ovis: add support for off-screen windows

modules/ovis/include/opencv2/ovis.hpp

@@ -25,7 +25,9 @@ enum SceneSettings
     /// draw coordinate system crosses for debugging
     SCENE_SHOW_CS_CROSS = 4,
     /// Apply anti-aliasing. The first window determines the setting for all windows.
-    SCENE_AA = 8
+    SCENE_AA = 8,
+    /// Render off-screen without a window. Allows separate AA setting. Requires manual update via @ref WindowScene::update
+    SCENE_OFFSCREEN = 16
 };
 
 enum MaterialProperty
@@ -276,6 +278,10 @@ public:
     CV_WRAP virtual void setCameraIntrinsics(InputArray K, const Size& imsize,
                                              float zNear = -1,
                                              float zFar = -1) = 0;
+    /**
+     * render this window, but do not swap buffers. Automatically called by @ref ovis::waitKey
+     */
+    CV_WRAP virtual void update() = 0;
 };
 
 /**

modules/ovis/src/ovis.cpp

@@ -289,7 +289,7 @@ class WindowSceneImpl : public WindowScene
     Root* root;
     SceneManager* sceneMgr;
     SceneNode* camNode;
-    RenderWindow* rWin;
+    RenderTarget* rWin;
     Ptr<OgreBites::CameraMan> camman;
     Ptr<Rectangle2D> bgplane;
     std::unordered_map<AnimationState*, Controller<Real>*> frameCtrlrs;
@@ -344,11 +344,22 @@ public:
 
         if (!app->sceneMgr)
         {
+            CV_Assert((flags & SCENE_OFFSCREEN) == 0 && "off-screen rendering for main window not supported");
+
             app->sceneMgr = sceneMgr;
             rWin = app->getRenderWindow();
             if (camman)
                 app->addInputListener(camman.get());
         }
+        else if (flags & SCENE_OFFSCREEN)
+        {
+            // render into an offscreen texture
+            TexturePtr tex = TextureManager::getSingleton().createManual(
+                title, RESOURCEGROUP_NAME, TEX_TYPE_2D, sz.width, sz.height, 0, PF_BYTE_RGB,
+                TU_RENDERTARGET, NULL, false, flags & SCENE_AA ? 4 : 0);
+            rWin = tex->getBuffer()->getRenderTarget();
+            rWin->setAutoUpdated(false); // only update when requested
+        }
         else
         {
             OgreBites::NativeWindowPair nwin = app->createWindow(title, sz.width, sz.height);
@@ -820,6 +831,11 @@ public:
         ndc = (2 * f * n) / ndc;
     }
 
+    void update()
+    {
+        rWin->update(false);
+    }
+
     void fixCameraYawAxis(bool useFixed, InputArray _up) CV_OVERRIDE
     {
 #if OGRE_VERSION >= ((1 << 16) | (11 << 8) | 5)