vnc: allow fall back to RAW encoding

I have observed that depending on the contents and the encoding it happens
that sending data as RAW sometimes would take less space than the encoded data.
This is especially the case for small updates or areas with high color images.
If sending RAW encoded data is beneficial allow a fall back to RAW encoding
for the framebuffer update.

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/ui/vnc.c b/ui/vnc.c
index 7b37e3b01f1a9fec935fd3b24afc4199ccb9f6a9..166d1b5b5f61f99ab90ee5958a82d6aa90686f24 100644 (file)
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -840,6 +840,8 @@ 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:
@@ -862,10 +864,24 @@ 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:
-            vnc_framebuffer_update(vs, x, y, w, h, VNC_ENCODING_RAW);
-            n = vnc_raw_send_framebuffer_update(vs, x, y, w, h);
+            encode_raw = true;
             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;
 }