adds qualityLevel property to RFB class for updating JPEG quality level encoding on the fly

core/rfb.js

@@ -275,6 +275,8 @@ export default class RFB extends EventTargetMixin {
             Log.Warn("Specifying showDotCursor as a RFB constructor argument is deprecated");
             this._showDotCursor = options.showDotCursor;
         }
+
+        this._qualityLevel = 6;
     }
 
     // ===== PROPERTIES =====
@@ -337,6 +339,26 @@ export default class RFB extends EventTargetMixin {
     get background() { return this._screen.style.background; }
     set background(cssValue) { this._screen.style.background = cssValue; }
 
+    get qualityLevel() {
+        return this._qualityLevel;
+    }
+    set qualityLevel(qualityLevel) {
+        if (!Number.isInteger(qualityLevel) || qualityLevel < 0 || qualityLevel > 9) {
+            Log.Error("qualityLevel must be an integer between 0 and 9");
+            return;
+        }
+
+        if (this._qualityLevel === qualityLevel) {
+            return;
+        }
+
+        this._qualityLevel = qualityLevel;
+
+        if (this._rfb_connection_state === 'connected') {
+            this._sendEncodings();
+        }
+    }
+
     // ===== PUBLIC METHODS =====
 
     disconnect() {
@@ -1294,7 +1316,7 @@ export default class RFB extends EventTargetMixin {
         encs.push(encodings.encodingRaw);
 
         // Psuedo-encoding settings
-        encs.push(encodings.pseudoEncodingQualityLevel0 + 6);
+        encs.push(encodings.pseudoEncodingQualityLevel0 + this._qualityLevel);
         encs.push(encodings.pseudoEncodingCompressLevel0 + 2);
 
         encs.push(encodings.pseudoEncodingDesktopSize);

core/util/polyfill.js

@@ -1,6 +1,6 @@
 /*
  * noVNC: HTML5 VNC client
- * Copyright (C) 2018 The noVNC Authors
+ * Copyright (C) 2020 The noVNC Authors
  * Licensed under MPL 2.0 or any later version (see LICENSE.txt)
  */
 
@@ -52,3 +52,10 @@ if (typeof Object.assign != 'function') {
         window.CustomEvent = CustomEvent;
     }
 })();
+
+/* Number.isInteger() (taken from MDN) */
+Number.isInteger = Number.isInteger || function isInteger(value) {
+    return typeof value === 'number' &&
+      isFinite(value) &&
+      Math.floor(value) === value;
+};