Fix horizontal scrolling to not be reversed on tilt wheel mice and old Thinkp...

webkit/glue/webinputevent_win.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "webkit/glue/webinputevent.h"
 
 #include "base/logging.h"
 #include "base/string_util.h"
@@ skipping 145 matching lines @@
         break;
       case SB_PAGEDOWN:
         wheel_delta = -1;
         scroll_by_page = true;
         break;
       default:  // We don't supoprt SB_THUMBPOSITION or SB_THUMBTRACK here.
         wheel_delta = 0;
         break;
     }
 
-    if (message == WM_HSCROLL) {
+    if (message == WM_HSCROLL)
       horizontal_scroll = true;
-      wheel_delta = -wheel_delta;
-    }
   } else {
     // Non-synthesized event; we can just read data off the event.
     get_key_state = GetKeyState;
     key_state = GET_KEYSTATE_WPARAM(wparam);
 
     global_x = static_cast<short>(LOWORD(lparam));
     global_y = static_cast<short>(HIWORD(lparam));
 
     wheel_delta = static_cast<float>(GET_WHEEL_DELTA_WPARAM(wparam));
-    if (((message == WM_MOUSEHWHEEL) || (key_state & MK_SHIFT)) &&
-        (wheel_delta != 0))
+    if (message == WM_MOUSEHWHEEL) {
       horizontal_scroll = true;
+      wheel_delta = -wheel_delta;  // Windows is <- -/+ ->, WebKit <- +/- ->.
+    }
   }
+  if (key_state & MK_SHIFT)
+    horizontal_scroll = true;
 
   // Set modifiers based on key state.
   if (key_state & MK_SHIFT)
     modifiers |= SHIFT_KEY;
   if (key_state & MK_CONTROL)
     modifiers |= CTRL_KEY;
   if (get_key_state(VK_MENU) & 0x8000)
     modifiers |= (ALT_KEY | META_KEY);
 
   // Set coordinates by translating event coordinates from screen to client.
@@ skipping 23 matching lines @@
     unsigned long scroll_lines = kDefaultScrollLinesPerWheelDelta;
     SystemParametersInfo(SPI_GETWHEELSCROLLLINES, 0, &scroll_lines, 0);
     if (scroll_lines == WHEEL_PAGESCROLL)
       scroll_by_page = true;
     if (!scroll_by_page) {
       scroll_delta *=
           static_cast<float>(scroll_lines) * kScrollbarPixelsPerLine;
     }
   }
 
-  // Set scroll amount based on above calculations.
+  // Set scroll amount based on above calculations.  WebKit expects positive
+  // delta_y to mean "scroll up" and positive delta_x to mean "scroll left".
   if (horizontal_scroll) {
     delta_x = scroll_delta;
     delta_y = 0;
   } else {
     delta_x = 0;
     delta_y = scroll_delta;
   }
 }
 
 // WebKeyboardEvent -----------------------------------------------------------
@@ skipping 93 matching lines @@
     modifiers |= CTRL_KEY;
   if (GetKeyState(VK_MENU) & 0x8000)
     modifiers |= (ALT_KEY | META_KEY);
 
   if (LOWORD(lparam) > 1)
     modifiers |= IS_AUTO_REPEAT;
   if (IsKeyPad(wparam, lparam))
     modifiers |= IS_KEYPAD;
 }