Viewport: Added ImGuiConfigFlags_ViewportsDecoration to re-enable platform decoration (#1542)

docs/TODO.txt

@@ -281,6 +281,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
 
  - examples: move ImGui::NewFrame() out of the backend _NewFrame() ?
  - viewport: make it possible to have no main/hosting viewport
+ - viewport: with platform decoration enabled, platform may force constraint (e.g. minimum size)
  - viewport: use getfocus/setfocus api to synchronize imgui<>platform focus better (e.g imgui-side ctrl-tab can focus os window, OS initial setup and alt-tab can focus imgui window etc.)
  - viewport: store per-viewport/monitor DPI in .ini file so an application reload or main window changing DPI on reload can be properly patched for.
  - viewport: vulkan renderer implementation. 

imgui.cpp

@@ -3211,10 +3211,13 @@ void ImGui::NewFrame()
     {
         if ((g.IO.BackendFlags & ImGuiBackendFlags_PlatformHasViewports) && (g.IO.BackendFlags & ImGuiBackendFlags_RendererHasViewports))
         {
-            IM_ASSERT((g.FrameCount == 0 || g.FrameCount == g.FrameCountPlatformEnded) && "Forgot to call UpdatePlatformWindows() at the end of the previous frame?");
+            IM_ASSERT((g.FrameCount == 0 || g.FrameCount == g.FrameCountPlatformEnded) && "Forgot to call UpdatePlatformWindows() in main loop after EndFrame()?");
             IM_ASSERT(g.PlatformIO.Platform_CreateWindow != NULL  && "Platform init didn't install handlers?");
             IM_ASSERT(g.PlatformIO.Platform_DestroyWindow != NULL && "Platform init didn't install handlers?");
             IM_ASSERT(g.PlatformIO.Platform_GetWindowPos != NULL  && "Platform init didn't install handlers?");
+            IM_ASSERT(g.PlatformIO.Platform_SetWindowPos != NULL  && "Platform init didn't install handlers?");
+            IM_ASSERT(g.PlatformIO.Platform_GetWindowSize != NULL  && "Platform init didn't install handlers?");
+            IM_ASSERT(g.PlatformIO.Platform_SetWindowSize != NULL  && "Platform init didn't install handlers?");
             IM_ASSERT((g.Viewports[0]->PlatformUserData != NULL || g.Viewports[0]->PlatformHandle != NULL) && "Platform init didn't setup main viewport.");
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
             IM_ASSERT(g.IO.RenderDrawListsFn == NULL);  // Call ImGui::Render() then pass ImGui::GetDrawData() yourself to your render function!
@@ -5028,7 +5031,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             {
                 // Late create viewport, based on the assumption that with our calculations, the DPI will be known ahead (same as the DPI of the selection done in UpdateSelectWindowViewport)
                 //ImGuiViewport* old_viewport = window->Viewport;
-                ImGuiViewportFlags viewport_flags = ImGuiViewportFlags_NoDecoration | ImGuiViewportFlags_NoFocusOnAppearing | ((window->Flags & ImGuiWindowFlags_NoInputs) ? ImGuiViewportFlags_NoInputs : 0);
+                ImGuiViewportFlags viewport_flags = ImGuiViewportFlags_NoFocusOnAppearing | ((window->Flags & ImGuiWindowFlags_NoInputs) ? ImGuiViewportFlags_NoInputs : 0);
                 window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, viewport_flags);
 
                 // FIXME-DPI
@@ -7191,6 +7194,7 @@ static ImGuiViewportP* FindViewportHoveredFromPlatformWindowStack(const ImVec2 m
     return best_candidate;
 }
 
+// Called in NewFrame()
 static void ImGui::UpdateViewports()
 {
     ImGuiContext& g = *GImGui;
@@ -7413,7 +7417,7 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         {
             window->Viewport = FindViewportByID(window->ViewportId);
             if (window->Viewport == NULL && window->ViewportPos.x != FLT_MAX && window->ViewportPos.y != FLT_MAX)
-                window->Viewport = AddUpdateViewport(window, window->ID, window->ViewportPos, window->Size, ImGuiViewportFlags_NoDecoration);
+                window->Viewport = AddUpdateViewport(window, window->ID, window->ViewportPos, window->Size, ImGuiViewportFlags_None);
         }
     }
 
@@ -7443,11 +7447,11 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
         bool leave_host_viewport = has_viewport && !own_viewport && !window->Viewport->GetRect().Contains(window->Rect());
         bool move_from_own_viewport = has_viewport && own_viewport && !(window->Viewport->Flags & ImGuiViewportFlags_NoInputs);
         if (!has_viewport || leave_host_viewport || move_from_own_viewport)
-            window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoDecoration | ImGuiViewportFlags_NoFocusOnAppearing | ImGuiViewportFlags_NoInputs);
+            window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoFocusOnAppearing | ImGuiViewportFlags_NoInputs);
     }
     else if (GetWindowAlwaysWantOwnViewport(window))
     {
-        window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_NoDecoration);
+        window->Viewport = AddUpdateViewport(window, window->ID, window->Pos, window->Size, ImGuiViewportFlags_None);
     }
 
