Use Qt's High-DPI scaling on Windows (#4868)

src/widgets/BaseWindow.hpp

@@ -75,7 +75,6 @@ public:
     bool applyLastBoundsCheck();
 
     float scale() const override;
-    float qtFontScale() const;
 
     /// @returns true if the window is the top-most window.
     ///          Either #setTopMost was called or the `TopMost` flag is set which overrides this
@@ -132,7 +131,6 @@ private:
     void drawCustomWindowFrame(QPainter &painter);
     void onFocusLost();
 
-    bool handleDPICHANGED(MSG *msg);
     bool handleSHOWWINDOW(MSG *msg);
     bool handleSIZE(MSG *msg);
     bool handleMOVE(MSG *msg);
@@ -149,8 +147,6 @@ private:
     bool frameless_;
     bool shown_ = false;
     FlagsEnum<Flags> flags_;
-    float nativeScale_ = 1;
-    bool isResizeFixing_ = false;
     bool isTopMost_ = false;
 
     struct {
@@ -168,6 +164,7 @@ private:
     widgets::BoundsChecking lastBoundsCheckMode_ = widgets::BoundsChecking::Off;
 
 #ifdef USEWINSDK
+    void updateRealSize();
     /// @brief Returns the HWND of this window if it has one
     ///
     /// A QWidget only has an HWND if it has been created. Before that,
@@ -193,6 +190,10 @@ private:
     QTimer useNextBounds_;
     bool isNotMinimizedOrMaximized_{};
     bool lastEventWasNcMouseMove_ = false;
+    /// The real bounds of the window as returned by
+    /// GetWindowRect. Used for drawing.
+    QRect realBounds_;
+    bool isMaximized_ = false;
 #endif
 
     pajlada::Signals::SignalHolder connections_;