unsigned int contextId)
+                : mImpl(impl),
+                  mImage(new osg::Image(image)),
+                  mContextId(contextId)
+            {
+                assert(mImpl != nullptr);
+            }
+
+            void doWork() override
+            {
+                try
+                {
+                    (*mImpl)(*mImage, mContextId);
+                }
+                catch (const std::exception& e)
+                {
+                    Log(Debug::Error) << "ScreenCaptureWorkItem exception: " << e.what();
+                }
+            }
+
+        private:
+            const osg::ref_ptr<osgViewer::ScreenCaptureHandler::CaptureOperation> mImpl;
+            const osg::ref_ptr<const osg::Image> mImage;
+            const unsigned int mContextId;
+    };
+}
 
 namespace SceneUtil
 {
@@ -70,4 +105,18 @@ namespace SceneUtil
                               << "\", format=\"" << mScreenshotFormat << "\": " << e.what();
         }
     }
+
+    AsyncScreenCaptureOperation::AsyncScreenCaptureOperation(osg::ref_ptr<WorkQueue> queue,
+                                                             osg::ref_ptr<CaptureOperation> impl)
+        : mQueue(std::move(queue)),
+          mImpl(std::move(impl))
+    {
+        assert(mQueue != nullptr);
+        assert(mImpl != nullptr);
+    }
+
+    void AsyncScreenCaptureOperation::operator()(const osg::Image& image, const unsigned int context_id)
+    {
+        mQueue->addWorkItem(new ScreenCaptureWorkItem(mImpl, image, context_id));
+    }
 }

components/sceneutil/screencapture.hpp

@@ -1,6 +1,7 @@
 #ifndef OPENMW_COMPONENTS_SCENEUTIL_SCREENCAPTURE_H
 #define OPENMW_COMPONENTS_SCENEUTIL_SCREENCAPTURE_H
 
+#include <osg/ref_ptr>
 #include <osgViewer/ViewerEventHandlers>
 
 #include <string>
@@ -12,6 +13,8 @@ namespace osg
 
 namespace SceneUtil
 {
+    class WorkQueue;
+
     void writeScreenshotToFile(const std::string& screenshotPath, const std::string& screenshotFormat,
                                const osg::Image& image);
 
@@ -20,12 +23,25 @@ namespace SceneUtil
         public:
             WriteScreenshotToFileOperation(const std::string& screenshotPath, const std::string& screenshotFormat);
 
-            void operator()(const osg::Image& image, const unsigned int /*context_id*/) override;
+            void operator()(const osg::Image& image, const unsigned int context_id) override;
 
         private:
             const std::string mScreenshotPath;
             const std::string mScreenshotFormat;
     };
+
+    class AsyncScreenCaptureOperation : public osgViewer::ScreenCaptureHandler::CaptureOperation
+    {
+        public:
+            AsyncScreenCaptureOperation(osg::ref_ptr<SceneUtil::WorkQueue> queue,
+                                        osg::ref_ptr<osgViewer::ScreenCaptureHandler::CaptureOperation> impl);
+
+            void operator()(const osg::Image& image, const unsigned int context_id) override;
+
+        private:
+            const osg::ref_ptr<SceneUtil::WorkQueue> mQueue;
+            const osg::ref_ptr<osgViewer::ScreenCaptureHandler::CaptureOperation> mImpl;
+    };
 }
 
 #endif