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List: kwin
Subject: Re: Review Request 109452: Fix v-sync in EGL backend
From: "Ralf Jung" <post+kde () ralfj ! de>
Date: 2013-03-26 20:20:45
Message-ID: 20130326202045.10391.777 () vidsolbach ! de
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> On March 26, 2013, 8:15 a.m., Martin Gräßlin wrote:
> > Looking forward to try that change on the pandaboard as that hardware doesn't \
> > support buffer preservation. So if it neither does buffer preservation nor \
> > eglPostSubBufferNV (haven't checked that one yet, didn't get that far with \
> > testing), it'll be interesting ;-)
Indeed, an interesting testcase. Note that there is no regression here, the previous \
code couldn't work at all without buffer preservation, even if eglPostSubBufferNV was \
present. The only possible solution for such systems is to always re-draw the entire \
frame ('c' or 'p' swap strategy).
- Ralf
-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
http://git.reviewboard.kde.org/r/109452/#review29894
-----------------------------------------------------------
On March 26, 2013, 9:20 p.m., Ralf Jung wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/109452/
> -----------------------------------------------------------
>
> (Updated March 26, 2013, 9:20 p.m.)
>
>
> Review request for kwin, Martin Gräßlin and Thomas Lübking.
>
>
> Description
> -------
>
> This fixes v-sync in the EGL backend. The backend used to always enable \
> EGL_BUFFER_PRESERVED, which means that eglSwapBuffer() will do a copy instead of a \
> page flip - not only is this unnecessarily expensive, it also breaks v-sync. \
> Instead, defer the decision whether to enable EGL_BUFFER_PRESERVED till we know \
> which EGL extensions are available, and enable it only if we do not have \
> eglPostSubBufferNV - that function is needed to do a partial screen update, since \
> the glCopyPixels path we use in the GLX backend does not work.
> I also refactored the copy pixels code into its own function since I planned for \
> the EGL backend to use it - and even though that's not possible, it still avoids \
> code duplication between SceneOpenGL and the GLX backend.
> I added eglWaitNative in prepareRenderingFrame mostly because the GLX backend does \
> that, too, and it is better tested. Is any of these sync functions (eglWaitGL, \
> eglWaitNative, XFlush) really needed?
>
> Diffs
> -----
>
> kwin/eglonxbackend.cpp a0cba91
> kwin/glxbackend.cpp 407c014
> kwin/scene_opengl.h 44e8d15
> kwin/scene_opengl.cpp 43b326c
>
> Diff: http://git.reviewboard.kde.org/r/109452/diff/
>
>
> Testing
> -------
>
> Tested a few settings for glPreferBuffer Swap (e, p, c), they all seem to behave as \
> expected: No tearing at all for p and c, tearing only for small updates when using \
> e.
>
> Thanks,
>
> Ralf Jung
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="http://git.reviewboard.kde.org/r/109452/">http://git.reviewboard.kde.org/r/109452/</a>
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<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <p style="margin-top: 0;">On March 26th, 2013, 8:15 a.m. CET, <b>Martin \
Gräßlin</b> wrote:</p> <blockquote style="margin-left: 1em; border-left: 2px solid \
#d0d0d0; padding-left: 10px;"> <pre style="white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">Looking forward to try that change on the pandaboard as that hardware \
doesn't support buffer preservation. So if it neither does buffer preservation \
nor eglPostSubBufferNV (haven't checked that one yet, didn't get that far \
with testing), it'll be interesting ;-)</pre> </blockquote>
</blockquote>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;">Indeed, an interesting \
testcase. Note that there is no regression here, the previous code couldn't work \
at all without buffer preservation, even if eglPostSubBufferNV was present. The only \
possible solution for such systems is to always re-draw the entire frame ('c' \
or 'p' swap strategy).</pre> <br />
<p>- Ralf</p>
<br />
<p>On March 26th, 2013, 9:20 p.m. CET, Ralf Jung wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="8" \
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url('http://git.reviewboard.kde.org/static/rb/images/review_request_box_top_bg.ab6f3b1072c9.png'); \
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<div>Review request for kwin, Martin Gräßlin and Thomas Lübking.</div>
<div>By Ralf Jung.</div>
<p style="color: grey;"><i>Updated March 26, 2013, 9:20 p.m.</i></p>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">This fixes v-sync in the EGL backend. The backend used to always enable \
EGL_BUFFER_PRESERVED, which means that eglSwapBuffer() will do a copy instead of a \
page flip - not only is this unnecessarily expensive, it also breaks v-sync. Instead, \
defer the decision whether to enable EGL_BUFFER_PRESERVED till we know which EGL \
extensions are available, and enable it only if we do not have eglPostSubBufferNV - \
that function is needed to do a partial screen update, since the glCopyPixels path we \
use in the GLX backend does not work.
I also refactored the copy pixels code into its own function since I planned for the \
EGL backend to use it - and even though that's not possible, it still avoids code \
duplication between SceneOpenGL and the GLX backend.
I added eglWaitNative in prepareRenderingFrame mostly because the GLX backend does \
that, too, and it is better tested. Is any of these sync functions (eglWaitGL, \
eglWaitNative, XFlush) really needed?</pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;">Tested a few settings for glPreferBuffer Swap (e, p, c), they all seem \
to behave as expected: No tearing at all for p and c, tearing only for small updates \
when using e.</pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>kwin/eglonxbackend.cpp <span style="color: grey">(a0cba91)</span></li>
<li>kwin/glxbackend.cpp <span style="color: grey">(407c014)</span></li>
<li>kwin/scene_opengl.h <span style="color: grey">(44e8d15)</span></li>
<li>kwin/scene_opengl.cpp <span style="color: grey">(43b326c)</span></li>
</ul>
<p><a href="http://git.reviewboard.kde.org/r/109452/diff/" style="margin-left: \
3em;">View Diff</a></p>
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