     // Mark window as allowed to protrude outside of its viewport and into the current monitor
@@ -7472,16 +7476,15 @@ static void ImGui::UpdateSelectWindowViewport(ImGuiWindow* window)
 
     // Update flags
     window->ViewportOwned = (window == window->Viewport->Window);
-    if (window->ViewportOwned)
-        window->Viewport->Flags |= ImGuiViewportFlags_NoDecoration;
 
     // If the OS window has a title bar, hide our imgui title bar
-    if (window->ViewportOwned && !(window->Viewport->Flags & ImGuiViewportFlags_NoDecoration))
+    //if (window->ViewportOwned && !(window->Viewport->Flags & ImGuiViewportFlags_NoDecoration))
-        window->Flags |= ImGuiWindowFlags_NoTitleBar;
+    //    window->Flags |= ImGuiWindowFlags_NoTitleBar;
 
     window->ViewportId = window->Viewport->ID;
 }
 
+// Called by imgui at the end of the main loop, after EndFrame()
 void ImGui::UpdatePlatformWindows()
 {
     ImGuiContext& g = *GImGui;
@@ -7515,13 +7518,17 @@ void ImGui::UpdatePlatformWindows()
         if (viewport->Size.x <= 0 || viewport->Size.y <= 0)
             continue;
 
-        // Update viewport flags
+        // Update common viewport flags for owned viewports
         if (viewport->Window != NULL)
         {
-            bool topmost = (viewport->Window->Flags & ImGuiWindowFlags_Tooltip) != 0;
+            ImGuiViewportFlags flags = viewport->Flags & ~(ImGuiViewportFlags_TopMost | ImGuiViewportFlags_NoTaskBarIcon | ImGuiViewportFlags_NoDecoration);
-            bool no_task_bar_icon = (g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsNoTaskBarIcons) != 0 || (viewport->Window->Flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0;
+            if (viewport->Window->Flags & ImGuiWindowFlags_Tooltip)
-            viewport->Flags = topmost ? (viewport->Flags | ImGuiViewportFlags_TopMost) : (viewport->Flags & ~ImGuiViewportFlags_TopMost);
+                flags |= ImGuiViewportFlags_TopMost;
-            viewport->Flags = no_task_bar_icon ? (viewport->Flags | ImGuiViewportFlags_NoTaskBarIcon) : (viewport->Flags & ~ImGuiViewportFlags_NoTaskBarIcon);
+            if ((g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsNoTaskBarIcon) != 0 || (viewport->Window->Flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0)
+                flags |= ImGuiViewportFlags_NoTaskBarIcon;
+            if ((g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsDecoration) == 0 || (viewport->Window->Flags & (ImGuiWindowFlags_ChildMenu | ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_Popup)) != 0)
+                flags |= ImGuiViewportFlags_NoDecoration;
+            viewport->Flags = flags;
         }
 
         // Create window

imgui.h

@@ -886,10 +886,11 @@ enum ImGuiConfigFlags_
 
     // [BETA] Viewports
     ImGuiConfigFlags_ViewportsEnable        = 1 << 10,  // Viewport enable flags (require both ImGuiConfigFlags_PlatformHasViewports + ImGuiConfigFlags_RendererHasViewports set by the respective back-ends)
-    ImGuiConfigFlags_ViewportsNoTaskBarIcons= 1 << 11,  // Disable task bars icons for all secondary viewports (will set ImGuiViewportFlags_NoTaskBarIcon on them)
+    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.
-    ImGuiConfigFlags_DpiEnableScaleViewports= 1 << 13,  // FIXME-DPI: Reposition and resize imgui windows when the DpiScale of a viewport changed (mostly useful for the main viewport hosting other window). Note that resizing the main window itself is up to your application.
+    ImGuiConfigFlags_ViewportsDecoration    = 1 << 13,  // FIXME [Broken] Enable platform decoration for all secondary viewports (will not set ImGuiViewportFlags_NoDecoration on them). This currently doesn't behave well in Windows because 1) By default the new window animation get in the way of our transitions, 2) It enable a minimum window size which tends to breaks resizing. You can workaround the later by setting style.WindowMinSize to a bigger value.
-    ImGuiConfigFlags_DpiEnableScaleFonts    = 1 << 14,  // FIXME-DPI: Request bitmap-scaled fonts to match DpiScale. This is a very low-quality workaround. The correct way to handle DPI is _currently_ to replace the atlas and/or fonts in the Platform_OnChangedViewport callback, but this is all early work in progress.
+    ImGuiConfigFlags_DpiEnableScaleViewports= 1 << 14,  // FIXME-DPI: Reposition and resize imgui windows when the DpiScale of a viewport changed (mostly useful for the main viewport hosting other window). Note that resizing the main window itself is up to your application.
+    ImGuiConfigFlags_DpiEnableScaleFonts    = 1 << 15,  // FIXME-DPI: Request bitmap-scaled fonts to match DpiScale. This is a very low-quality workaround. The correct way to handle DPI is _currently_ to replace the atlas and/or fonts in the Platform_OnChangedViewport callback, but this is all early work in progress.
 
