Windows: fixed SetNextWindowCollapsed()/SetWindowCollapsed() breaking codepath that preserve last contents size when collapsed. (#7691)

Author: ocornut

docs/CHANGELOG.txt

@@ -48,6 +48,10 @@ Other changes:
 
 - IO: variations in analog-only components of gamepad events do not interfere
   with trickling of mouse position events (#4921, #8508)
+- Windows: fixed SetNextWindowCollapsed()/SetWindowCollapsed() breaking
+  codepath that preserve last contents size when collapsed, resulting in
+  programmatically uncollapsing auto-sizing windows having them flicker size
+  for a frame. (#7691) [@achabense]
 - Error Handling: added better error report and recovery for extraneous
   EndPopup() call. (#1651, #8499)
 - Style, InputText: added ImGuiCol_InputTextCursor to configure color of

imgui.cpp

@@ -8228,8 +8228,10 @@ void ImGui::SetWindowCollapsed(ImGuiWindow* window, bool collapsed, ImGuiCond co
         return;
     window->SetWindowCollapsedAllowFlags &= ~(ImGuiCond_Once | ImGuiCond_FirstUseEver | ImGuiCond_Appearing);
 
-    // Set
-    window->Collapsed = collapsed;
+    // Queue applying in Begin()
+    if (window->WantCollapseToggle)
+        window->Collapsed ^= 1;
+    window->WantCollapseToggle = (window->Collapsed != collapsed);
 }
 
 void ImGui::SetWindowHitTestHole(ImGuiWindow* window, const ImVec2& pos, const ImVec2& size)