Window: Fixed SetNextWindowSizeConstraints() with non-rounded positio…

…ns making windows drift. (#2067, #2530)

docs/CHANGELOG.txt

@@ -68,6 +68,7 @@ Other Changes:
   highlight from parent menu items earlier than necessary while approaching the child menu.
 - Window: Close button is horizontally aligned with style.FramePadding.x.
 - Window: Fixed contents region being off by WindowBorderSize amount on the right when scrollbar is active.
+- Window: Fixed SetNextWindowSizeConstraints() with non-rounded positions making windows drift. (#2067, 2530)
 - Popups: Closing a popup restores the focused/nav window in place at the time of the popup opening,
   instead of restoring the window that was in the window stack at the time of the OpenPopup call. (#2517)
   Among other things, this allows opening a popup while no window are focused, and pressing Escape to

imgui.cpp

@@ -4648,6 +4648,8 @@ static ImVec2 CalcSizeAfterConstraint(ImGuiWindow* window, ImVec2 new_size)
             g.NextWindowData.SizeCallback(&data);
             new_size = data.DesiredSize;
         }
+        new_size.x = ImFloor(new_size.x);
+        new_size.y = ImFloor(new_size.y);
     }
 
     // Minimum size

imgui.h

@@ -269,7 +269,7 @@ namespace ImGui
     // Prefer using SetNextXXX functions (before Begin) rather that SetXXX functions (after Begin).
     IMGUI_API void          SetNextWindowPos(const ImVec2& pos, ImGuiCond cond = 0, const ImVec2& pivot = ImVec2(0,0)); // set next window position. call before Begin(). use pivot=(0.5f,0.5f) to center on given point, etc.
     IMGUI_API void          SetNextWindowSize(const ImVec2& size, ImGuiCond cond = 0);                  // set next window size. set axis to 0.0f to force an auto-fit on this axis. call before Begin()
-    IMGUI_API void          SetNextWindowSizeConstraints(const ImVec2& size_min, const ImVec2& size_max, ImGuiSizeCallback custom_callback = NULL, void* custom_callback_data = NULL); // set next window size limits. use -1,-1 on either X/Y axis to preserve the current size. Use callback to apply non-trivial programmatic constraints.
+    IMGUI_API void          SetNextWindowSizeConstraints(const ImVec2& size_min, const ImVec2& size_max, ImGuiSizeCallback custom_callback = NULL, void* custom_callback_data = NULL); // set next window size limits. use -1,-1 on either X/Y axis to preserve the current size. Sizes will be rounded down. Use callback to apply non-trivial programmatic constraints.
     IMGUI_API void          SetNextWindowContentSize(const ImVec2& size);                               // set next window content size (~ enforce the range of scrollbars). not including window decorations (title bar, menu bar, etc.). set an axis to 0.0f to leave it automatic. call before Begin()
     IMGUI_API void          SetNextWindowCollapsed(bool collapsed, ImGuiCond cond = 0);                 // set next window collapsed state. call before Begin()
     IMGUI_API void          SetNextWindowFocus();                                                       // set next window to be focused / front-most. call before Begin()