Examples: OpenGL2: Extra comments (#606)

examples/opengl_example/imgui_impl_glfw.cpp

@@ -1,6 +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.
+// 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. 
+
 // 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.

examples/opengl_example/imgui_impl_glfw.h

@@ -1,6 +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.
+// 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. 
+
 // 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.