vnc: add lossy option

The lossy option can be used to enable lossy compression
methods like gradient or jpeg. This patch disable them by
default.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-options.hx

diff --git a/qemu-options.hx b/qemu-options.hx
index 0d7dd90..40cee70 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -835,6 +835,13 @@
 use the VNC server until the ACLs have been loaded. This can be
 achieved using the @code{acl} monitor command.
 
+@item lossy
+
+Enable lossy compression methods (gradient, JPEG, ...). If this
+option is set, VNC client may receive lossy framebuffer updates
+depending on its encoding settings. Enabling this option can save
+a lot of bandwidth at the expense of quality.
+
 @end table
 ETEXI
 

vnc-encoding-tight.c

diff --git a/vnc-encoding-tight.c b/vnc-encoding-tight.c
index 5b69ff0..c1a292b 100644
--- a/vnc-encoding-tight.c
+++ b/vnc-encoding-tight.c
@@ -228,6 +228,10 @@
     int compression = vs->tight_compression;
     int quality = vs->tight_quality;
 
+    if (!vs->vd->lossy) {
+        return 0;
+    }
+
     if (ds_get_bytes_per_pixel(vs->ds) == 1 ||
         vs->clientds.pf.bytes_per_pixel == 1 ||
         w < VNC_TIGHT_DETECT_MIN_WIDTH || h < VNC_TIGHT_DETECT_MIN_HEIGHT) {

vnc.c

diff --git a/vnc.c b/vnc.c
index 9cf38d1..ccd7aad 100644
--- a/vnc.c
+++ b/vnc.c
@@ -2482,6 +2482,8 @@
 #endif
         } else if (strncmp(options, "acl", 3) == 0) {
             acl = 1;
+        } else if (strncmp(options, "lossy", 5) == 0) {
+            vs->lossy = true;
         }
     }
 

vnc.h

diff --git a/vnc.h b/vnc.h
index 2a9024d..ec90cd3 100644
--- a/vnc.h
+++ b/vnc.h
@@ -33,6 +33,7 @@
 #include "monitor.h"
 #include "audio/audio.h"
 #include <zlib.h>
+#include <stdbool.h>
 
 #include "keymaps.h"
 
@@ -111,6 +112,7 @@
     char *display;
     char *password;
     int auth;
+    bool lossy;
 #ifdef CONFIG_VNC_TLS
     int subauth; /* Used by VeNCrypt */
     VncDisplayTLS tls;