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Revert "vnc: allow fall back to RAW encoding" 

This reverts commit de3f7de7f4.

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.  Because of the mutation, simply
resetting the output buffer's offset wasn't sufficient to "rewind" the
operation.  The mutated z_stream would generate future zlib blocks which
referred to symbols in past blocks which weren't sent.  This would lead
to artifacting.

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.

Signed-off-by: Cameron Esfahani <dirty@apple.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
Gerd Hoffmann 2020-01-21 07:02:10 +01:00
parent 43d1455cf8
commit 0780ec7be8
1 changed files with 2 additions and 18 deletions
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20
ui/vnc.c
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@ -898,8 +898,6 @@ int vnc_raw_send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
int vnc_send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
{
int n = 0;
bool encode_raw = false;
size_t saved_offs = vs->output.offset;
switch(vs->vnc_encoding) {
case VNC_ENCODING_ZLIB:
@ -922,24 +920,10 @@ int vnc_send_framebuffer_update(VncState *vs, int x, int y, int w, int h)
n = vnc_zywrle_send_framebuffer_update(vs, x, y, w, h);
break;
default:
encode_raw = true;
vnc_framebuffer_update(vs, x, y, w, h, VNC_ENCODING_RAW);
n = vnc_raw_send_framebuffer_update(vs, x, y, w, h);
break;
}
/* If the client has the same pixel format as our internal buffer and
* a RAW encoding would need less space fall back to RAW encoding to
* save bandwidth and processing power in the client. */
if (!encode_raw && vs->write_pixels == vnc_write_pixels_copy &&
12 + h * w * VNC_SERVER_FB_BYTES <= (vs->output.offset - saved_offs)) {
vs->output.offset = saved_offs;
encode_raw = true;
}
if (encode_raw) {
vnc_framebuffer_update(vs, x, y, w, h, VNC_ENCODING_RAW);
n = vnc_raw_send_framebuffer_update(vs, x, y, w, h);
}
return n;
}