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

examples/example_glut_opengl2/main.cpp

@@ -76,7 +76,7 @@ void glut_display_func()
     ImGui::Render();
     ImGuiIO& io = ImGui::GetIO();
     glViewport(0, 0, (GLsizei)io.DisplaySize.x, (GLsizei)io.DisplaySize.y);
-    glClearColor(clear_color.x, clear_color.y, clear_color.z, clear_color.w);
+    glClearColor(clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w);
     glClear(GL_COLOR_BUFFER_BIT);
     //glUseProgram(0); // You may want this if using this code in an OpenGL 3+ context where shaders may be bound, but prefer using the GL3+ code.
     ImGui_ImplOpenGL2_RenderDrawData(ImGui::GetDrawData());