Merge branch 'master' into docking

# Conflicts:
#	backends/imgui_impl_dx10.cpp
#	backends/imgui_impl_dx11.cpp
#	backends/imgui_impl_dx12.cpp
#	backends/imgui_impl_dx9.cpp
#	backends/imgui_impl_opengl3.cpp
#	backends/imgui_impl_win32.cpp
#	docs/CHANGELOG.txt
#	examples/example_glfw_vulkan/main.cpp
#	examples/example_sdl_vulkan/main.cpp
#	imgui.cpp

backends/imgui_impl_opengl2.cpp

@@ -92,6 +92,7 @@ static void ImGui_ImplOpenGL2_SetupRenderState(ImDrawData* draw_data, int fb_wid
     // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, vertex/texcoord/color pointers, polygon fill.
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+    //glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA); // In order to composite our output buffer we need to preserve alpha
     glDisable(GL_CULL_FACE);
     glDisable(GL_DEPTH_TEST);
     glDisable(GL_STENCIL_TEST);