Move declaration of IVideoCapture class into precomp.hpp, make some methods of…

Move declaration of IVideoCapture class into precomp.hpp, make some methods of IVideoCapture pure virtual

modules/highgui/include/opencv2/highgui.hpp

@@ -531,17 +531,7 @@ enum { CAP_INTELPERC_DEPTH_MAP              = 0, // Each pixel is a 16-bit integ
      };
 
 
-class IVideoCapture
-{
-public:
-    virtual ~IVideoCapture() {}
-    virtual double getProperty(int) { return 0; }
-    virtual bool setProperty(int, double) { return 0; }
-    virtual bool grabFrame() { return true; }
-    virtual bool retrieveFrame(int, cv::OutputArray) { return 0; }
-    virtual int getCaptureDomain() { return CAP_ANY; } // Return the type of the capture object: CAP_VFW, etc...
-};
-
+class IVideoCapture;
 class CV_EXPORTS_W VideoCapture
 {
 public:

modules/highgui/src/precomp.hpp

@@ -196,6 +196,20 @@ double cvGetRatioWindow_GTK(const char* name);
 double cvGetOpenGlProp_W32(const char* name);
 double cvGetOpenGlProp_GTK(const char* name);
 
+namespace cv
+{
+    class IVideoCapture
+    {
+    public:
+        virtual ~IVideoCapture() {}
+        virtual double getProperty(int) { return 0; }
+        virtual bool setProperty(int, double) { return 0; }
+        virtual bool grabFrame() = 0;
+        virtual bool retrieveFrame(int, cv::OutputArray) = 0;
+        virtual int getCaptureDomain() { return CAP_ANY; } // Return the type of the capture object: CAP_VFW, etc...
+    };
+};
+
 //for QT
 #if defined (HAVE_QT)
 double cvGetModeWindow_QT(const char* name);