1518840 - Missing text-shadow when a lot of text has the property

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P3)

Description

[Nicolas Silva [:nical]]

Go to any page with a lot of text (for example https://www.w3.org/TR/html52/single-page.html) and add the property text-shadow: black 0px 0px 10px; such that it applies to a lot of text. Then scroll around, you should see some text missing the shadow, when scrolling away and back it's not necessarily the same text that misses its shadows.

Comment 1

[Matt Woodrow (:mattwoodrow)]

Getting rid of the blur on the text-shadow stops this from reproducing. Is there a limit to how many blur filters we will draw in a given frame?

Comment 2

[Matt Woodrow (:mattwoodrow)]

Each blurred shadow seems to also create a picture, so maybe the limit is on those?

Any ideas Glenn?

Comment 3

[Nicolas Silva [:nical]]

Attachment: test case

Comment 4

[Glenn Watson [:gw]]

There's no specific limit on pictures and / or blur filters. This will require more detailed investigation to see what is happening.

Comment 5

[u480271]

Attachment: Bug 1518840 - Allow cloning of BuiltDisplayListIter to allow effective peeking.

Current implementation of peek() on iterator destroys the current item. Since
iterator has immutable share of the underlying data stream, cloning of iterator
allows `forking` of an iterator to peek at the next item with out losing access
to the current item.

Comment 6

[u480271]

Attachment: Bug 1518840 - Collapse compatible PopAllShadows/PushShadow runs.

Motivated by pattern of PushShadow/Text/PopAllShadows/PushShadow/... when
processing blocks of text, skip PopAllShadows/PushShadow pair if the PushShadow
contains a shadow compatible, ie. shadows that have the same attributes offset,
blur, color, etc, with the current open shadow.

Depends on D16434

Comment 7

[u480271]

:mattwoodrow points out my patches might just hide the missing shadows because the collapse renders fewer shadows. I'll investigate the before patch situation.

Comment 8

[u480271]

Attachment: renderdoc.png

Comment 9

[u480271]

I've investigated what is happening to the missing text-shadows and I can see that they are being rendered but the texture cache entry for the shadow is empty (ie. all alpha is 0). I captured the rendering in RenderDoc and looked at the texture 2d array to confirm this. (see renderdoc attachment)

I've checked the submission of the picture primitives and the texture cache appears to report that the entries are valid.

Also, if you keep scrolling down slowly, no new shadows are added after some point.

Comment 10

[u480271]

Working with :emilio and :gw on the issue of double rendering of blurs it was hit on that instead of using the texture cache that using picture caching might be a better solution. Switching from texture cache to picture cache fixes the issue of missing shadows.

Comment 11

[u480271]

Attachment: Bug 1518840 - P1: Remove rendering blurs into texture cache.

Caching text-shadows into texture cache was leading to rendering artifacts with
missing shadows. Switch to using the picture path for all picture blurs and
rely upon picture caching to reduce repetitive work.

Comment 12

[u480271]

I notice that with picture caching that we don't get batching of the initial text runs like we did when using texture cache. I'm opening a follow up bug to investigate that.

Comment 13

[u480271]

Attachment: Bug 1518840 - P2: Clean up dead code warnings.

Depends on D17329

Comment 15

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/48cff9538a5e
P1: Remove rendering blurs into texture cache. r=gw,emilio
https://hg.mozilla.org/integration/autoland/rev/fdb28a194129
P2: Clean up dead code warnings. r=gw

Comment 16

[Andrei Ciure[:aciure]]

https://hg.mozilla.org/mozilla-central/rev/48cff9538a5e
https://hg.mozilla.org/mozilla-central/rev/fdb28a194129