413989 - Bad lines drawn over background images when zoomed

Status: VERIFIED FIXED

(Core Graveyard :: GFX, defect, P2)

Description

[Dave Townsend [:mossop]]

Attachment: screenshot

At certain levels of zoom I am seeing black lines appearing over the top of content, I think it is repeated background images. See the url and try zooming in or out, you should see the screenshot attached.

The occurs both drawing to a canvas element and to regular page zoom. The effect varies according to the zoom level.

Comment 1

[Dave Townsend [:mossop]]

Regression from the cairo upgrade

Comment 3

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

(In reply to comment #1)
> Regression from the cairo upgrade

Confirmed by dropping to an older version of cairo? By the date range?  Or which?

Comment 4

[Dave Townsend [:mossop]]

Confirmed by comparing builds from the hourly build archive giving the following regression range:

http://bonsai.mozilla.org/cvsquery.cgi?module=PhoenixTinderbox&date=explicit&mindate=1200690960&maxdate=1200692879

Comment 5

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Attachment: scale the source image rect when tiling

roc, does this look like a reasonable thing to do?  The problem is that Quartz seems to always start a tile at integer coordinates, so if we have some scaling going on where the edges of images don't fall on integer coordinates, we get seams.  Here I try to specify a slight scale to the image so that it always completely covers the destination tile space once transformed.  It seems to work fine in my testing.

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Why are you removing all the if (action == DO_IMAGE && op != CAIRO_OPERATOR_OVER) blocks?

This could change the output quite a bit. For example if we're scaling a 2px by 2px image by 0.5001 in each direction using a source transform, instead of getting something that's basically uniform (1px by 1px) we'll get the original image.

I'd be a lot more comfortable if we just checked that the source width and height are non-integers (maybe within epsilon) and if they aren't, take a fallback path.

Comment 7

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Attachment: updated patch

Ok, here's a patch that only does DrawTiledImage if we're within epsilon of integer sizes after transforming.

The other chunks of code that are being removed are bits that I added a while back without thinking straight; they were intended to emulate cairo's "transparent black everywhere outside source bounds" behaviour, but for whatever reason I didn't think that to do that I'd have to explicitly clip out the region that the image was about to get draw into.

Comment 8

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Checked in and upstreamed.

Comment 9

[Rob Campbell [:rc] (:robcee)]

visited a page (http://n3wb.com/forum), scaled up and down with no lines.

Comment 10

[Rob Campbell [:rc] (:robcee)]

Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9b3pre) Gecko/2008012804 Minefield/3.0b3pre ID:2008012804