Viewport: Refactored ViewportFlagsOverrideMask+ViewportFlagsOverrideValue into ViewportFlagsOverrideSet+ViewportFlagsOverrideClear which appears easier to grasp. (#1542)

(cherry picked from commit 9437630872e7ca19065bee78fcafaab54a0d5bf2)

imgui.cpp

@@ -6162,8 +6162,10 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
                 window->Viewport->ParentViewportId = parent_window_in_stack->Viewport->ID;
             else
                 window->Viewport->ParentViewportId = g.IO.ConfigViewportsNoDefaultParent ? 0 : IMGUI_VIEWPORT_DEFAULT_ID;
-            if (window->WindowClass.ViewportFlagsOverrideMask)
-                viewport_flags = (viewport_flags & ~window->WindowClass.ViewportFlagsOverrideMask) | (window->WindowClass.ViewportFlagsOverrideValue & window->WindowClass.ViewportFlagsOverrideMask);
+            if (window->WindowClass.ViewportFlagsOverrideSet)
+                viewport_flags |= window->WindowClass.ViewportFlagsOverrideSet;
+            if (window->WindowClass.ViewportFlagsOverrideClear)
+                viewport_flags &= ~window->WindowClass.ViewportFlagsOverrideClear;
 
             // We also tell the back-end that clearing the platform window won't be necessary, as our window is filling the viewport and we have disabled BgAlpha
             viewport_flags |= ImGuiViewportFlags_NoRendererClear;
@@ -7437,6 +7439,7 @@ void ImGui::SetNextWindowDockID(ImGuiID id, ImGuiCond cond)
 void ImGui::SetNextWindowClass(const ImGuiWindowClass* window_class)
 {
     ImGuiContext& g = *GImGui;
+    IM_ASSERT((window_class->ViewportFlagsOverrideSet & window_class->ViewportFlagsOverrideClear) == 0); // Cannot set both set and clear for the same bit
     g.NextWindowData.Flags |= ImGuiNextWindowDataFlags_HasWindowClass;
     g.NextWindowData.WindowClass = *window_class;
 }
@@ -10291,7 +10294,7 @@ static bool ImGui::GetWindowAlwaysWantOwnViewport(ImGuiWindow* window)
 {
     // Tooltips and menus are not automatically forced into their own viewport when the NoMerge flag is set, however the multiplication of viewports makes them more likely to protrude and create their own.
     ImGuiContext& g = *GImGui;
-    if (g.IO.ConfigViewportsNoAutoMerge || ((window->WindowClass.ViewportFlagsOverrideValue & window->WindowClass.ViewportFlagsOverrideMask) & ImGuiViewportFlags_NoAutoMerge))
+    if (g.IO.ConfigViewportsNoAutoMerge || (window->WindowClass.ViewportFlagsOverrideSet & ImGuiViewportFlags_NoAutoMerge))
         if (g.ConfigFlagsForFrame & ImGuiConfigFlags_ViewportsEnable)
             if (!window->DockIsActive)
                 if ((window->Flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) == 0)

imgui.h

@@ -1588,12 +1588,12 @@ struct ImGuiWindowClass
 {
     ImGuiID             ClassId;                    // User data. 0 = Default class (unclassed)
     ImGuiID             ParentViewportId;           // Hint for the platform back-end. If non-zero, the platform back-end can create a parent<>child relationship between the platform windows. Not conforming back-ends are free to e.g. parent every viewport to the main viewport or not.
-    ImGuiViewportFlags  ViewportFlagsOverrideMask;  // Viewport flags to override when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
-    ImGuiViewportFlags  ViewportFlagsOverrideValue; // Viewport flags values to override when a window of this class owns a viewport.
+    ImGuiViewportFlags  ViewportFlagsOverrideSet;   // Viewport flags to set when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
+    ImGuiViewportFlags  ViewportFlagsOverrideClear; // Viewport flags to clear when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
     bool                DockingAlwaysTabBar;        // Set to true to enforce windows of this class always having their own tab (equivalent of setting the global io.ConfigDockingAlwaysTabBar)
     bool                DockingAllowUnclassed;      // Set to true to allow windows of this class to be docked/merged with an unclassed window.
 
-    ImGuiWindowClass() { ClassId = 0; ParentViewportId = 0; ViewportFlagsOverrideMask = ViewportFlagsOverrideValue = 0x00; DockingAlwaysTabBar = false; DockingAllowUnclassed = true; }
+    ImGuiWindowClass() { ClassId = 0; ParentViewportId = 0; ViewportFlagsOverrideSet = ViewportFlagsOverrideClear = 0x00; DockingAlwaysTabBar = false; DockingAllowUnclassed = true; }
 };
 
 // Data payload for Drag and Drop operations: AcceptDragDropPayload(), GetDragDropPayload()