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Re: [PATCH v1] vnc: fix VNC artifacts

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v1] vnc: fix VNC artifacts
Date: Sat, 18 Jan 2020 07:24:58 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

On 1/17/20 10:43 PM, Cameron Esfahani via wrote:
I’m new to this process, what are the next steps?

Assuming your patch is in a branch named vncfix_v1:

1/ Start new branch based on the commit previous to your patch:

  - git checkout -b vncfix_v2 vncfix_v1~

2/ Revert the offending patch, explain in commit description why:

  - git revert de3f7de7f4e257

3/ Apply the rest of your patch on top, git-cherry-pick is smart to directly use the diff context. Verify the patch is correct and rewrite the commit description:

  - git cherry-pick vncfix_v1

4/ Send the 2 patches as a series to the mailing list

Cameron Esfahani

On Jan 16, 2020, at 11:47 PM, Gerd Hoffmann <address@hidden> wrote:

On Thu, Jan 16, 2020 at 07:50:58PM -0800, Cameron Esfahani wrote:
Remove VNC optimization to reencode framebuffer update as raw if it's
smaller than the default encoding.  QEMU's implementation was naive and
didn't account for the ZLIB z_stream mutating with each compression.  Just
saving and restoring the output buffer offset wasn't sufficient to "rewind"
the previous encoding.  Considering that ZRLE is never larger than raw and
even though ZLIB can occasionally be fractionally larger than raw, the
overhead of implementing this optimization correctly isn't worth it.

So just revert de3f7de7f4e257 then ...

In my investigation, ZRLE always compresses better than ZLIB so
prioritize ZRLE over ZLIB, even if the client hints that ZLIB is

... and make this a separate patch?


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