Comments to redirect people to OpenGL3 examples (#1116)

examples/README.txt

@@ -8,10 +8,11 @@ Third party languages and frameworks bindings: https://github.com/ocornut/imgui/
 
 TL;DR; 
  - Newcomers, read 'PROGRAMMER GUIDE' in imgui.cpp for notes on how to setup ImGui in your codebase.
- - Refer to 'opengl2_example' to LEARN how the library is setup, it is the simplest one.
+ - To LEARN how the library is setup, you may refer to 'opengl2_example' because is the simplest one.
    The other examples requires more boilerplate and are harder to read.
- - If you are using OpenGL in your application, probably use an opengl3_xxx backend. 
+   However, USE 'opengl3_example' in your application if you are using any modern OpenGL3+ calls.
-   Mixing old fixed pipeline OpenGL2 and programmable pipeline OpenGL3+ isn't well supported by drivers.
+   Mixing old fixed pipeline OpenGL2 and programmable pipeline OpenGL3+ isn't well supported by some drivers.
+   If you are not sure, in doubt, use 'opengl3_example'.
  - If you are using of the backend provided here, so you can copy the imgui_impl_xxx.cpp/h files
    to your project and use them unmodified.
  - If you have your own engine, you probably want to start from one of the OpenGL example and adapt it to 
@@ -44,14 +45,17 @@ Also note that some setup or GPU drivers may be causing extra lag (possibly by e
 leaving you with no option but sadness/anger (Intel GPU drivers were reported as such).
 
 opengl2_example/
-    GLFW + OpenGL example (old fixed pipeline).
+    GLFW + OpenGL example (old, fixed graphic pipeline).
-    This is simple to read. Prefer following this example to learn how ImGui works!
+    This is only provided as a reference to learn how ImGui integration works, because it is easier to read.
+    However, if your code is using GL3+ context, using this may confuse your driver. Please use the GL3 example below.
 	(You might be able to use this code in a GL3/GL4 context but make sure you disable the programmable 
-	pipeline by calling "glUseProgram(0)" before ImGui::Render.)
+	pipeline by calling "glUseProgram(0)" before ImGui::Render. It appears that many librairies and drivers
+	are having issues mixing GL2 calls and newer GL3/GL4 calls. So it isn't recommended that you use that.)
 
 opengl3_example/
     GLFW + OpenGL example (programmable pipeline, binding modern functions with GL3W).
-    This uses more modern OpenGL calls and custom shaders. It's more messy.
+    This uses more modern OpenGL calls and custom shaders. 
+    Prefer using that if you are using modern OpenGL3/4 in your application.
 
 directx9_example/
     DirectX9 example, Windows only.

examples/opengl2_example/imgui_impl_glfw.cpp

@@ -1,9 +1,10 @@
 // ImGui GLFW binding with OpenGL
 // In this binding, ImTextureID is used to store an OpenGL 'GLuint' texture identifier. Read the FAQ about ImTextureID in imgui.cpp.
 
-// If your context is GL3/GL3 then prefer using the code in opengl3_example.
+// If your context or own usage of OpenGL involve anything GL3/GL4, prefer using the code in opengl3_example.
+// If you are not sure what that means, prefer using the code in opengl3_example.
 // You *might* use this code with a GL3/GL4 context but make sure you disable the programmable pipeline by calling "glUseProgram(0)" before ImGui::Render().
-// We cannot do that from GL2 code because the function doesn't exist. 
+// We cannot do that from GL2 code because the function doesn't exist. Mixing GL2 calls and GL3/GL4 calls is giving trouble to many librairies/drivers.
 
 // You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
 // If you use this binding you'll need to call 4 functions: ImGui_ImplXXXX_Init(), ImGui_ImplXXXX_NewFrame(), ImGui::Render() and ImGui_ImplXXXX_Shutdown().

examples/sdl_opengl2_example/imgui_impl_sdl.cpp

@@ -1,6 +1,9 @@
 // ImGui SDL2 binding with OpenGL
 // In this binding, ImTextureID is used to store an OpenGL 'GLuint' texture identifier. Read the FAQ about ImTextureID in imgui.cpp.
 
+// If your context or own usage of OpenGL involve anything GL3/GL4, prefer using the code in sdl_opengl3_example.
+// If you are not sure what that means, prefer using the code in sdl_opengl3_example.
+
 // You can copy and use unmodified imgui_impl_* files in your project. See main.cpp for an example of using this.
 // If you use this binding you'll need to call 4 functions: ImGui_ImplXXXX_Init(), ImGui_ImplXXXX_NewFrame(), ImGui::Render() and ImGui_ImplXXXX_Shutdown().
 // If you are new to ImGui, see examples/README.txt and documentation at the top of imgui.cpp.