The static OnceCell didn't run destructors, so shift to something
where we can explicitly trigger them to run and clean up the
temporary directory area.
This allows the decoder thread to live only long enough
to decode the full set of frames; we can then store the
leases in memory and pull them in only when there is
a cache miss.
refs: https://github.com/wez/wezterm/issues/3263
Adopt the new blob lease layer to storing and referencing
image files.
This reduces the number of open files needed when
images are being displayed in the terminal.
refs: https://github.com/wez/wezterm/issues/3263
Input data:
\e_Ga=T,f=32,s=10,v=22,c=1,r=1,m=1\e\\e_Gm=1;/xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T//P=\e\\e_Gm=1;/xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T////E////xP///8T//P=\e\\e_Gm=0\e\
There were two issues in handling this:
* We expected there to be `;payload` in the first transmission packet,
but there wasn't one, so we ignored it as ill-formed.
* The standard base64 decoder in the rust ecosystem is super strict
and rejects the "sloppy" python base64 encoder output that isn't
strictly conformant with the RFC. We need to jump through some
hoops to get it to relax and accept the input.
refs: https://github.com/wez/wezterm/issues/2716
Continuing from the previous commit, this shifts:
* In-memory data -> temporary file
* Image decoding -> background thread
The background thread asynchronously decodes frames and
sends them to the render thread via a bounded channel.
While decoding frames, it writes them, uncompressed, to
a scratch file so that when the animation loops, it is
a very cheap operation to rewind and pull that data
from the file, without having to burn CPU to re-decode
the data from the start.
Memory usage is bounded to 4 uncompressed frames while
decoding, then 3 uncompressed frames (triple buffered)
while looping over the rest.
However, disk usage is N uncompressed frames.
refs: https://github.com/wez/wezterm/issues/3263
This makes decoding animation frames a lazy operation, but it
comes at the cost of needing to re-decode the image from scratch
when it loops, because the image crate doesn't provide a way
to rewind its frame iterator.
That initial decode can have a significant time cost; a small
webp file consistently takes 150ms to decode, which is too
much to do inline in the render thread.
Next steps will be to move that cost off the render thread.
In #3260, the candidate animation had a frame delay of 1ms. That is
problematic because there is no hope for wezterm running at 60fps (a
frame delay of ~16ms) to render that without dropping frames.
A consequence of such a short frame delay, coupled with the way that
images are carved up into cells, is that individual cells can easily
become visibled de-synchronized from their neighbors and results in what
looks like mpeg artifacts but are really regions where the cells are a
few frames ahead/behind their neighbors.
The solution is to clamp the frame duration up to match the minimum
displayable frame duration as governed by max_fps.
refs: https://github.com/wez/wezterm/issues/3260
