Closed Bug 799644 Opened 12 years ago Closed 12 years ago

Graphical corruption with opacity and canvas in Maps app


(Core :: Graphics: Layers, defect)

Gonk (Firefox OS)
Not set



blocking-basecamp +
Tracking Status
firefox18 --- fixed
firefox19 --- fixed


(Reporter: cjones, Assigned: cjones)




(1 file)

 (1) Open Maps app
 (2) Press "Layers" button
 (3) Dismiss layers popover

This causes artifacts in the thebes-layer content that's overlayed on the canvas.  See below.

I think this is a grotty enough artifact that it should block, but a workaround in the Maps app is certainly on the table.  Would prefer a platform fix though.
I suspect that this isn't an invalidation problem per se, but more likely either (i) marking ThebesLayers as opaque when they shouldn't be, or (ii) a bug in front->back buffer copy.

Possibly related to bug 796831.

Kan-Ru, do you have cycles to investigate?
See Also: → 796831
Summary: Under-invalidation with opacity and canvas in Maps app → Graphical corruption with opacity and canvas in Maps app
I can only sporadically reproduce on desktop using the steps from comment 0.  It's also intermittent on device, but much easier to reproduce.  However, I found a better way

 (1) Press the "grid" button in the top-right of the UI to pop up the "Welcome!" menu
 (2) Tap anywhere to dismiss it
 (3) GOTO step (1)

With each press, you'll see the faded-out background get darker and darker.  The UI supposed to look something like this

but if you tap enough times, you can make it look like this

Definitely something to do with not clearing or preserving opacity in an RGBA buffer.
The relevant shadow-layer subtree is

1865447232[1420850]:           OGLShadowContainerLayer (0x2d34678) [shadow-transform=[ 1 0; 0 1; 0 20; ]] [shadow-visible=< (x=0, y=0, w=320, h=460); >] [visible=< (x=0, y=0, w=320, h=460); >] [opaqueContent] [metrics={ viewport=(x=0.000000, y=0.000000, w=320.000000, h=460.000000) viewportScroll=(x=0.000000, y=0.000000) displayport=(x=0.000000, y=0.000000, w=0.000000, h=0.000000) scrollId=1 }]
1865447232[1420850]:             OGLShadowThebesLayer (0x24ef818) [shadow-visible=< (x=0, y=0, w=320, h=460); >] [visible=< (x=0, y=0, w=320, h=460); >] [opaqueContent] [valid=< (x=0, y=0, w=320, h=460); >]
1865447232[1420850]:             OGLShadowCanvasLayer (0x3b61228) [shadow-clip=(x=0, y=0, w=320, h=460)] [shadow-transform=[ 1 0; 0 1; 0 50; ]] [shadow-visible=< (x=0, y=0, w=320, h=410); >] [clip=(x=0, y=0, w=320, h=460)] [transform=[ 1 0; 0 1; 0 50; ]] [visible=< (x=0, y=0, w=320, h=410); >]
1865447232[1420850]:             OGLShadowThebesLayer (0x355ba88) [shadow-visible=< (x=0, y=0, w=320, h=460); >] [visible=< (x=0, y=0, w=320, h=460); >] [componentAlpha] [valid=< (x=0, y=0, w=320, h=460); >]

^^^ that layer will have an RGBA buffer since componentAlpha is enabled for it.  That's probably where the problem lies.  (We won't enable component alpha on the phone, but that layer should also end up with an RGBA buffer.)
Even simpler STR

 (1) Tap "grid" button in top-right of UI to pop up the "Welcome!" menu
 (2) Tap to dismiss that popup
 (3) Tap "layers" button in bottom-right

After the animation finishes, a "ghost" of the "Welcome!" UI appears above the layers menu.
Definitely a bug with shadow layers --- if I force maps in-process, the artifacts are gone.
For some reason, in the in-process case, the layers here are marked fixedPosition, but not when OOP ...
In the shadow-layers case, we're retaining a ThebesLayer that appears to be responsible for the artifacts across steps (1)-(3).  In the no-shadow-layers case, we're creating a different layer.  Hmm ...
I think I know what's happening here.  Trying to write a patch but there are many distractions and it's a bit subtle.  Will have something up tonight.
Assignee: nobody → jones.chris.g
What I think is happening is
 - we allocate RGBA back buffer b1
 - we paint b1, send to compositor
 - allocate RGBA back buffer b2
 - paint b2, swap for b1
 - ThebesLayerBuffer starts to paint b1, but it isn't sized properly so we Clear() it
 - TLB allocates buffer b3, paints, sends to compositor
 - we get back b2 and start to paint it.  It happens to be the right size and is RGBA.

However, TLB doesn't know that b2 wasn't cleared when b3 was cleared.  So there's old translucent pixels hanging around in the buffer.

I wrote a patch that /should/ have fixed this, but it didn't.  So I'm not sure my guess is right.

Need to add image tracing to analyze further.  Thank heavens I can repro on desktop!
Some very basic image tracing tells me that this bug isn't caused by bugs in front->back copy; it seems to be caused by composite-active-layers-to-inactive layer.  (I don't see my front->back sync tracing get hit, but I think that's a bug in my tracing.)  There are two big relatively recent changes to this logic.  First is bug 788044, but on its earliest parent commit

I see the same bug.  (Amazingly the gaia build actually starts up on that rev!)  The other big change was bug 792663.  However, that work landed after 33087122ace7 so I don't think that's it either, but I'll double check.
The bug is also present on , but manifests itself a bit differently.  So I'm guessing this has been a bug "forever" :(.
It also wasn't bug 773192.  I can reproduce the same bug when forcing Maps in-process and enabling omtc.
Thanks for looking into this Chris... Sorry it hasn't been easier to fix :-)
The answer was literally staring me in the face for 5 hours this afternoon, in the form of about 10 tabs with data:image/png captures, and it took me that long to put 2+2 together.  Need something stronger than /headdesk for this ...
Attachment #672684 - Flags: review?(matt.woodrow)
Attachment #672684 - Flags: review?(matt.woodrow) → review+
Is bug 799606 another dupe - or at least the B2G stuff I noted there?
I figured the fix would be something like this. Sorry I didn't get to bug 793840 sooner.
clee, I would like to request this bug as a P1 crit please; this really needs a fix soon because it affects a lot of apps, and places in gaia/b2g.
Flags: needinfo?(clee)
I've been treating this as P1/critical and dropping other work to fix it.  A patch has already landed.  What more do you want?
Flags: needinfo?(clee)
Closed: 12 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla19
@cjones... oh awesome.... didn't realize it.  Can I get a chocolate hat too?  :)

gaia master : 18107c6961b8c3f559c82fc7be8ba411c4a67c28
mozilla-aurora(hg) : 6735d6d13751
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