482931 - With Acceleration in X disabled, scrolling using mouse wheel is very slow. Dragging scrollbar is ok

Status: RESOLVED INCOMPLETE

(Firefox :: General, defect)

Description

[Alain Knaff]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.7) Gecko/2009030503 Fedora/3.0.7-1.fc10 Firefox/3.0.7
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.7) Gecko/2009030503 Fedora/3.0.7-1.fc10 Firefox/3.0.7

Due to a buggy Intel i810 chipset on my computer, I had to switch off Acceleration in X (Option "Accel"   "Off" in /etc/X11/xorg.conf). This resolved the display problems that I had on that buggy chipset, but has the unfortunate side effect of making mouse wheel scrolling in Firefox excessively slow.
You may think that this is expected after switching off acceleration, but:
1. It only affects Firefox and only happens when using the mousewheel.
2. Scrolling by dragging the scrollbar has adequate speed.
3. Scrolling in other applications (such as konqueror, or even thunderbird!) is acceptably fast, even when using the mouse wheel.

The weirdest thing is that the page continues scrolling for a while, even after I stopped manipulating the mouse wheel. It really looks as if Firefox was trying to do some cute (but GPU intensive) animation while scrolling (such as showing each intermediary position of scroll), and doesn't notice that the GPU doesn't follow. Other apps apparently scroll directly to the target position when they notice that the graphics engine doesn't follow. And even Firefox apparently does that when using the scrollbar rather than the wheel.

Or is this because dragging the scrollbar directly gives Firefox the requested _position_ whereas the mousewheel only sends deltas? But it can't be exactly hard to have an internal counter that integrates these deltas (without trying to display the page at each step, if engine is too slow)

Addressing this issue will not only help people with broken hardware, but also people using older computers, which might not have any graphics acceleration to begin with.

Reproducible: Always

Steps to Reproduce:
1. Disable X acceleration in /etc/X11/xorg.conf by inserting the following line into the "Device" section:
    Option "Accel"   "Off"
2. Restart X
3. Go to any page long enough to need scrolling (such as this one here: https://bugzilla.mozilla.org/enter_bug.cgi?product=Firefox&format=guided)
4. Scroll using the mouse wheel.
5. Stop scrolling

Actual Results:  
It very slowly starts scrolling, showing each intermediary scrolled position. Scrolling continues even after stopping to manipulate the mouse wheel.

Expected Results:  
If Firefox notices that the GPU doesn't follow with scrolling, it should skip intermediary frames, and directly scroll to the final target.

Or at least, this should be a config option, if such optimization bothers users on fast displays.

Comment 1

[Wayne Mery (:wsmwk)]

Alain, do you still see this problem?

Comment 2

[Alain Knaff]

It is still an issue, but not on all sites.

On Slashdot's comment pages, for instance, the problem still stays pretty noticable.

Comment 3

[Tyler Downer [He/Him]]

Reporter, are you still seeing this issue with Firefox 3.6.10 or later in safe mode? If not, please close. These links can help you in your testing.
http://support.mozilla.com/kb/Safe+Mode
http://support.mozilla.com/kb/Managing+profiles

Comment 4

[Alain Knaff]

It is still an issue, even in 3.6.10 in safe mode.

Comment 5

[Wayne Mery (:wsmwk)]

thanks for the update. odd that no one else is cc.
do you also see in firefox 4?

Comment 6

[Wayne Mery (:wsmwk)]

(In reply to Wayne Mery (:wsmwk) from comment #5)
> thanks for the update. odd that no one else is cc.
> do you also see in firefox 4?

Comment 7

[Phoenix]

Resolved per whiteboard