Protoype Mac input event filter

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index 86f5a774225371db85fd1cc8dbf5f64a44489c0e..a87576cea28eb693aa4979791e369aa00cb86506 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -75,6 +75,7 @@
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 #include "ui/gfx/geometry/size_conversions.h"
+#include "ui/gfx/geometry/vector2d_f.h"
 #include "ui/gfx/scoped_ns_graphics_context_save_gstate_mac.h"
 #include "ui/gfx/screen.h"
 #include "ui/gl/gl_switches.h"
@@ -391,6 +392,90 @@ blink::WebScreenInfo GetWebScreenInfo(NSView* view) {
 
 namespace content {
 
+class WheelEventRailFilterMac {
+ public:
+  WheelEventRailFilterMac() :
+      mode_(MODE_UNINITIALIZED) {
+  }
+
+  ~WheelEventRailFilterMac() {
+  }
+
+  WebMouseWheelEvent FilterWheelEvent(const WebMouseWheelEvent& event) {
+    // This number came from 0.5 feeling too big and 0.9 feeling too small.
+    const float kDecayConstant = 0.8f;
+    // Require a slightly-more-than-diagonal motion against the current
+    // scroll to break the rails.
+    const float kSinThetaToBreakRails = 0.8f;
+    // Require a consistently-unidirectional motion to reset the rails
+    // after they have been broken.
+    const float kSinThetaToResetRails = 0.02f;
+
+    if (event.phase == blink::WebMouseWheelEvent::PhaseBegan) {
+      mode_ = MODE_UNINITIALIZED;
+      decayed_delta_ = gfx::Vector2dF();
+    }
+    if (event.deltaX == 0 && event.deltaY == 0)
+      return event;
+
+    decayed_delta_.Scale(kDecayConstant);
+    decayed_delta_ += gfx::Vector2dF(fabsf(event.deltaX), fabsf(event.deltaY));
+
+    float sin_theta_horizontal = decayed_delta_.y() / decayed_delta_.Length();
+    float sin_theta_vertical = decayed_delta_.x() / decayed_delta_.Length();
+
+    switch (mode_) {
+      case MODE_UNINITIALIZED:
+        if (decayed_delta_.x() > decayed_delta_.y())
+          mode_ = MODE_HORIZONTAL;
+        else
+          mode_ = MODE_VERTICAL;
+        break;
+      case MODE_HORIZONTAL:
+        if (sin_theta_horizontal > kSinThetaToBreakRails)
+          mode_ = MODE_FREE;
+        break;
+      case MODE_VERTICAL:
+        if (sin_theta_vertical > kSinThetaToBreakRails)
+          mode_ = MODE_FREE;
+        break;
+      case MODE_FREE:
+        if (sin_theta_horizontal < kSinThetaToResetRails)
+          mode_ = MODE_HORIZONTAL;
+        if (sin_theta_vertical < kSinThetaToResetRails)
+          mode_ = MODE_VERTICAL;
+        break;
+    }
+
+    WebMouseWheelEvent result = event;
+    switch (mode_) {
+      case MODE_HORIZONTAL:
+        printf("mode:Horiz\n");
+        result.deltaY = 0;
+        break;
+      case MODE_VERTICAL:
+        printf("mode:Vert\n");
+        result.deltaX = 0;
+        break;
+      default:
+        printf("Free\n");
+        break;
+    }
+    return result;
+  }
+  
+ private:
+  enum Mode {
+    MODE_UNINITIALIZED,
+    MODE_HORIZONTAL,
+    MODE_VERTICAL,
+    MODE_FREE,
+  };
+  Mode mode_;
+  gfx::Vector2dF decayed_delta_;
+  gfx::Vector2dF decayed_delta_other_;
+};
+
 ////////////////////////////////////////////////////////////////////////////////
 // DelegatedFrameHost, public:
 
@@ -525,7 +610,8 @@ void RenderWidgetHostViewBase::GetDefaultScreenInfo(
 
 RenderWidgetHostViewMac::RenderWidgetHostViewMac(RenderWidgetHost* widget,
                                                  bool is_guest_view_hack)
-    : render_widget_host_(RenderWidgetHostImpl::From(widget)),
+    : wheel_event_rail_filter_(new WheelEventRailFilterMac),
+      render_widget_host_(RenderWidgetHostImpl::From(widget)),
       text_input_type_(ui::TEXT_INPUT_TYPE_NONE),
       can_compose_inline_(true),
       browser_compositor_state_(BrowserCompositorDestroyed),
@@ -2257,7 +2343,9 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
     bool canRubberbandRight = true;
     const WebMouseWheelEvent webEvent = WebInputEventFactory::mouseWheelEvent(
         event, self, canRubberbandLeft, canRubberbandRight);
-    renderWidgetHostView_->render_widget_host_->ForwardWheelEvent(webEvent);
+    renderWidgetHostView_->render_widget_host_->ForwardWheelEvent(
+        renderWidgetHostView_->wheel_event_rail_filter_->FilterWheelEvent(
+            webEvent));
   }
 
   if (endWheelMonitor_) {
@@ -2380,7 +2468,9 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
     BOOL canRubberbandRight = [responderDelegate_ canRubberbandRight:self];
     const WebMouseWheelEvent webEvent = WebInputEventFactory::mouseWheelEvent(
         event, self, canRubberbandLeft, canRubberbandRight);
-    renderWidgetHostView_->render_widget_host_->ForwardWheelEvent(webEvent);
+    renderWidgetHostView_->render_widget_host_->ForwardWheelEvent(
+        renderWidgetHostView_->wheel_event_rail_filter_->FilterWheelEvent(
+            webEvent));
   }
 }