351105 - Smooth scrolling on two-finger trackpad regardless of preference

Status: RESOLVED FIXED

(Firefox :: Shell Integration, defect)

Description

[Allan]

User-Agent:       Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-GB; rv:1.8.1b2) Gecko/20060821 Firefox/2.0b2
Build Identifier: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-GB; rv:1.8.1b2) Gecko/20060821 Firefox/2.0b2

When using two-finger trackpad scrolling on a MacBook, Firefox scrolls smoothly regardless of the preference setting. (This is bad because the cheap MacBook screen has bad color ghosting on scroll, and FF was the only browser that didn't show it)

Reproducible: Always

Steps to Reproduce:
1. Go to a page with lots of color text
2. Turn off smooth scrolling in FF preferences
3. Two-finger trackpad scroll

Actual Results:  
The document scrolls smoothly

Expected Results:  
The document should have scrolled in discrete small amounts.

Comment 1

[Adam Guthrie]

I think this might be intentional, but I'm not sure. Mark will know since he implemented it. :)

Comment 2

[Mark Mentovai]

You're experiencing pixel-scrolling, which is different (and better) than smooth scrolling.  Pixel scrolling lets certain mouse devices, like two-finger touchpads and Mighty Mice, tell us how much to scroll in pixels instead of lines.  Smooth scrolling lets mice convey scroll information as the traditional number of lines to scroll, but animates the transition.

Pixel scrolling was initially added in bug 319078.  No provisions were made for bypassing the behavior.  If your hardware (touchpad or Mighty Mouse) and driver (present in 10.4 and later) support it, you'd get pixel scrolling.  I hadn't considered that the effect might be undesirable on exceptionally slow-to-refresh displays, and in fact, yours is the first negative feedback I've seen about the implementation.  (I think MacBook Pros are more popular in my circle than MacBooks.)

Fortunately for you and MacBook-toting users everywhere, we had to disable pixel scrolling in bug 347626 because it caused some evil behaviors in some web applications and in lists and trees displayed by Mozilla.  If you pick up a current nightly, or wait for 2.0rc1, you'll find the old notchy scrolling behavior restored, even with the two-finger touchpad.

If we ever wind up turning pixel scrolling back on (bug 350471), maybe we should add a (hidden) pref to control it, to account for lazy liquid crystals.  I'm making that bug dependent on this report so that we'll remember this in the future, but closing this one as works-for-me because pixel scrolling is already off everywhere, and you can pick up a fresh nightly build to verify.

Comment 3

[Markus Stange [:mstange]]

In bug 350471 I added a preference, "mousewheel.enable_pixel_scrolling".