mac: Only let two-finger-scrolling trigger history if web doesn't swallow gesture

chrome/browser/renderer_host/render_widget_host_view_mac.mm

Index: chrome/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/chrome/browser/renderer_host/render_widget_host_view_mac.mm b/chrome/browser/renderer_host/render_widget_host_view_mac.mm
index badd17fd62903c1344f9bf37e044bb381ca78ff9..d9bd8a81a8bbbd79875385002f864a040c8d8fa1 100644
--- a/chrome/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/chrome/browser/renderer_host/render_widget_host_view_mac.mm
@@ -2,9 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "chrome/browser/renderer_host/render_widget_host_view_mac.h"
+
 #include <QuartzCore/QuartzCore.h>
 
-#include "chrome/browser/renderer_host/render_widget_host_view_mac.h"
+#include <cmath>
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ -17,9 +19,12 @@
 #include "base/sys_info.h"
 #include "base/sys_string_conversions.h"
 #include "chrome/browser/browser_trial.h"
+#include "chrome/browser/mac/closure_blocks_leopard_compat.h"
 #import "chrome/browser/renderer_host/accelerated_plugin_view_mac.h"
 #import "chrome/browser/renderer_host/text_input_client_mac.h"
 #include "chrome/browser/spellchecker/spellchecker_platform_engine.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_list.h"
 #import "chrome/browser/ui/cocoa/rwhvm_editcommand_helper.h"
 #import "chrome/browser/ui/cocoa/view_id_util.h"
 #include "chrome/common/render_messages.h"
@@ -56,6 +61,44 @@ using WebKit::WebMouseEvent;
 using WebKit::WebMouseWheelEvent;
 using WebKit::WebGestureEvent;
 
+// Forward-declare symbols that are part of the 10.7 SDK.

[Mark Mentovai, 2011/08/15 16:55:36]

These are just declarations. Not too much about them is specifically “forward.”

(Did you swipe the comment from somewhere? I just mentioned the same nit on a
recent Avi change.)

[Nico, 2011/08/15 17:05:30]

Removed "Forward-".
Yes, that was from browser_window_controller.mm where I deleted the comment.

+#if !defined(MAC_OS_X_VERSION_10_7) || \
+    MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7
+
+enum {
+    NSEventPhaseNone        = 0, // event not associated with a phase.
+    NSEventPhaseBegan       = 0x1 << 0,
+    NSEventPhaseStationary  = 0x1 << 1,
+    NSEventPhaseChanged     = 0x1 << 2,
+    NSEventPhaseEnded       = 0x1 << 3,
+    NSEventPhaseCancelled   = 0x1 << 4,
+};
+typedef NSUInteger NSEventPhase;
+
+enum {
+     NSEventSwipeTrackingLockDirection = 0x1 << 0,
+     NSEventSwipeTrackingClampGestureAmount = 0x1 << 1
+};
+typedef NSUInteger NSEventSwipeTrackingOptions;
+
+
+@interface NSEvent (LionAPI)
++ (BOOL)isSwipeTrackingFromScrollEventsEnabled;
+
+- (NSEventPhase)phase;
+- (CGFloat)scrollingDeltaX;
+- (CGFloat)scrollingDeltaY;
+- (void)trackSwipeEventWithOptions:(NSEventSwipeTrackingOptions)options
+          dampenAmountThresholdMin:(CGFloat)minDampenThreshold
+                               max:(CGFloat)maxDampenThreshold
+                      usingHandler:(void (^)(CGFloat gestureAmount,
+                                             NSEventPhase phase,
+                                             BOOL isComplete,
+                                             BOOL *stop))trackingHandler;
+@end
+
+#endif  // 10.7
+
 static inline int ToWebKitModifiers(NSUInteger flags) {
   int modifiers = 0;
   if (flags & NSControlKeyMask) modifiers |= WebInputEvent::ControlKey;
@@ -1018,6 +1061,22 @@ void RenderWidgetHostViewMac::SetVisuallyDeemphasized(const SkColor* color,
   // This is not used on mac.
 }
 
+void RenderWidgetHostViewMac::UnhandledWheelEvent(
+    const WebKit::WebMouseWheelEvent& event) {
+  [cocoa_view_ setGotUnhandledWheelEvent:YES];
+}
+
+void RenderWidgetHostViewMac::SetHasHorizontalScrollbar(
+    bool has_horizontal_scrollbar) {
+  [cocoa_view_ setHasHorizontalScrollbar:has_horizontal_scrollbar];
+}
+
+void RenderWidgetHostViewMac::SetScrollOffsetPinning(
+    bool is_pinned_to_left, bool is_pinned_to_right) {
+  [cocoa_view_ setPinnedLeft:is_pinned_to_left];
+  [cocoa_view_ setPinnedRight:is_pinned_to_right];
+}
+
 void RenderWidgetHostViewMac::ShutdownHost() {
   shutdown_factory_.RevokeAll();
   render_widget_host_->Shutdown();
@@ -1101,6 +1160,10 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
 
 @synthesize selectedRange = selectedRange_;
 @synthesize markedRange = markedRange_;
+@synthesize gotUnhandledWheelEvent = gotUnhandledWheelEvent_;
+@synthesize isPinnedLeft = isPinnedLeft_;
+@synthesize isPinnedRight = isPinnedRight_;
+@synthesize hasHorizontalScrollbar = hasHorizontalScrollbar_;
 
 - (id)initWithRenderWidgetHostViewMac:(RenderWidgetHostViewMac*)r {
   self = [super initWithFrame:NSZeroRect];
@@ -1231,10 +1294,6 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
     WebGestureEvent webEvent = WebInputEventFactory::gestureEvent(event, self);
     renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(webEvent);
   }
-
-  // Forward the gesture event to the next responder so that the browser window
-  // controller has a chance to act on back/forward gestures.
-  [[self nextResponder] beginGestureWithEvent:event];

[Mark Mentovai, 2011/08/15 16:55:36]

Nice subtraction. Thanks to Alexei for catching it.

