fixed flicker in native builds

modules/v4d/src/detail/framebuffercontext.cpp

@@ -693,6 +693,7 @@ void FrameBufferContext::begin(GLenum framebufferTarget) {
 }
 
 void FrameBufferContext::end() {
+    this->makeCurrent();
     GL_CHECK(glFlush());
 }
 

modules/v4d/src/detail/nanoguicontext.cpp

@@ -71,6 +71,7 @@ void NanoguiContext::render(bool print, bool graphical) {
             {
 #ifndef __EMSCRIPTEN__
                 mainFbContext_.makeCurrent();
+                GL_CHECK(glFinish());
                 GL_CHECK(glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0));
                 GL_CHECK(glViewport(0, 0, mainFbContext_.getWindowSize().width, mainFbContext_.getWindowSize().height));
                 glClear(GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
@@ -109,6 +110,8 @@ void NanoguiContext::render(bool print, bool graphical) {
             {
 #ifdef __EMSCRIPTEN__
                 FrameBufferContext::GLScope glScope(fbCtx(), GL_FRAMEBUFFER);
+#else
+                GL_CHECK(glFinish());
 #endif
                 screen().draw_widgets();
             }

modules/v4d/src/v4d.cpp

@@ -548,6 +548,7 @@ bool V4D::display() {
             nguiCtx().render(printFPS_, showFPS_);
 #endif
             fbCtx().makeCurrent();
+            GL_CHECK(glFinish());
 #ifndef __EMSCRIPTEN__
             glfwSwapBuffers(fbCtx().getGLFWWindow());
 #else