commit beab2b6e4adcdab1fd71964c5ab7533c6050edbf
author Pierre Ossman <ossman@cendio.se> Thu Sep 20 10:52:15 2018 +0200
committer Pierre Ossman <ossman@cendio.se> Fri Sep 21 10:38:41 2018 +0200
tree debf0b7f8ad3c74e45a9076531ec5f7b8db0468d
parent ab9fd6b4d5060cd02bfad7846fa5164353f5c277

Allow perceptually lossless refresh

Loosen the definition of "lossless" a bit so that we can use high
quality JPEG to refresh damaged parts of the screen. Although this
isn't bit perfect, it is close enough that most users will not be
able to tell the difference.

Level 9 is used rather than level 8 because some monitors have
exaggerated contrast that allows the artefacts from level 8 to be
noticeable.

common/rfb/EncodeManager.cxx

diff --git a/common/rfb/EncodeManager.cxx b/common/rfb/EncodeManager.cxx
index d783d54..02128f7 100644
--- a/common/rfb/EncodeManager.cxx
+++ b/common/rfb/EncodeManager.cxx
@@ -364,6 +364,8 @@
   enum EncoderClass solid, bitmap, bitmapRLE;
   enum EncoderClass indexed, indexedRLE, fullColour;
 
+  bool allowJPEG;
+
   rdr::S32 preferred;
 
   std::vector<int>::iterator iter;
@@ -371,6 +373,12 @@
   solid = bitmap = bitmapRLE = encoderRaw;
   indexed = indexedRLE = fullColour = encoderRaw;
 
+  allowJPEG = conn->cp.pf().bpp >= 16;
+  if (!allowLossy) {
+    if (encoders[encoderTightJPEG]->losslessQuality == -1)
+      allowJPEG = false;
+  }
+
   // Try to respect the client's wishes
   preferred = conn->getPreferredEncoding();
   switch (preferred) {
@@ -383,8 +391,7 @@
     bitmapRLE = indexedRLE = fullColour = encoderHextile;
     break;
   case encodingTight:
-    if (encoders[encoderTightJPEG]->isSupported() &&
-        (conn->cp.pf().bpp >= 16) && allowLossy)
+    if (encoders[encoderTightJPEG]->isSupported() && allowJPEG)
       fullColour = encoderTightJPEG;
     else
       fullColour = encoderTight;
@@ -401,8 +408,7 @@
   // Any encoders still unassigned?
 
   if (fullColour == encoderRaw) {
-    if (encoders[encoderTightJPEG]->isSupported() &&
-        (conn->cp.pf().bpp >= 16) && allowLossy)
+    if (encoders[encoderTightJPEG]->isSupported() && allowJPEG)
       fullColour = encoderTightJPEG;
     else if (encoders[encoderZRLE]->isSupported())
       fullColour = encoderZRLE;
@@ -460,9 +466,17 @@
     encoder = encoders[*iter];
 
     encoder->setCompressLevel(conn->cp.compressLevel);
-    encoder->setQualityLevel(conn->cp.qualityLevel);
-    encoder->setFineQualityLevel(conn->cp.fineQualityLevel,
-                                 conn->cp.subsampling);
+
+    if (allowLossy) {
+      encoder->setQualityLevel(conn->cp.qualityLevel);
+      encoder->setFineQualityLevel(conn->cp.fineQualityLevel,
+                                   conn->cp.subsampling);
+    } else {
+      int level = __rfbmax(conn->cp.qualityLevel,
+                           encoder->losslessQuality);
+      encoder->setQualityLevel(level);
+      encoder->setFineQualityLevel(-1, subsampleUndefined);
+    }
   }
 }
 
@@ -567,7 +581,9 @@
   encoder = encoders[klass];
   conn->writer()->startRect(rect, encoder->encoding);
 
-  if (encoder->flags & EncoderLossy)
+  if ((encoder->flags & EncoderLossy) &&
+      ((encoder->losslessQuality == -1) ||
+       (encoder->getQualityLevel() < encoder->losslessQuality)))
     lossyRegion.assign_union(Region(rect));
   else
     lossyRegion.assign_subtract(Region(rect));