Qt5,Qt6: use floating point functions for primitives drawing on scaled displays. issue #41422

lcl/interfaces/qt5/qtobjects.pas

@@ -465,6 +465,7 @@ type
     function getDeviceSize: TPoint;
     function getRegionType(ARegion: QRegionH): integer;
     function getClipRegion: TQtRegion;
+    function preferFloatingPointDrawingFunctions: boolean; {when screen is scaled we use drawLineF, drawRectF etc.}
     procedure setClipping(const AValue: Boolean);
     procedure setClipRect(const ARect: TRect);
     procedure setClipRegion(ARegion: QRegionH; AOperation: QtClipOperation = QtReplaceClip);
@@ -3398,6 +3399,35 @@ begin
   Result := vRegion;
 end;
 
+function TQtDeviceContext.preferFloatingPointDrawingFunctions: boolean;
+const
+  AEpsilon: double = 0.01;
+var
+  APixelRatio: QReal;
+  AWindow: QWindowH;
+  AWidget: QWidgetH;
+  AScreen: QScreenH;
+begin
+  Result := False;
+  if Assigned(Parent) then
+  begin
+    AWindow := QWidget_windowHandle(Parent);
+    if AWindow = nil then
+    begin
+      AWidget := QWidget_topLevelWidget(Parent);
+      AWindow := QWidget_windowHandle(AWidget);
+      if AWindow = nil then
+        exit;
+    end;
+    AScreen := QWindow_screen(AWindow);
+    if AScreen = nil then
+      exit;
+    APixelRatio := QScreen_devicePixelRatio(AScreen);
+    if Abs(APixelRatio - 1.00) > AEpsilon then
+      exit(True);
+  end;
+end;
+
 procedure TQtDeviceContext.setClipping(const AValue: Boolean);
 begin
   QPainter_setClipping(Widget, AValue);

lcl/interfaces/qt5/qtwinapi.inc

@@ -4896,7 +4896,11 @@ begin
       Pt := TQtCustomControl(AHandle).viewport.ScrolledOffset;
       Types.OffsetRect(Rect^, -Pt.X, -Pt.Y);
     end;
-
+    if (Rect^.Width <= 0) or (Rect^.Height <= 0) then
+    begin
+      //DebugLn('WARNING: TQtWidgetSet.InvalidateRect() Rect is null ',dbgs(Rect^),' LCL=',dbgsName(TQtWidget(AHandle).LCLObject));
+      exit(True);
+    end;
     // no need to handle bErase. Qt automatically erase rect on paint event according to docs
     TQtWidget(aHandle).Update(Rect);
   end else
@@ -4966,8 +4970,9 @@ begin
     OldBkMode := SetBkMode(DC, TRANSPARENT);
   if TQtDeviceContext(DC).pen.getCosmetic then
     LastPos := TQtDeviceContext(DC).GetLineLastPixelPos(PenPos, LastPos);
-  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) then
+  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) or
-    TQtDeviceContext(DC).drawLineF(PenPos.X, PenPos.Y, LastPos.X, LastPos.Y)
+    TQtDeviceContext(DC).preferFloatingPointDrawingFunctions then
+      TQtDeviceContext(DC).drawLineF(PenPos.X, PenPos.Y, LastPos.X, LastPos.Y)
   else
     TQtDeviceContext(DC).drawLine(PenPos.X, PenPos.Y, LastPos.X, LastPos.Y);
 
@@ -5321,7 +5326,8 @@ begin
   Result := IsValidDC(DC);
   if Result then
   begin
-    if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) then
+    if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) or
+      TQtDeviceContext(DC).preferFloatingPointDrawingFunctions then
     begin
       GetMem(QtPointsF, NumPts * SizeOf(TQtPointF));
       for i := 0 to NumPts - 1 do
@@ -5407,8 +5413,9 @@ begin
 
