marge r50991 #b61461e71a,r50994,r51003:

LCL: fixed infinite loop and crash with TScrollingWinControl. issue #29194
LCL: add support of scrolling invisible window. issue #29194
Qt: keep track of scrolled offset when viewport is not visible. issue #29239

git-svn-id: branches/fixes_1_6@51007 -

lcl/include/controlscrollbar.inc

@@ -73,6 +73,7 @@ begin
   PrevPosition := FPosition;
   // position has to be set before FControl.ScrollBy !!!
   FPosition := Value;
+
   // scroll logical client area of FControl
   if Kind = sbVertical then
     FControl.ScrollBy(0, PrevPosition - FPosition)

lcl/include/wincontrol.inc

@@ -6136,10 +6136,10 @@ end;
 
 procedure TWinControl.ScrollBy_WS(DeltaX, DeltaY: Integer);
 begin
-  if HandleAllocated and IsWindowVisible(Handle) then
+  if HandleAllocated then
     TWSWinControlClass(WidgetSetClass).ScrollBy(Self, DeltaX, DeltaY)
   else
-    ScrollBy(DeltaX, DeltaY);
+    raise Exception.Create('TWinControl.ScrollBy_WS: Handle not allocated');
 end;
 
 procedure TWinControl.ScrollBy(DeltaX, DeltaY: Integer);

lcl/interfaces/qt/qtwidgets.pas

@@ -473,9 +473,14 @@ type
   { TQtViewPort }
   
   TQtViewPort = class(TQtWidget)
+  private
+    {when our viewport is invisible then we must keep track of scrolling. issue #29239}
+    FInvisibleX: integer;
+    FInvisibleY: integer;
   public
     function CanPaintBackground: Boolean; override;
     function EventFilter(Sender: QObjectH; Event: QEventH): Boolean; cdecl; override;
+    procedure InitializeWidget; override;
     procedure scroll(dx, dy: integer; ARect: PRect = nil); override;
     procedure stackUnder(AWidget: QWidgetH); override;
   end;
@@ -16085,6 +16090,18 @@ begin
       ' Event=', EventTypeToStr(Event),' inUpdate=',inUpdate);
   {$endif}
   case QEvent_type(Event) of
+    QEventShow,
+    QEventShowToParent:
+    begin
+      {Qt does not track scrolled offset of widget when it''s not visible.issue #29239}
+      if (FInvisibleX <> 0) or (FInvisibleY <> 0) then
+      begin
+        QWidget_scroll(Widget, FInvisibleX, FInvisibleY);
+        FInvisibleX := 0;
+        FInvisibleY := 0;
+      end;
+      Result := inherited EventFilter(Sender, Event);
+    end;
     QEventResize:
     begin
       // immediate update clientRect !
@@ -16167,9 +16184,21 @@ begin
   end;
 end;
 
+procedure TQtViewPort.InitializeWidget;
+begin
+  FInvisibleX := 0;
+  FInvisibleY := 0;
+  inherited InitializeWidget;
+end;
+
 procedure TQtViewPort.scroll(dx, dy: integer; ARect: PRect = nil);
 begin
-  inherited scroll(dx, dy, ARect);
+  if not getVisible then
+  begin
+    FInvisibleX += dx;
+    FInvisibleY += dy;
+  end else
+    inherited scroll(dx, dy, ARect);
   FScrollX := FScrollX + dx;
   FScrollY := FScrollY + dy;
 end;

lcl/interfaces/win32/win32wscontrols.pp

@@ -590,7 +590,7 @@ end;
 class procedure TWin32WSWinControl.ScrollBy(const AWinControl: TWinControl;
   DeltaX, DeltaY: integer);
 begin
-  if Windows.IsWindowVisible(AWinControl.Handle) then
+  if AWinControl.HandleAllocated then
     ScrollWindowEx(AWinControl.Handle, DeltaX, DeltaY, nil, nil, 0, nil, SW_INVALIDATE or SW_ERASE or SW_SCROLLCHILDREN);
 end;