     // User storage (to allow your back-end/engine to communicate to code that may be shared between multiple projects. Those flags are not used by core ImGui)
     ImGuiConfigFlags_IsSRGB                 = 1 << 20,  // Application is SRGB-aware.
@@ -2068,7 +2069,8 @@ struct ImGuiPlatformIO
 // Flags stored in ImGuiViewport::Flags, giving indications to the platform back-ends
 enum ImGuiViewportFlags_
 {
-    ImGuiViewportFlags_NoDecoration             = 1 << 0,   // Platform Window: Disable platform title bar, borders, etc.
+    ImGuiViewportFlags_None                     = 0,
+    ImGuiViewportFlags_NoDecoration             = 1 << 0,   // Platform Window: Disable platform decorations: title bar, borders, etc.
     ImGuiViewportFlags_NoFocusOnAppearing       = 1 << 1,   // Platform Window: Don't take focus when created.
     ImGuiViewportFlags_NoInputs                 = 1 << 2,   // Platform Window: Make mouse pass through so we can drag this window while peaking behind it.
     ImGuiViewportFlags_NoTaskBarIcon            = 1 << 3,   // Platform Window: Disable platform task bar icon (for popups, menus, or all windows if ImGuiConfigFlags_ViewportsNoTaskBarIcons if set)
@@ -2088,9 +2090,9 @@ struct ImGuiViewport
 
     void*               PlatformUserData;       // void* to hold custom data structure for the platform (e.g. windowing info, render context)
     void*               PlatformHandle;         // void* for FindViewportByPlatformHandle(). (e.g. suggested to use natural platform handle such as HWND, GlfwWindow*, SDL_Window*)
-    bool                PlatformRequestClose;   // Platform window requested closure
+    bool                PlatformRequestClose;   // Platform window requested closure (e.g. window was moved by the OS / host window manager, e.g. pressing ALT-F4)
-    bool                PlatformRequestMove;    // Platform window requested move (e.g. window was moved by the OS / host window manager)
+    bool                PlatformRequestMove;    // Platform window requested move (e.g. window was moved by the OS / host window manager, authoritative position will be OS window position)
-    bool                PlatformRequestResize;  // Platform window requested resize (e.g. window was resize by the OS / host window manager)
+    bool                PlatformRequestResize;  // Platform window requested resize (e.g. window was resized by the OS / host window manager, authoritative size will be OS window size)
     void*               RendererUserData;       // void* to hold custom data structure for the renderer (e.g. swap chain, frame-buffers etc.)
 
     ImGuiViewport()     { ID = 0; Flags = 0; DpiScale = 0.0f; DrawData = NULL; PlatformUserData = PlatformHandle = NULL; PlatformRequestClose = PlatformRequestMove = PlatformRequestResize = false; RendererUserData = NULL; }

imgui_demo.cpp

@@ -312,8 +312,10 @@ void ImGui::ShowDemoWindow(bool* p_open)
             ImGui::SameLine(); ShowHelpMarker("Instruct back-end to not alter mouse cursor shape and visibility.");
             ImGui::CheckboxFlags("io.ConfigFlags: ViewportsEnable", (unsigned int *)&io.ConfigFlags, ImGuiConfigFlags_ViewportsEnable);
             ImGui::SameLine(); ShowHelpMarker("Toggling this at runtime is normally unsupported (it will offset your windows).");
-            ImGui::CheckboxFlags("io.ConfigFlags: ViewportsNoTaskBarIcons", (unsigned int *)&io.ConfigFlags, ImGuiConfigFlags_ViewportsNoTaskBarIcons);
+            ImGui::CheckboxFlags("io.ConfigFlags: ViewportsNoTaskBarIcon", (unsigned int *)&io.ConfigFlags, ImGuiConfigFlags_ViewportsNoTaskBarIcon);
             ImGui::SameLine(); ShowHelpMarker("Toggling this at runtime is normally unsupported (most platform back-ends won't refresh the task bar icon state right away).");
+            ImGui::CheckboxFlags("io.ConfigFlags: ViewportsDecoration", (unsigned int *)&io.ConfigFlags, ImGuiConfigFlags_ViewportsDecoration);
+            ImGui::SameLine(); ShowHelpMarker("Toggling this at runtime is normally unsupported (most platform back-ends won't refresh the decoration right away).");
             ImGui::CheckboxFlags("io.ConfigFlags: ViewportsNoMerge", (unsigned int *)&io.ConfigFlags, ImGuiConfigFlags_ViewportsNoMerge);
             ImGui::SameLine(); ShowHelpMarker("All floating windows will always create their own viewport and platform window.");
             ImGui::Checkbox("io.ConfigInputTextCursorBlink", &io.ConfigInputTextCursorBlink);