Thanks for the report. I noticed this too. Very annoying :-(

This is a bug. We should fix it. It’s not really clear how, though.

If the scrolling is occurring because of inertia and the fingers are off of the touchpad, the page shouldn’t zoom once the control key is hit.

An easy way to reproduce this bug is the following:

> Scroll.
> After fingers leaving trackpad, press and hold Control.

The page will zoom drastically. (if you release Control quickly the effect will be less radical.)

I have only started seeing this issue since updating (27.0.1430.0 dev in my case), sadly I'm not sure which version I was using prior to this one, it may have been a while since I restarted Chrome.

Mac OS X 10.6.8

 Issue 181491  has been merged into this issue.

Experiencing the same issue, looks like a regression wait only happens in Canary to me, at least with crtl.

 Issue 227450  has been merged into this issue.

 Issue 228880  has been merged into this issue.

 Issue 229535  has been merged into this issue.

 Issue 229869  has been merged into this issue.

If this is new in M27, I wonder when it started.

I just noticed this after updating to Beta 27 a few days ago.  Very annoying! Especially if it's still zooming from inertia and you press control, as if you were going to change tabs (ctrl+tab). It zooms in or out, depending on the direction you flicked before it started scrolling. 

 Issue 230752  has been merged into this issue.

 Issue 230752  has been merged into this issue.

 Issue 231113  has been merged into this issue.

Ctrl+Scroll is the default shortcut for the system zoom functionality in Mac OS, so Chrome's use of it to zoom web pages is almost a bug in itself. I believe this is disabled by default in 10.8, but previously I believe it was enabled by default. (To enable it go to System Preferences > Accessibility > Zoom > Use scroll gesture with modifier keys to zoom.)

A simple fix therefore in Chrome would be to change the zoom shortcut from Ctrl+Scroll to something else. However this would only really mask the underlying issue which is that inertia from a page scroll is being carried into zooming. I haven't noticed this in any other application so my guess would be that Chromium is handling the inertia itself, and if so, could be controlled easily. If system scroll behaviour is handling this then I guess it's a lot more complicated.

I don't know how the OS and the browser handle key / mouse events, but there seem to be two simple scenarios here which can easily be distinguished.

1. Press and hold Control, then use trackpad or mouse wheel to zoom the page contents.

2. Use trackpad or mouse wheel to scroll the page, and then press Control (+other keys) to trigger some keyboard shortcut.

The difference is the order. The page should only zoom in the first case, when Control is pressed and held BEFORE the scroll event. In the second case, the unwanted page zoom is maddening.

 Issue 226947  &  Issue 231716  look like duplicates of this one.

Also, it appears to be platform independent. (Mac / Linux / Windows)

Manual bisect:- 

Known good build:- 26.0.1410.65 (Official Build 193261) 
Known bad build:-  27.0.1412.0 (Official Build  182397)

Here is bisect window:- 

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog.html?url=%2Ftrunk%2Fsrc&range=181923%3A182110&mode=html

little change:- 
Known good build:- 26.0.1410.65 (Official Build 181864) 

Suspecting culprit is:- 181965

 Issue 225820  has been merged into this issue.

Thanks for the bisect. Yes, looks like 181965 caused this bug.

jam@, could you please take a look at this issue? Thanks in advance.

 Issue 232592  has been merged into this issue.

Just did some investigation. Per one of the above comments, if I start an inertial scroll, then while the page is scrolling I lift off my fingers from the trackpad and press control once, zooming happens.

The odd thing is that the event that comes from RenderWidgetHostViewCOcoa::scrollWheel has the control modifier set. The methods below it are NSwindow, then ChromeEventProcessingWindow, FramedBrowserWindow, NSApplication...). So it looks like the OS is giving a mousewheel event that has control key pressed. I'm not familiar with OS X to say if this is expected behavior or an error, although it seems odd to me.

This got me to thinking how this worked on Mac at all before my change. I was surprised to see that without my change no combination of scroll wheel + meta/option/control changed the zoom level. Do we want this behavior on Mac? If so, what key combination should we use? My patch had used ControlKey on all platforms, which in hindsight should have special cased mac to use meta?

Mac devs: what's your opinion on the above questions? Should this go through UI review? Quickest thing of course is to ifdef my changes to WebContentsImpl (https://codereview.chromium.org/12221144/diff/1/content/browser/web_contents/web_contents_impl.cc) on Mac, but I'm happy to update it based on the above questions.

ctrl-mousewheel does full-screen page zoom if that's enabled in accessibility settings (which it is by default in some OS X versions I think).

I think we never supported page-zoom adjustment by mouseweel + modifier and I don't remember anyone complaining about that, so we should probably just revert to that?

(One can adjust the zoom factor with a pinch gesture on a trackpad, which some people like and some people dislike.)

I see, it makes sense that modifier+scroll doesn't zoom since on Mac there's another way of doing this with gestures. ok I will disable this call for now on Mac.

I may be way off, but I think I recall that we do momentum scroll by simulating scroll events?  Perhaps that is the difference, when the modifier is down and chrome is simulating scroll events for momentum.  If control was pressed before scroll or while fingers are still on trackpad, the OS intercepts with accessibility zoom.  Just a guess.

------------------------------------------------------------------------
r194942 | jam@chromium.org | 2013-04-18T16:37:19.779855Z

Changed paths:
   M http://src.chromium.org/viewvc/chrome/trunk/src/content/browser/web_contents/web_contents_impl.cc?r1=194942&r2=194941&pathrev=194942

Disable page zoom through control+scroll on Mac.

I accidentally enabled this on Mac in r181965. However on Mac this has an unintended consequence of changing the page zoom when the user starts inertial scrolling and presses control right after.

BUG= 178972 

Review URL: https://codereview.chromium.org/14327014
------------------------------------------------------------------------

 Issue 231716  has been merged into this issue.

ty :)

------------------------------------------------------------------------
r194968 | jam@chromium.org | 2013-04-18T18:15:05.990885Z

Changed paths:
   M http://src.chromium.org/viewvc/chrome/branches/1453/src/content/browser/web_contents/web_contents_impl.cc?r1=194968&r2=194967&pathrev=194968

Merge 194942 "Disable page zoom through control+scroll on Mac."

> Disable page zoom through control+scroll on Mac.
> 
> I accidentally enabled this on Mac in r181965. However on Mac this has an unintended consequence of changing the page zoom when the user starts inertial scrolling and presses control right after.
> 
> BUG= 178972 
> 
> Review URL: https://codereview.chromium.org/14327014

TBR=jam@chromium.org

Review URL: https://codereview.chromium.org/14233003
------------------------------------------------------------------------

Hey cool bug fixing dudes, this is also a problem on Linux:  issue 253697 

This is also an issue on Windows: https://code.google.com/p/chromium/issues/detail?id=254612