[Interest] Tearing in Quick2 flickable-based items with clipping enabled

[Ola Røer Thorsen]

Hi Gunnar, I'll see if I can create a small example that reproduces it.

Cheers,
Ola



2013/11/13 Sletta Gunnar <Gunnar.Sletta at digia.com>

>  If this consistently reproducible across desktop and device, then I
> would appreciate a bugreport with an example that reproduces it. It is not
> a known issue to me at least. (bugreports.qt-project.org)
>
>  Clipping is implemented using scissor or stencil depending on the
> complexity of the mask, no intermediate texture is involved.
>
>  cheers,
> Gunnar
>
>  ------------------------------
> *Fra:* interest-bounces+gunnar.sletta=digia.com at qt-project.org[interest-bounces+gunnar.sletta=
> digia.com at qt-project.org] på vegne av Ola Røer Thorsen [ola at silentwings.no
> ]
> *Sendt:* 13. november 2013 15:29
> *To:* interest at qt-project.org
> *Emne:* [Interest] Tearing in Quick2 flickable-based items with clipping
> enabled
>
>   Hi all,
>
>  I'm seeing tearing-effects when scrolling in ListView and other items
> based on Flickable when clipping is enabled. This is running on both a
> Linux desktop as well as an embedded Linux device (eglfs). The Qt version
> is 5.1.1.
>
>  The systems are running with vsync enabled and double-buffering. There
> is no tearing in any other items except the ones with clipping enabled.
> Tearing is especially noticeable on the embedded device. The GPU is a
> PowerVR SGX chip which is tile-based, so the tearing "lines" are actually
> vertical. Also the framerate is mostly somewhere between 30-60.
>
>  Tearing appears maybe 20% of the time spent scrolling.
>
>  I'm wondering if the core issue is this:
>
>  I assume clipping is implemented as rendering the item into a temporary
> texture, and the clipped area is of this is finally rendered to the screen
> buffer. This temporary texture is not double-buffered. This means it would
> be possible that the render pipeline starts writing into a texture (next
> frame) that is being drawing into the screen buffer (current frame).
>
>  Any thoughts? The tearing is really bad sometimes, and I don't really
> have the option of disabling clipping either.
>
>  Cheers,
> Ola
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.qt-project.org/pipermail/interest/attachments/20131113/c76c2e25/attachment.html>