[PULL,1/3] Revert "vnc: allow fall back to RAW encoding"

Commit Message

Gerd Hoffmann Jan. 23, 2020, 2:21 p.m. UTC

This reverts commit de3f7de7f4e257ce44cdabb90f5f17ee99624557.

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 <[e-mail]>
Signed-off-by: Gerd Hoffmann <[e-mail]>
---
 ui/vnc.c | 20 ++------------------
 1 file changed, 2 insertions(+), 18 deletions(-)

Patch

diff --git a/ui/vnc.c b/ui/vnc.c
index 4100d6e4048c..3e8d1f120710 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -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;
 }