fixed eye blinking in vector graphics examples

modules/v4d/samples/vector_graphics.cpp

@@ -13,7 +13,9 @@ int main() {
             //Calls from this namespace may only be used inside a nvg context
             using namespace cv::v4d::nvg;
             clear();
-            float t = cv::getTickCount() / cv::getTickFrequency();
+
+            static long start = cv::getTickCount() / cv::getTickFrequency();
+            float t = cv::getTickCount() / cv::getTickFrequency() - start;
             float x = 0;
             float y = 0;
             float w = sz.width / 4;

modules/v4d/samples/vector_graphics_and_fb.cpp

@@ -6,16 +6,19 @@ using namespace cv::v4d;
 
 int main() {
     Ptr<V4D> window = V4D::make(Size(1280, 720), cv::Size(), "Vector Graphics and Framebuffer");
-
+#ifdef __EMSCRIPTEN__
+    float start = emscripten_get_now() / 1000.0f;
+#endif
     //Render the framebuffer in the native window in an endless loop
     window->run([=]() {
         //Creates a NanoVG context and draws eyes
-        window->nvg([](const Size& sz) {
+        window->nvg([=](const Size& sz) {
             //Calls from this namespace may only be used inside a nvg context
             using namespace cv::v4d::nvg;
             clear();
 
-            float t = cv::getTickCount() / cv::getTickFrequency();
+            static long start = cv::getTickCount() / cv::getTickFrequency();
+            float t = cv::getTickCount() / cv::getTickFrequency() - start;
             float x = 0;
             float y = 0;
             float w = sz.width / 4;