From e9c686e8043571be9e537005d4eeaa596274cd3e Mon Sep 17 00:00:00 2001
From: ondrej <ondrej@lazarus-ide.org>
Date: Thu, 24 Mar 2016 15:24:14 +0000
Subject: [PATCH] win32: forward unhandled mousewheel messages to parent in
 order to support scrolling when mouse cursor is on child wincontrol.

git-svn-id: trunk@52045 -
---
 lcl/forms.pp                         |  1 -
 lcl/include/scrollingwincontrol.inc  | 12 -----------
 lcl/interfaces/win32/win32winapi.inc | 31 +++++++++++++++++++++++-----
 3 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/lcl/forms.pp b/lcl/forms.pp
index ec28a4e724..e7400f5c0e 100644
--- a/lcl/forms.pp
+++ b/lcl/forms.pp
@@ -168,7 +168,6 @@ type
     procedure WMSize(var Message: TLMSize); message LM_Size;
     procedure WMHScroll(var Message : TLMHScroll); message LM_HScroll;
     procedure WMVScroll(var Message : TLMVScroll); message LM_VScroll;
-    procedure WMMouseWheel(var Message: TLMMouseEvent); message LM_MOUSEWHEEL;
     procedure ComputeScrollbars; virtual;
     procedure SetAutoScroll(Value: Boolean); virtual;
     procedure Loaded; override;
diff --git a/lcl/include/scrollingwincontrol.inc b/lcl/include/scrollingwincontrol.inc
index dbc678735f..16ac326337 100644
--- a/lcl/include/scrollingwincontrol.inc
+++ b/lcl/include/scrollingwincontrol.inc
@@ -304,18 +304,6 @@ begin
   HorzScrollbar.ScrollHandler(Message);
 end;
 
-procedure TScrollingWinControl.WMMouseWheel(var Message: TLMMouseEvent);
-begin
-  // support VertScrollBar.Increment on Windows.
-  // The code has no meaning on other OS because scrolling is handled there directly by the OS
-  if Mouse.WheelScrollLines > 0 then
-    Message.WheelDelta :=
-      (Min(High(Message.WheelDelta), Max(Low(Message.WheelDelta),
-        (VertScrollBar.Increment * Message.WheelDelta))) div 120) * 120;
-
-  inherited WMMouseWheel(Message);
-end;
-
 constructor TScrollingWinControl.Create(TheOwner : TComponent);
 begin
   Inherited Create(TheOwner);
diff --git a/lcl/interfaces/win32/win32winapi.inc b/lcl/interfaces/win32/win32winapi.inc
index 7b5f755b13..4891224c67 100644
--- a/lcl/interfaces/win32/win32winapi.inc
+++ b/lcl/interfaces/win32/win32winapi.inc
@@ -165,6 +165,10 @@ var
     ScrollMsg, ScrollBar: dword;
     ScrollOffset: integer;
     Pos: TPoint;
+    MouseMessage: TLMMouseEvent;
+    SW: TScrollingWinControl;
+    SB: TControlScrollBar;
+    ScrollWheelDelta: LongInt;
   begin
     if not TWinControl(Sender).HandleAllocated then
       exit;
@@ -208,15 +212,30 @@ var
       ScrollBar := SB_VERT;
       ScrollMsg := WM_VSCROLL;
     end;
-    if Windows.GetScrollInfo(Handle, ScrollBar, ScrollInfo) then
+    if Windows.GetScrollInfo(Handle, ScrollBar, ScrollInfo)
+    and (Int64(ScrollInfo.nPage) < Int64(ScrollInfo.nMax)) then
     begin
-      with TLMMouseEvent(Message) do
+      MouseMessage := TLMMouseEvent(Message);
       begin
         if Mouse.WheelScrollLines < 0 then
           // -1 means, scroll one page
-          ScrollOffset := (WheelDelta * integer(ScrollInfo.nPage)) div 120
+          ScrollOffset := (MouseMessage.WheelDelta * integer(ScrollInfo.nPage)) div 120
         else
-          ScrollOffset := (WheelDelta * Mouse.WheelScrollLines) div 120;
+          if Sender is TScrollingWinControl then // support scrollbar increment
+          begin
+            SW := TScrollingWinControl(Sender);
+            if ScrollBar = SB_Horz then
+              SB := SW.HorzScrollBar
+            else
+              SB := SW.VertScrollBar;
+            ScrollWheelDelta :=
+              (Min(High(MouseMessage.WheelDelta), Max(Low(MouseMessage.WheelDelta),
+                (SB.Increment * MouseMessage.WheelDelta))) div 120) * 120;
+          end else
+            ScrollWheelDelta := MouseMessage.WheelDelta;
+        begin
+          ScrollOffset := (ScrollWheelDelta * Mouse.WheelScrollLines) div 120;
+        end;
         WParam := Windows.WParam(ScrollInfo.nPos - ScrollOffset);
         if WParam > ScrollInfo.nMax - integer(ScrollInfo.nPage) + 1 then
           WParam := ScrollInfo.nMax - integer(ScrollInfo.nPage) + 1;
@@ -225,7 +244,9 @@ var
         WParam := SB_THUMBPOSITION or (WParam shl 16);
       end;
       Windows.PostMessage(Handle, ScrollMsg, WParam, HWND(nil));
-    end;
+    end else
+    if (TControl(Sender).Parent <> nil) then
+      TControl(Sender).Parent.WindowProc(TLMessage(Message));
   end;
 
 begin