Viewports: fixed an issue where a window manually constrained to the main viewport while crossing over main viewport bounds isn't translated properly. (#7985)

Amend 967073ba3

docs/CHANGELOG.txt

@@ -78,6 +78,8 @@ Other changes:
 
 Docking+Viewports Branch:
 
+- Viewports: fixed an issue where a window manually constrained to the main viewport while crossing
+  over main viewport bounds isn't translated properly. (#7985)
 - Backends: SDL3: added support for viewport->ParentViewportId field to support parenting
   windows at OS level. (#7973) [@RT2code]
 

imgui.cpp

@@ -15224,7 +15224,7 @@ static bool ImGui::UpdateTryMergeWindowIntoHostViewports(ImGuiWindow* window)
 
 // Translate Dear ImGui windows when a Host Viewport has been moved
 // (This additionally keeps windows at the same place when ImGuiConfigFlags_ViewportsEnable is toggled!)
-void ImGui::TranslateWindowsInViewport(ImGuiViewportP* viewport, const ImVec2& old_pos, const ImVec2& new_pos)
+void ImGui::TranslateWindowsInViewport(ImGuiViewportP* viewport, const ImVec2& old_pos, const ImVec2& new_pos, const ImVec2& old_size, const ImVec2& new_size)
 {
     ImGuiContext& g = *GImGui;
     IM_ASSERT(viewport->Window == NULL && (viewport->Flags & ImGuiViewportFlags_CanHostOtherWindows));
@@ -15238,7 +15238,7 @@ void ImGui::TranslateWindowsInViewport(ImGuiViewportP* viewport, const ImVec2& o
     ImRect test_still_fit_rect(old_pos, old_pos + viewport->Size);
     ImVec2 delta_pos = new_pos - old_pos;
     for (ImGuiWindow* window : g.Windows) // FIXME-OPT
-        if (translate_all_windows || (window->Viewport == viewport && test_still_fit_rect.Contains(window->Rect())))
+        if (translate_all_windows || (window->Viewport == viewport && (old_size == new_size || test_still_fit_rect.Contains(window->Rect()))))
             TranslateWindow(window, delta_pos);
 }
 
@@ -15415,7 +15415,7 @@ static void ImGui::UpdateViewportsNewFrame()
         // (This additionally keeps windows at the same place when ImGuiConfigFlags_ViewportsEnable is toggled!)
         const ImVec2 viewport_delta_pos = viewport->Pos - viewport->LastPos;
         if ((viewport->Flags & ImGuiViewportFlags_CanHostOtherWindows) && (viewport_delta_pos.x != 0.0f || viewport_delta_pos.y != 0.0f))
-            TranslateWindowsInViewport(viewport, viewport->LastPos, viewport->Pos);
+            TranslateWindowsInViewport(viewport, viewport->LastPos, viewport->Pos, viewport->LastSize, viewport->Size);
 
         // Update DPI scale
         float new_dpi_scale;
@@ -15525,6 +15525,7 @@ static void ImGui::UpdateViewportsEndFrame()
     {
         ImGuiViewportP* viewport = g.Viewports[i];
         viewport->LastPos = viewport->Pos;
+        viewport->LastSize = viewport->Size;
         if (viewport->LastFrameActive < g.FrameCount || viewport->Size.x <= 0.0f || viewport->Size.y <= 0.0f)
             if (i > 0) // Always include main viewport in the list
                 continue;
@@ -15571,7 +15572,7 @@ ImGuiViewportP* ImGui::AddUpdateViewport(ImGuiWindow* window, ImGuiID id, const
         viewport->ID = id;
         viewport->Idx = g.Viewports.Size;
         viewport->Pos = viewport->LastPos = pos;
-        viewport->Size = size;
+        viewport->Size = viewport->LastSize = size;
         viewport->Flags = flags;
         UpdateViewportPlatformMonitor(viewport);
         g.Viewports.push_back(viewport);

imgui_internal.h

@@ -1968,6 +1968,7 @@ struct ImGuiViewportP : public ImGuiViewport
     int                 LastFocusedStampCount;  // Last stamp number from when a window hosted by this viewport was focused (by comparing this value between two viewport we have an implicit viewport z-order we use as fallback)
     ImGuiID             LastNameHash;
     ImVec2              LastPos;
+    ImVec2              LastSize;
     float               Alpha;                  // Window opacity (when dragging dockable windows/viewports we make them transparent)
     float               LastAlpha;
     bool                LastFocusedHadNavWindow;// Instead of maintaining a LastFocusedWindow (which may harder to correctly maintain), we merely store weither NavWindow != NULL last time the viewport was focused.
@@ -3411,7 +3412,7 @@ namespace ImGui
     IMGUI_API void          CallContextHooks(ImGuiContext* context, ImGuiContextHookType type);
 
     // Viewports
-    IMGUI_API void          TranslateWindowsInViewport(ImGuiViewportP* viewport, const ImVec2& old_pos, const ImVec2& new_pos);
+    IMGUI_API void          TranslateWindowsInViewport(ImGuiViewportP* viewport, const ImVec2& old_pos, const ImVec2& new_pos, const ImVec2& old_size, const ImVec2& new_size);
     IMGUI_API void          ScaleWindowsInViewport(ImGuiViewportP* viewport, float scale);
     IMGUI_API void          DestroyPlatformWindow(ImGuiViewportP* viewport);
     IMGUI_API void          SetWindowViewport(ImGuiWindow* window, ImGuiViewportP* viewport);