Merge branch 'feature/query-old-ogl-version' into 'develop'

Fixed version query for ogl < 3.0

See merge request !88

glfw/glow-extras/glfw/GlfwContext.cc

@@ -78,11 +78,36 @@ GlfwContext::GlfwContext()
 #define GL_CALL
 #endif
 
-    using glGetIntegerFunc = void GL_CALL(GLenum, GLint*);
-    auto getGlInt = reinterpret_cast<glGetIntegerFunc*>(glfwGetProcAddress("glGetIntegerv"));
-    GLint gmajor, gminor;
-    getGlInt(GL_MAJOR_VERSION, &gmajor);
-    getGlInt(GL_MINOR_VERSION, &gminor);
+    using glGetStringFunc = GLubyte* GL_CALL(GLenum);
+    auto getString = reinterpret_cast<glGetStringFunc*>(glfwGetProcAddress("glGetString"));
+
+    // taken from glad
+    GLint gmajor;
+    GLint gminor;
+
+    const char* version;
+    const char* prefixes[] = {"OpenGL ES-CM ", "OpenGL ES-CL ", "OpenGL ES ", NULL};
+
+    version = (const char*)getString(GL_VERSION);
+    if (!version)
+        return;
+
+    for (auto i = 0; prefixes[i]; i++)
+    {
+        const size_t length = strlen(prefixes[i]);
+        if (strncmp(version, prefixes[i], length) == 0)
+        {
+            version += length;
+            break;
+        }
+    }
+
+#ifdef _MSC_VER
+    sscanf_s(version, "%d.%d", &gmajor, &gminor);
+#else
+    sscanf(version, "%d.%d", &gmajor, &gminor);
+#endif
+
     if (gmajor * 10 + gminor < 33)
     {
         std::cerr << "OpenGL Version below 3.3. Trying to get at least 3.3." << std::endl;