Make Mac pinch thresholding apply only to zoom (Chromium side)

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 22707f03bb721077c3e1e9261eaefbff4b6743a0..30aaf1c45c601a2d03c031692f34f65483dad9ac 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -1756,7 +1756,8 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
     canBeKeyView_ = YES;
     opaque_ = YES;
     focusedPluginIdentifier_ = -1;
-    lastUsedPinchEventTimestamp_ = 0;
+    pinchLastGestureTimestamp_ = 0;
+    pinchHasReachedZoomThreshold_ = false;
 
     // OpenGL support:
     if ([self respondsToSelector:
@@ -2288,7 +2289,15 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   [responderDelegate_ beginGestureWithEvent:event];
   gestureBeginEvent_.reset(
       new WebGestureEvent(WebInputEventFactory::gestureEvent(event, self)));
-  unusedPinchAmount_ = 0;
+
+  // If more than 1 second has passed since the last pinch gesture ended, reset

[aelias_OOO_until_Jul13, 2015/05/06 23:20:24]

I don't like timeouts as a rule.  Why not reset the threshold immediately on
pinchEnd?

[ccameron, 2015/05/07 17:09:05]

If someone is doing several pinches in a row, to zoom to the maximum (or a
higher) level, they will re-start the gesture once their fingers are spread too
far apart. It feels really awkward to have each begin/end block re-require
thresholding.

[aelias_OOO_until_Jul13, 2015/05/07 18:16:16]

I see.  How about checking if page_scale_factor == minimum_scale from the
CompositorFrameMetadata instead of using the timeout?  It seems like you want to
threshold when not currently zoomed in, but if you're already zoomed in then you
want it to be easier to pinch.

+  // the zoom threshold levels.
+  const NSTimeInterval kSecondsUntilZoomThresholdReEnabled = 1;
+  if ([event timestamp] - pinchLastGestureTimestamp_ >
+      kSecondsUntilZoomThresholdReEnabled) {
+    pinchHasReachedZoomThreshold_ = false;
+    pinchUnusedAmount_ = 0;
+  }
 }
 
 - (void)endGestureWithEvent:(NSEvent*)event {
@@ -2303,7 +2312,8 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
     endEvent.type = WebInputEvent::GesturePinchEnd;
     renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(endEvent);
     gestureBeginPinchSent_ = NO;
-    lastUsedPinchEventTimestamp_ = [event timestamp];
+    if (pinchHasReachedZoomThreshold_)
+      pinchLastGestureTimestamp_ = [event timestamp];
   }
 }
 
@@ -2416,22 +2426,14 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   if (!gestureBeginEvent_)
     return;
 
+  if (!pinchHasReachedZoomThreshold_) {
+      pinchUnusedAmount_ += [event magnification];

[aelias_OOO_until_Jul13, 2015/05/06 23:20:24]

Please make this multiplicative.  Otherwise this will behave differently
depending on the speed of the gesture and how exactly it was divided into
events.  Making it multiplicative will consistently threshold at the same
overall magnitude.

[ccameron, 2015/05/07 17:09:06]

Done. I had made it additive to match the earlier thresholding math.
Empirically, the 40% additive matches a 50% multiplicative.

+      if (pinchUnusedAmount_ < -0.4 || pinchUnusedAmount_ > 0.4)
+          pinchHasReachedZoomThreshold_ = true;
+  }
+
   // Send a GesturePinchBegin event if none has been sent yet.
   if (!gestureBeginPinchSent_) {
-    // If less than 1 second has passed since an intentional pinch zoom
-    // was done, don't threshold zooms, because subsequent zooms are likely
-    // intentional.
-    const NSTimeInterval kSecondsUntilZoomThresholdReEnabled = 1;
-    if ([event timestamp] - lastUsedPinchEventTimestamp_ >
-        kSecondsUntilZoomThresholdReEnabled) {
-      // Require that a 40% zoom be hit before actually zooming the page,
-      // to avoid accidental zooms.
-      // http://crbug.com/478981
-      unusedPinchAmount_ += [event magnification];
-      if (unusedPinchAmount_ > -0.4 && unusedPinchAmount_ < 0.4)
-        return;
-    }
-
     WebGestureEvent beginEvent(*gestureBeginEvent_);
     beginEvent.type = WebInputEvent::GesturePinchBegin;
     renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(beginEvent);
@@ -2439,8 +2441,9 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   }
 
   // Send a GesturePinchUpdate event.
-  const WebGestureEvent& updateEvent =
+  WebGestureEvent updateEvent =
       WebInputEventFactory::gestureEvent(event, self);
+  updateEvent.data.pinchUpdate.zoomDisabled = !pinchHasReachedZoomThreshold_;
   renderWidgetHostView_->render_widget_host_->ForwardGestureEvent(updateEvent);
 }