707610 - Striped background flickers and tears when scrolling

Status: RESOLVED DUPLICATE of bug 555834

(Core :: Graphics, defect)

Description

[Justin Dolske [:Dolske]]

Certain background patterns can exhibit strange patterns on monitors. CRTs were infamous for Moiré patterns, and I've noticed related effects with horizontally-striped backgrounds on LCDs.

http://coe.berkeley.edu/engnews/fall02/3S/polarbear.html has an example of one of these backgrounds, it's alternating 1px lines of blue and gray. When scrolling on my MBP, the background seems to change to a bluer, more solid color. This happens on Firefox Nightly, Chrome, and Safari.

But here's the interesting difference: Only in Firefox does the background seem to tear while scrolling (ie, both pattern and solid effect visible, changing over at random points on the screen). In Chrome and Safari, there is no tearing although there is a uniform pattern/solid flickering.

While perhaps a bit of an edge-case test, I've also noticed that scrolling seems more readable in Chrome/Safari compared to Firefox -- they're all moving fairly smoothly and without jank, but text in Firefox seems to blur a bit instead of remaining sharp. I wonder if it's the same cause as this tearing?

Comment 1

[Markus Stange [:mstange]]

Both symptoms are caused by the lack of vsync (bug 555834). If you want to see what it would look like in Firefox if we activated vsync, start Quartz Debug, set Beam Sync to Force and make sure that the Quartz Debug window overlaps the Firefox window.