Previous frames get rendered every now and then

[rourunisen]

Every so often an earlier frame gets shown instead of the one I’m supposed to see. This means that for example, as happened to me today, after pressing the button to show the backside of the first card in a session, I am presented with the frame of the deckoverview instead. Doing an action that causes a rerender, like selecting text, will cause the correct frame to show.

I had this happen both on my PC with a NVIDEA GPU, and on my laptop with internal graphics. It also happens regardless of backend, though I think it happens less on Vulkan. I have noticed that it seems to appear less often on more powerful devices. After I upgraded my laptop, the frequency of this decreased, but when my laptop slows down (like it often does currently because its unbearably hot), it happens 1-2 times a day.

It doesn’t usually happen on my more simple cards, like those that just use a variant of the basic template, however, it does happen with those that have more text, html-tags and logic frequently.

My guess is that there is double (or triple?) buffering going on and that, if a certain part of the logic on the CPU is too slow, the old frame gets swapped in instead of the new one. If that is the case, some sort of synchronization might be necessary, though I have no idea about QT.

[Danika_Dakika]

This issue is usually solved by changing video drivers – #6 on the Troubleshooting Checklist. It isn’t clear whether you’ve tried all of the ones available in Tools > Preferences and restarted after each switch.

[rourunisen]

Thank you for the reply. I have tried all of them and did notice that it happens less on Vulkan, however it happens regardless even when using software rendering, on different devices with different GPU makers.

[Danika_Dakika]

Thanks for clarifying that.

• What Anki version are you using – and is it Qt5 or Qt6? What OS?
• If it’s NVIDIA-related, did you search the forum for other issues to see if any of them sound similar to yours?
• For the cards where this happens (“those that have more text, html-tags …”) – how complex are they? Do they include scripts too, or are they just longer? Are they being made by the same note type?
• Have you tried the rest of the Troubleshooting Checklist – especially disabling add-ons (#2)?

[rourunisen]

• I’m running Anki 24.06.3 (d678e393)⁩ QT6 on Windows 11 23H2, though I have this problem all the way from when QT5 was the only option yet.
• It also happens on an Intel GPU and when software rendering, so I don’t think it is related to that.
• I will attach the card type below, it is not terribly complicated but certainly more than the basic-note type. On basic cards it basically never happens. The notetype for the card where frequency is the highest has 10 fields.
• I’ve tried that and specifically to no effect EXCEPT Auto Ease Factor when I still used that. As in, when I stopped using it in favor for FSRS, the frequency went noticibly down.

Front:

<span class="expression">{{kanji}}</span>

<br>
<br>
<p class="meaning-label">意味</p>

Back:

{{FrontSide}}

{{#variant}}
<div class="centered-block" style="margin-bottom: 0.5em;">
	<div>
			<div class="variant">
				<span class="variant-label">異体字:</span>
				<span class="variant-character">{{variant}}</span>
			</div>
	</div>
</div>

<br>
{{/variant}}

<div class="centered-block"  style="max-width: 70em">
	
	<span class="meaning">{{meaning}}</span>
</div>

<script>
document.getElementById("typeans").style.fontSize = "1.6em";
</script>

<hr style="margin-top: 5em;">
<p style="text-align:left;">
&nbsp;&nbsp;&nbsp;&nbsp;
<span class="big"><b>部首</b> {{radical}}</span>
<span style="float:right;"><span class="big"><b>漢検の級</b> {{level}}</span> 
&nbsp;&nbsp;&nbsp;&nbsp;
</span></p>

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<div class=big><div class=left><hr><b>筆順</b> ({{strokes}}画)</div></div>

{{stroke order}}<hr></div>
-->

Style:

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 font-family: arial;
 font-size: 20px;
 text-align: center;
 color: black;
 background-color: white;
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ruby rt { visibility: hidden; }

ruby:hover rt { visibility: visible; }


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.big {
 font-size: 25px;
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.外{color:#686868;}

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.meaning {
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	text-align: center;
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	font-size: 1.4em;
	background-color: teal;
	padding: 0.2em;
}

.centered-block {
    display: inline-block;
    text-align: left;
    /* Uncomment if you want to set the maximum width of the block */
    /* max-width: 60vw; */
}

.meaning img { /* make images not take up to much vertical space */
	max-height: 6em;
}

.index {
  font-size: 1rem;
}

.story {
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	display: block;
}

[dae]

I’m surprised it happens even with the software driver - you made sure to restart each time you changed the driver? The only other suggestion I have is to try upgrading your video drivers, if they’re not the latest.

[rourunisen]

In the time I have had this issue, I have tried various drivers and I think they didn’t seem to effect anything.

My guess would be a race condition that triggers between qt switching out the frames and chromium (or webkit?) presenting its next rendered one. That wouldn’t explain though why the flip card button also stays the same. In some rare cases I have had it that the card stays the same but the buttons appear on one half (good and easy), while the other half is half of the flip card button.

Is there some kind of synchronization missing that leads to a race condition with qt’s double buffering? Maybe something along the lines of: Under some circumstances, the rendering of the next frame takes longer than the ~16ms it takes before the next frame is switched in.

[dae]

This is handled by Qt, not Anki, so I don’t have an answer for you. I do know it only seems to affect users with certain display configurations, but typically changing the driver in Anki is sufficient to solve it.

[rourunisen]

This just happened to me. I had a blank screen and after pressing space, I had a different font and the contents on the left.

I guess this is a bug. How can I report this?

[sorata]

Bugs are almost always triaged here first but there’s also the issue tracker in Anki’s repo. Is this reproducible for you?

[rourunisen]

It happens sporadically. Sometimes I have an entire session without issue, at other times it happens some 2-3 times or more. I’m currently not on my PC, only my laptop, but I could try to record a session and then upload how it looks to be.

I can also upload my deck here if you want, though it is a big large.