 }
 
 - (void)endGestureWithEvent:(NSEvent*)event {
@@ -1244,10 +1303,6 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
     WebGestureEvent webEvent = WebInputEventFactory::gestureEvent(event, self);
     renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(webEvent);
   }
-
-  // Forward the gesture event to the next responder so that the browser window
-  // controller has a chance to act on back/forward gestures.
-  [[self nextResponder] endGestureWithEvent:event];
 }
 
 - (BOOL)performKeyEquivalent:(NSEvent*)theEvent {
@@ -1497,9 +1552,80 @@ void RenderWidgetHostViewMac::SetTextInputActive(bool active) {
     [NSCursor setHiddenUntilMouseMoves:YES];
 }
 
-- (void)scrollWheel:(NSEvent *)theEvent {
+- (BOOL)maybeHandleHistorySwiping:(NSEvent*)theEvent {

[Mark Mentovai, 2011/08/15 16:55:36]

Since you don’t declare this in an @interface, you should stick a
one-or-two-line comment above it just letting readers know what it does and what
it returns.

[Nico, 2011/08/15 17:05:30]

Done.

+  BOOL canUseLionApis = [theEvent respondsToSelector:@selector(phase)];
+  if (!canUseLionApis)
+    return NO;
+
+  // Scroll events always go to the web first, and can only trigger history
+  // swiping if they come back unhandled.
+  if ([theEvent phase] == NSEventPhaseBegan) {
+    totalScrollDelta_ = NSZeroSize;
+    gotUnhandledWheelEvent_ = false;
+  }
+
+  if (gotUnhandledWheelEvent_ &&
+      [NSEvent isSwipeTrackingFromScrollEventsEnabled] &&
+      [theEvent phase] == NSEventPhaseChanged) {
+    totalScrollDelta_.width += [theEvent scrollingDeltaX];
+    totalScrollDelta_.height += [theEvent scrollingDeltaY];
+
+    bool isHorizontalGesture =
+      std::abs(totalScrollDelta_.width) > std::abs(totalScrollDelta_.height);

[Mark Mentovai, 2011/08/15 16:55:36]

Are the |abs| calls helpful here at all? Can’t we do the inequality in the
floating-point domain? (Drop the <cmath> #include if so.)

[Nico, 2011/08/15 17:05:30]

Yes, width and height can be both positive or negative depending on the
direction of the swipe. We care only about "is this more horizontal than
vertical", not the sign, so abs is what we want. (If I understood the question
correctly.)

[Mark Mentovai, 2011/08/15 17:58:24]

Nico wrote:
My question was bogus anyway. Need more 0xc0ffee.

+
+    bool isRightScroll = [theEvent scrollingDeltaX] < 0;
+    bool goForward = isRightScroll;
+
+    if (isHorizontalGesture &&
+        // If "forward" is inactive and the user rubber-bands to the right,
+        // "isPinnedLeft" will be false.  When the user then rubber-bands to
+        // the left in the same gesture, that should trigger history
+        // immediately if there's no scrollbar, hence the check for
+        // hasHorizontalScrollbar_.
+        (!hasHorizontalScrollbar_ ||
+        // One would think we have to check canGoBack / canGoForward here, but
+        // that's actually done in the renderer
+        // (ChromeClientImpl::shouldRubberBand()), when it decides if it should
+        // rubberband or send back an event unhandled.
+            (isPinnedLeft_ && !isRightScroll) ||
+            (isPinnedRight_ && isRightScroll))) {
+      // The way this api works: gestureAmount is between -1 and 1 (float). If
+      // the user does the gesture for more than about 25% (i.e. < -0.25 or >
+      // 0.25) and then lets go, it is accepted, we get a NSEventPhaseEnded,
+      // and after that the block is called with amounts animating towards 1
+      // (or -1, depending on the direction).  If the user lets go below that
+      // threshold, we get NSEventPhaseCancelled, and the amount animates
+      // toward 0.
+      [theEvent trackSwipeEventWithOptions:0
+                  dampenAmountThresholdMin:-1
+                                       max:1
+                              usingHandler:^(CGFloat gestureAmount,
+                                             NSEventPhase phase,
+                                             BOOL isComplete,
+                                             BOOL *stop) {
+          // |gestureAmount| obeys -[NSEvent isDirectionInvertedFromDevice]
+          // automatically.
+          // TODO(thakis): UI.
+          Browser* browser = BrowserList::GetLastActive();
+          if (phase == NSEventPhaseEnded && browser) {
+            if (goForward)
+              browser->GoForward(CURRENT_TAB);
+            else
+              browser->GoBack(CURRENT_TAB);
+          }
+        }];
+      return YES;
+    }
+  }
+  return NO;
+}
+
+- (void)scrollWheel:(NSEvent*)theEvent {
   [self cancelChildPopups];
 
+  if ([self maybeHandleHistorySwiping:theEvent])
+    return;
+
   const WebMouseWheelEvent& event =
       WebInputEventFactory::mouseWheelEvent(theEvent, self);
   if (renderWidgetHostView_->render_widget_host_)