--- c:\src\JVCL3_45\run\JvPrvwDoc.pas	2011-10-12 08:42:22.514938000 -0400
+++ JvPrvwDoc.pas	2012-10-01 14:42:08.863987600 -0400
@@ -276,6 +276,7 @@
     FOnOptionsChange: TNotifyEvent;
     FOnScrollHint: TJvScrollHintEvent;
     FSelection: TJvPreviewSelection;
+    FAccumulatedWheelDelta: Integer;
     procedure DoOptionsChange(Sender: TObject);
     procedure DoDeviceInfoChange(Sender: TObject);
     procedure DoScaleModeChange(Sender: TObject);
@@ -961,8 +962,8 @@
     Inc(SI.fMask, SIF_DISABLENOSCROLL);
   GetScrollInfo(Handle, SB_HORZ, SI);
 
-  SI.nMax := FMaxWidth - ClientWidth;
-  SI.nPage := 0;
+  SI.nMax := FMaxWidth - 1;
+  SI.nPage := Min(ClientWidth, SI.nMax - SI.nMin + 1);
   ShowScrollBar(Handle, SB_HORZ, not HideScrollBars and (ScrollBars in [ssHorizontal, ssBoth]));
   SetScrollInfo(Handle, SB_HORZ, SI, True);
   // update scroll pos if it has changed
@@ -987,8 +988,8 @@
   end
   else
   begin
-    SI.nMax := FMaxHeight - ClientHeight;
-    SI.nPage := 0; // FMaxHeight div TotalRows;
+    SI.nMax := FMaxHeight - 1;
+    SI.nPage := Min(ClientHeight, SI.nMax - SI.nMin + 1);
   end;
   ShowScrollBar(Handle, SB_VERT, not HideScrollBars and (ScrollBars in [ssVertical, ssBoth]));
   SetScrollInfo(Handle, SB_VERT, SI, True);
@@ -1319,11 +1320,12 @@
     SB_ENDSCROLL:
       Exit;
   end;
-  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax);
+  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax - Max(SI.nPage - 1, 0));
   if Assigned(FOnHorzScroll) then
     FOnHorzScroll(Self, TScrollCode(Msg.ScrollCode), NewPos);
-  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax);
-  ScrollBy(-FScrollPos.X + NewPos, 0);
+  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax - Max(SI.nPage - 1, 0));
+  // Old versions of JVCL called ScrollBy, but it's redundant with SetScrollInfo.
+  //ScrollBy(-FScrollPos.X + NewPos, 0);
   FScrollPos.X := NewPos;
   SI.nPos := NewPos;
   SetScrollInfo(Handle, SB_HORZ, SI, True);
@@ -1335,11 +1337,18 @@
 procedure TJvCustomPreviewControl.WMVScroll(var Msg: TWMVScroll);
 var
   SI: TScrollInfo;
-  NewPos, Increment: Integer;
+  NewPos, Increment, PageIncrement: Integer;
 begin
-  Increment := FPageHeight + Integer(Options.VertSpacing);
-  if not IsPageMode then
-    Increment := Increment div 3;
+  if IsPageMode then
+  Begin
+    Increment := FPageHeight + Integer(Options.VertSpacing);
+    PageIncrement := Increment;
+  End
+  Else
+  Begin
+    Increment := 50;
+    PageIncrement := ClientHeight - Increment;
+  End;
   if Increment < 1 then
     Increment := 1;
 
@@ -1352,10 +1361,14 @@
       NewPos := 0;
     SB_BOTTOM:
       NewPos := FMaxHeight;
-    SB_LINEDOWN, SB_PAGEDOWN:
+    SB_LINEDOWN:
       NewPos := FScrollPos.Y + Increment;
-    SB_LINEUP, SB_PAGEUP:
+    SB_PAGEDOWN:
+      NewPos := FScrollPos.Y + PageIncrement;
+    SB_LINEUP:
       NewPos := FScrollPos.Y - Increment;
+    SB_PAGEUP:
+      NewPos := FScrollPos.Y - PageIncrement;
     SB_THUMBPOSITION, SB_THUMBTRACK:
       begin
         NewPos := SI.nTrackPos;
@@ -1371,11 +1384,12 @@
         Exit;
       end;
   end;
-  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax);
+  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax - Max(SI.nPage - 1, 0));
   if Assigned(FOnVertScroll) then
     FOnVertScroll(Self, TScrollCode(Msg.ScrollCode), NewPos);
-  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax);
-  ScrollBy(0, -FScrollPos.Y + NewPos);
+  NewPos := EnsureRange(NewPos, SI.nMin, SI.nMax - Max(SI.nPage - 1, 0));
+  // Old versions of JVCL called ScrollBy, but it's redundant with SetScrollInfo.
+  //ScrollBy(0, -FScrollPos.Y + NewPos);
   FScrollPos.Y := NewPos;
   SI.nPos := NewPos;
   SetScrollInfo(Handle, SB_VERT, SI, True);
@@ -1737,6 +1751,8 @@
 var
   Msg: TWMScroll;
   SI: TScrollInfo;
+  WheelScrollLines: Integer;
+  DeltaPerLine: Integer;
 begin
   Result := inherited DoMouseWheel(Shift, WheelDelta, MousePos);
   if not Result then
@@ -1747,15 +1763,40 @@
     GetScrollInfo(Handle, SB_VERT, SI);
     if SI.nMax = 0 then
       Exit;
+
+    SystemParametersInfo(SPI_GETWHEELSCROLLLINES, 0, @WheelScrollLines, 0);
+    FAccumulatedWheelDelta := FAccumulatedWheelDelta + WheelDelta;
+
     Msg.Msg := WM_VSCROLL;
-    if WheelDelta > 0 then
-      Msg.ScrollCode := SB_PAGEUP
+    if (WheelScrollLines = -1) Or IsPageMode then
+    begin
+      DeltaPerLine := 120;
+      if WheelDelta > 0 then
+        Msg.ScrollCode := SB_PAGEUP
+      else
+        Msg.ScrollCode := SB_PAGEDOWN;
+    end
     else
-      Msg.ScrollCode := SB_PAGEDOWN;
-    Msg.Pos := FScrollPos.Y;
-    Msg.Result := 0;
-    WMVScroll(Msg);
-    Refresh;
+    begin
+      DeltaPerLine := 120 div WheelScrollLines;
+      if WheelDelta > 0 then
+        Msg.ScrollCode := SB_LINEUP
+      else
+        Msg.ScrollCode := SB_LINEDOWN;
+    end;
+
+    while abs(FAccumulatedWheelDelta) >= DeltaPerLine do
+    begin
+      Msg.Pos := FScrollPos.Y;
+      Msg.Result := 0;
+      WMVScroll(Msg);
+      
+      if FAccumulatedWheelDelta > 0 then
+        FAccumulatedWheelDelta := FAccumulatedWheelDelta - DeltaPerLine
+      else
+        FAccumulatedWheelDelta := FAccumulatedWheelDelta + DeltaPerLine;
+    end;
+
     TDeactiveHintThread.Create(500, HintWindow);
     HintWindow := nil;
     Result := True;