   R := NormalizeRect(Rect(X1, Y1, X2, Y2));
   if IsRectEmpty(R) then Exit(True);
-  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) then
+  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) or
-    TQtDeviceContext(DC).drawRectF(R.Left, R.Top, R.Right - R.Left - 1, R.Bottom - R.Top - 1)
+    TQtDeviceContext(DC).preferFloatingPointDrawingFunctions then
+      TQtDeviceContext(DC).drawRectF(R.Left, R.Top, R.Right - R.Left - 1, R.Bottom - R.Top - 1)
   else
     TQtDeviceContext(DC).drawRect(R.Left, R.Top, R.Right - R.Left - 1, R.Bottom - R.Top - 1);
   Result := True;

lcl/interfaces/qt6/qtobjects.pas

@@ -472,6 +472,7 @@ type
     function getDeviceSize: TPoint;
     function getRegionType(ARegion: QRegionH): integer;
     function getClipRegion: TQtRegion;
+    function preferFloatingPointDrawingFunctions: boolean; {when screen is scaled we use drawLineF, drawRectF etc.}
     procedure setClipping(const AValue: Boolean);
     procedure setClipRect(const ARect: TRect);
     procedure setClipRegion(ARegion: QRegionH; AOperation: QtClipOperation = QtReplaceClip);
@@ -3568,6 +3569,25 @@ begin
   Result := vRegion;
 end;
 
+function TQtDeviceContext.preferFloatingPointDrawingFunctions: boolean;
+const
+  AEpsilon: double = 0.01;
+var
+  APixelRatio: QReal;
+  AScreen: QScreenH;
+begin
+  Result := False;
+  if Assigned(Parent) then
+  begin
+    AScreen := QWidget_screen(Parent);
+    if AScreen = nil then
+      exit;
+    APixelRatio := QScreen_devicePixelRatio(AScreen);
+    if Abs(APixelRatio - 1.00) > AEpsilon then
+      exit(True);
+  end;
+end;
+
 procedure TQtDeviceContext.setClipping(const AValue: Boolean);
 begin
   QPainter_setClipping(Widget, AValue);

lcl/interfaces/qt6/qtwinapi.inc

@@ -4924,7 +4924,11 @@ begin
       Pt := TQtCustomControl(AHandle).viewport.ScrolledOffset;
       Types.OffsetRect(Rect^, -Pt.X, -Pt.Y);
     end;
-
+    if (Rect^.Width <= 0) or (Rect^.Height <= 0) then
+    begin
+      //DebugLn('WARNING: TQtWidgetSet.InvalidateRect() Rect is null ',dbgs(Rect^),' LCL=',dbgsName(TQtWidget(AHandle).LCLObject));
+      exit(True);
+    end;
     // no need to handle bErase. Qt automatically erase rect on paint event according to docs
     TQtWidget(aHandle).Update(Rect);
   end else
@@ -4994,8 +4998,9 @@ begin
     OldBkMode := SetBkMode(DC, TRANSPARENT);
   if TQtDeviceContext(DC).pen.getCosmetic then
     LastPos := TQtDeviceContext(DC).GetLineLastPixelPos(PenPos, LastPos);
-  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) then
+  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) or
-    TQtDeviceContext(DC).drawLineF(PenPos.X, PenPos.Y, LastPos.X, LastPos.Y)
+    TQtDeviceContext(DC).preferFloatingPointDrawingFunctions then
+      TQtDeviceContext(DC).drawLineF(PenPos.X, PenPos.Y, LastPos.X, LastPos.Y)
   else
     TQtDeviceContext(DC).drawLine(PenPos.X, PenPos.Y, LastPos.X, LastPos.Y);
   if TQtDeviceContext(DC).pen.getStyle = QtCustomDashLine then
@@ -5393,7 +5398,8 @@ begin
   Result := IsValidDC(DC);
   if Result then
   begin
-    if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) then
+    if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) or
+      TQtDeviceContext(DC).preferFloatingPointDrawingFunctions then
     begin
       GetMem(QtPointsF, NumPts * SizeOf(TQtPointF));
       for i := 0 to NumPts - 1 do
@@ -5479,8 +5485,9 @@ begin
 
   R := NormalizeRect(Rect(X1, Y1, X2, Y2));
   if IsRectEmpty(R) then Exit(True);
-  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) then
+  if QPainter_testRenderHint(TQtDeviceContext(DC).Widget, QPainterAntialiasing) or
-    TQtDeviceContext(DC).drawRectF(R.Left, R.Top, R.Right - R.Left - 1, R.Bottom - R.Top - 1)
+    TQtDeviceContext(DC).preferFloatingPointDrawingFunctions then
+      TQtDeviceContext(DC).drawRectF(R.Left, R.Top, R.Right - R.Left - 1, R.Bottom - R.Top - 1)
   else
     TQtDeviceContext(DC).drawRect(R.Left, R.Top, R.Right - R.Left - 1, R.Bottom - R.Top - 1);
   Result := True;