Viewport: Comment to suggest making WindowBg opaque when viewports are enabled.

examples/example_glfw_opengl3/main.cpp

@@ -97,10 +97,13 @@ int main(int, char**)
     ImGui_ImplOpenGL3_Init(glsl_version);
 
     // Setup Style
-    ImGui::GetStyle().WindowRounding = 0.0f;
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();
 
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.WindowRounding = 0.0f;                                // When viewports are enabled it is preferable to disable WinodwRounding
+    style.Colors[ImGuiCol_WindowBg].w = 1.0f;                   // When viewports are enabled it is preferable to disable WindowBg alpha
+
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them.
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple.

examples/example_sdl_opengl3/main.cpp

@@ -91,6 +91,10 @@ int main(int, char**)
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();
 
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.WindowRounding = 0.0f;                                // When viewports are enabled it is preferable to disable WinodwRounding
+    style.Colors[ImGuiCol_WindowBg].w = 1.0f;                   // When viewports are enabled it is preferable to disable WindowBg alpha
+
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them. 
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple. 

examples/example_win32_directx11/main.cpp

@@ -145,10 +145,13 @@ int main(int, char**)
     ImGui_ImplDX11_Init(g_pd3dDevice, g_pd3dDeviceContext);
 
     // Setup Style
-    ImGui::GetStyle().WindowRounding = 0.0f;
     ImGui::StyleColorsDark();
     //ImGui::StyleColorsClassic();
 
+    ImGuiStyle& style = ImGui::GetStyle();
+    style.WindowRounding = 0.0f;                                // When viewports are enabled it is preferable to disable WinodwRounding
+    style.Colors[ImGuiCol_WindowBg].w = 1.0f;                   // When viewports are enabled it is preferable to disable WindowBg alpha
+
     // Load Fonts
     // - If no fonts are loaded, dear imgui will use the default font. You can also load multiple fonts and use ImGui::PushFont()/PopFont() to select them. 
     // - AddFontFromFileTTF() will return the ImFont* so you can store it if you need to select the font among multiple. 

imgui.h

@@ -891,6 +891,7 @@ enum ImGuiConfigFlags_
     ImGuiConfigFlags_NoMouseCursorChange    = 1 << 5,   // Instruct back-end to not alter mouse cursor shape and visibility. Use if the back-end cursor changes are interfering with yours and you don't want to use SetMouseCursor() to change mouse cursor. You may want to honor requests from imgui by reading GetMouseCursor() yourself instead.
 
     // [BETA] Viewports
+    // When using viewports it is recommended that your default value for ImGuiCol_WindowBg is opaque (Alpha=1.0) so transition to a viewport won't be noticeable.
     ImGuiConfigFlags_ViewportsEnable        = 1 << 10,  // Viewport enable flags (require both ImGuiConfigFlags_PlatformHasViewports + ImGuiConfigFlags_RendererHasViewports set by the respective back-ends)
     ImGuiConfigFlags_ViewportsNoTaskBarIcon = 1 << 11,  // Disable task bars icons for all secondary viewports (will set ImGuiViewportFlags_NoTaskBarIcon on them)
     ImGuiConfigFlags_ViewportsNoMerge       = 1 << 12,  // All floating windows will always create their own viewport and platform window.