Bug 53796 – [Qt] Fixed background does not work with Tiled Backing Store

• Status: RESOLVED
• Resolution: INVALID
• Component: Layout and Rendering

[Roger Scott]

STEPS TO REPRODUCE:
1.Start QtTestBrowser
2. Load http://iop1.nokia-boston.com/CSS/index.html
3. Select CSS3_MultipleBackgroundImages link.
4. Click on "24.Background Attachment Property with value as Fixed." link.
5. Select Develop->QGrapicsView->Toggle use of QGrapicsView
6. Select Develop->QGrapicsView->Toggle use of Tiled Backing Store
7.. Scroll down the page. (may have to refresh first)

ACTUAL RESULTS:
Background image is scrolled along with the content.

EXPECTED RESULTS:
Background image should not scroll, only content should scroll.

[Roger Scott]

From several comments I have read, it seems likely that Fixed Backgrounds are incompatible with use of Tiled Backing store.

I am working on a patch where I check style and disable use of TiledBackingStore for frames that have Fixed Background in Qt wekkit/api code. This worked in preliminary testing.

Please assign me to this error....thanks.

[Benjamin Poulain]

Is that on Symbian? Because I remember disabling fixed background on embedded for performance.

(In reply to comment #1)
> I am working on a patch where I check style and disable use of TiledBackingStore for frames that have Fixed Background in Qt wekkit/api code. This worked in preliminary testing.

Could you upload what you already have? I am a bit afraid of this approach.

I also do not understand why you would use tiling if you are not using resize to content. I set a low priority for now because of that.

[Noam Rosenthal]

Can we close this bug? It's seem stale.

[Allan Sandfeld Jensen]

The bug is probably still true to a point, but I think it is being solved in a different bug, and the test case here is dead.

[Allan Sandfeld Jensen]

Fixed background still doesn't work in WebKit trunk. We could disable them for tiled backing-store like we do when delegated-scroll is set.

[Antonio Gomes]

(In reply to comment #5)
> Fixed background still doesn't work in WebKit trunk. We could disable them for tiled backing-store like we do when delegated-scroll is set.

Have you tried enabling FAST_MOBILE_SCROLLING ?

[Allan Sandfeld Jensen]

(In reply to comment #6)
> (In reply to comment #5)
> > Fixed background still doesn't work in WebKit trunk. We could disable them for tiled backing-store like we do when delegated-scroll is set.
> 
> Have you tried enabling FAST_MOBILE_SCROLLING ?

That was my point. Qt has always FAST_MOBILE_SCROLLING set, but only uses it when delegated scrolling is set, we could perhaps also use it when tiled backing store is set.

[Allan Sandfeld Jensen]

Created attachment 179700 [details]
Patch

[Jocelyn Turcotte]

Comment on attachment 179700 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=179700&action=review

> Source/WebCore/rendering/RenderObject.cpp:1913
> -        if (view()->frameView()->delegatesScrolling())
> +        if (view()->frameView()->delegatesScrolling() || view()->frameView()->paintsEntireContents())

I think we could replace delegatesScrolling by paintsEntireContents instead of OR-ing it, they seem to always be enabled together.
This hack is more related to painting than scrolling anyway.

> Source/WebKit/qt/WebCoreSupport/FrameLoaderClientQt.cpp:291
> -
> -        m_frame->view()->setPaintsEntireContents(resizesToContents);
> +        bool paintsEntireContents = resizesToContents || m_webFrame->pageAdapter->settings->testAttribute(QWebSettings::TiledBackingStoreEnabled);
> +        m_frame->view()->setPaintsEntireContents(paintsEntireContents);

This is nasty since this forces parts of the resizesToContents behavior if QWebSettings::TiledBackingStoreEnabled is set without QGraphicsWebView::resizesToContents reflecting it. Like stated in comment #2, I see no advantage of using TiledBackingStoreEnabled without resizesToContents, so perhaps we should just work around the API design defect by making TiledBackingStoreEnabled conditional to resizesToContents, or to automatically enable the later if the former is set.

[Jocelyn Turcotte]

=== Bulk closing of Qt bugs ===

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