Convert from line scrolling to pixel scrolling. Increase pixel scroll amount on Windows.

See also https://bugs.webkit.org/show_bug.cgi?id=24407 .

BUG=6172
Review URL: http://codereview.chromium.org/40241

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@11151 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 26 insertions, 18 deletions

diff --git a/webkit/glue/event_conversion.cc b/webkit/glue/event_conversion.cc
index 21259ff..a54f908 100644
--- a/webkit/glue/event_conversion.cc
+++ b/webkit/glue/event_conversion.cc
@@ -127,7 +127,7 @@ MakePlatformWheelEvent::MakePlatformWheelEvent(Widget* widget,
   m_deltaY = e.delta_y;
   m_isAccepted = false;
   m_granularity = e.scroll_by_page ?
-      ScrollByPageWheelEvent : ScrollByLineWheelEvent;
+      ScrollByPageWheelEvent : ScrollByPixelWheelEvent;
   m_shiftKey = (e.modifiers & WebInputEvent::SHIFT_KEY) != 0;
   m_ctrlKey = (e.modifiers & WebInputEvent::CTRL_KEY) != 0;
   m_altKey = (e.modifiers & WebInputEvent::ALT_KEY) != 0;
diff --git a/webkit/glue/webinputevent_linux.cc b/webkit/glue/webinputevent_linux.cc
index 12fb179..799bbb2 100644
--- a/webkit/glue/webinputevent_linux.cc
+++ b/webkit/glue/webinputevent_linux.cc
@@ -123,22 +123,22 @@ WebMouseWheelEvent::WebMouseWheelEvent(const GdkEventScroll* event) {
   // - Gtk makes the scroll amount a function of the size of the scroll bar,
   //   which is not available to us here.
   // Instead, we pick a number that empirically matches Firefox's behavior.
-  static const float kWheelDelta = 4;
+  static const float kScrollbarPixelsPerTick = 160.0f / 3.0f;
 
   delta_x = 0;
   delta_y = 0;
   switch (event->direction) {
     case GDK_SCROLL_UP:
-      delta_y = kWheelDelta;
+      delta_y = kScrollbarPixelsPerTick;
       break;
     case GDK_SCROLL_DOWN:
-      delta_y = -kWheelDelta;
+      delta_y = -kScrollbarPixelsPerTick;
       break;
     case GDK_SCROLL_LEFT:
-      delta_x = kWheelDelta;
+      delta_x = kScrollbarPixelsPerTick;
       break;
     case GDK_SCROLL_RIGHT:
-      delta_x = -kWheelDelta;
+      delta_x = -kScrollbarPixelsPerTick;
       break;
     default:
       break;
diff --git a/webkit/glue/webinputevent_mac.mm b/webkit/glue/webinputevent_mac.mm
index f713683..bcf9c5f 100644
--- a/webkit/glue/webinputevent_mac.mm
+++ b/webkit/glue/webinputevent_mac.mm
@@ -35,8 +35,6 @@
 #undef LOG
 #include "base/logging.h"
 
-static const unsigned long kDefaultScrollLinesPerWheelDelta = 3;
-
 // WebMouseEvent --------------------------------------------------------------
 
 WebMouseEvent::WebMouseEvent(NSEvent *event, NSView* view) {
@@ -136,14 +134,13 @@ WebMouseWheelEvent::WebMouseWheelEvent(NSEvent *event, NSView* view) {
   x = location.x;
   y = [view frame].size.height - location.y;  // flip y
 
-  // Convert wheel delta amount to a number of lines to scroll.
+  // Convert wheel delta amount to a number of pixels to scroll.
+  static const float kScrollbarPixelsPerTick = 40.0f;
   float wheel_delta = [event deltaY];
-  const float delta_lines = wheel_delta * kDefaultScrollLinesPerWheelDelta;
+  const float delta_lines = wheel_delta * kScrollbarPixelsPerTick;
 
   // Set scroll amount based on above calculations.
   if ([event modifierFlags] & NSShiftKeyMask) {
-    // Scrolling up should move left, scrolling down should move right.  This is
-    // opposite Safari, but seems more consistent with vertical scrolling.
     delta_x = delta_lines;
     delta_y = 0;
   } else {
diff --git a/webkit/glue/webinputevent_win.cc b/webkit/glue/webinputevent_win.cc
index 455ecfc..8c82901 100644
--- a/webkit/glue/webinputevent_win.cc
+++ b/webkit/glue/webinputevent_win.cc
@@ -195,25 +195,36 @@ WebMouseWheelEvent::WebMouseWheelEvent(HWND hwnd,
   x = client_point.x;
   y = client_point.y;
 
-  // Convert wheel delta amount to a number of lines/chars to scroll.
+  // Convert wheel delta amount to a number of pixels to scroll.
+  //
+  // How many pixels should we scroll per line?  Gecko uses the height of the
+  // current line, which means scroll distance changes as you go through the
+  // page or go to different pages.  IE 7 is ~50 px/line, although the value
+  // seems to vary slightly by page and zoom level.  Since IE 7 has a smoothing
+  // algorithm on scrolling, it can get away with slightly larger scroll values
+  // without feeling jerky.  Here we use 100 px per three lines (the default
+  // scroll amount is three lines per wheel tick).
+  static const float kScrollbarPixelsPerLine = 100.0f / 3.0f;
   float scroll_delta = wheel_delta / WHEEL_DELTA;
   if (horizontal_scroll) {
     unsigned long scroll_chars = kDefaultScrollCharsPerWheelDelta;
     SystemParametersInfo(SPI_GETWHEELSCROLLCHARS, 0, &scroll_chars, 0);
-    scroll_delta *= static_cast<float>(scroll_chars);
+    // TODO(pkasting): Should probably have a different multiplier
+    // kScrollbarPixelsPerChar here.
+    scroll_delta *= static_cast<float>(scroll_chars) * kScrollbarPixelsPerLine;
   } else {
     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);
+    if (!scroll_by_page) {
+      scroll_delta *=
+          static_cast<float>(scroll_lines) * kScrollbarPixelsPerLine;
+    }
   }
 
   // Set scroll amount based on above calculations.
   if (horizontal_scroll) {
-    // Scrolling up should move left, scrolling down should move right.  This is
-    // opposite Safari, but seems more consistent with vertical scrolling.
     delta_x = scroll_delta;
     delta_y = 0;
   } else {