raise minimal OpenGL version to 3.2 compat

modules/viz2d/include/opencv2/viz2d/viz2d.hpp

@@ -168,7 +168,7 @@ public:
      */
     CV_EXPORTS static cv::Ptr<Viz2D> make(const cv::Size& initialSize,
             const cv::Size& frameBufferSize, bool offscreen, const string& title, int major = 3,
-            int minor = 0, int samples = 0, bool debug = false);
+            int minor = 2, int samples = 0, bool debug = false);
     /*!
      * Default destructor
      */
@@ -427,7 +427,7 @@ private:
      * @param debug Create a debug OpenGL context.
      */
     CV_EXPORTS Viz2D(const cv::Size& initialSize, const cv::Size& frameBufferSize, bool offscreen,
-            const string& title, int major = 3, int minor = 0, int samples = 0, bool debug = false);
+            const string& title, int major = 3, int minor = 2, int samples = 0, bool debug = false);
     void setDefaultKeyboardEventCallback();
     void setKeyboardEventCallback(
             std::function<bool(int key, int scancode, int action, int modifiers)> fn);

modules/viz2d/src/detail/nanovgcontext.cpp

@@ -26,7 +26,34 @@ void NanoVGContext::render(std::function<void(const cv::Size&)> fn) {
     cv::viz::nvg::detail::NVG::initializeContext(context_), fn(clglContext_.getSize());
 }
 
+void push() {
+#ifndef VIZ2D_USE_ES3
+    GL_CHECK(glPushClientAttrib(GL_CLIENT_ALL_ATTRIB_BITS));
+    GL_CHECK(glPushAttrib(GL_ALL_ATTRIB_BITS));
+    GL_CHECK(glMatrixMode(GL_MODELVIEW));
+    GL_CHECK(glPushMatrix());
+    GL_CHECK(glMatrixMode(GL_PROJECTION));
+    GL_CHECK(glPushMatrix());
+    GL_CHECK(glMatrixMode(GL_TEXTURE));
+    GL_CHECK(glPushMatrix());
+#endif
+}
+
+void pop() {
+#ifndef VIZ2D_USE_ES3
+    GL_CHECK(glMatrixMode(GL_TEXTURE));
+    GL_CHECK(glPopMatrix());
+    GL_CHECK(glMatrixMode(GL_PROJECTION));
+    GL_CHECK(glPopMatrix());
+    GL_CHECK(glMatrixMode(GL_MODELVIEW));
+    GL_CHECK(glPopMatrix());
+    GL_CHECK(glPopClientAttrib());
+    GL_CHECK(glPopAttrib());
+#endif
+}
+
 void NanoVGContext::begin() {
+    push();
     float w = v2d_.getFrameBufferSize().width;
     float h = v2d_.getFrameBufferSize().height;
     float r = v2d_.getXPixelRatio();
@@ -43,6 +70,7 @@ void NanoVGContext::end() {
     //FIXME make nvgCancelFrame possible
     nvgEndFrame(context_);
     nvgRestore(context_);
+    pop();
 }
 }
 }

modules/viz2d/src/viz2d.cpp

@@ -132,8 +132,8 @@ bool Viz2D::initializeWindowing() {
 #else
     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, major_);
     glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, minor_);
+    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);
     glfwWindowHint(GLFW_CONTEXT_CREATION_API, GLFW_EGL_CONTEXT_API);
-    glfwWindowHint (GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
     glfwWindowHint(GLFW_CLIENT_API, GLFW_OPENGL_API) ;
 #endif
     glfwWindowHint(GLFW_SAMPLES, samples_);