612695 - Drawing is halted during heavy call loads from mousemove.

Status: UNCONFIRMED

(Core :: Graphics: Canvas2D, defect)

Description

[Adam]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.8) Gecko/20100729 Iceweasel/3.6.7 (like Firefox/3.6.7)
Build Identifier: Mozilla/5.0 (X11; Linux i686; rv:2.0b8pre) Gecko/20101112 Firefox/4.0b8pre

When calling to draw on the canvas from mousemove events, and if the drawing is sufficiently complex/slow, the canvas is never updated so long as the mouse keeps moving quickly.  

Reproducible: Always

Steps to Reproduce:
1. Load included test.html
2. mousedown on canvas
3. move the mouse slowly (~10px/sec)
4. continuously move the mouse rapidly (~100px/sec)

Actual Results:  
The canvas is never updated during rapid mouse movement.

Expected Results:  
The canvas to be updated, even if it lags in doing so, as in Fx 3.6.

I am not entirely clear whether this bug rests with changes to the canvas component or with changes the JavaScript engine, but profiling the code (with Firebug's time()/timeEnd(); these are left in the test, but commented out) indicates that the JavaScript execution time is unaffected by the workaround, so canvas seemed more likely.  

I have included a checkbox in the test to turn on the workaround so that the two can be compared, but I feel the code without setTimeout is a regression from Fx 3.6 where the calls would be delayed, but the canvas still updated.  Chromium also acts as 3.6 does.  Other browsers were not tested.

Comment 1

[Adam]

Attachment: testcase to demonstrate the behavior

Comment 2

[Boris Zbarsky [:bzbarsky]]

I don't see a problem here on Mac....  Linux-only?

Comment 3

[Adam]

Correction to the earlier information:

Fx3.6.9 official: present
Iceweasel 3.6: not present
Fx4b8pre+ official: present
Fx4b10pre local build: not present

I was also able to test on Mac OS X with Firefox 3.6.12 and 4b9 and did not experience it there.

It's likely this is a bug with one or more of the static libraries needed for canvas on Linux that are used for official builds, as both Iceweasel and my local build use system libraries.

Comment 4

[Boris Zbarsky [:bzbarsky]]

If you build with non-system cairo, does your local build show the issue?