Show dot when there is no visible cursor

Disabled by default.

app/ui.js

@@ -161,6 +161,7 @@ const UI = {
         UI.initSetting('resize', 'off');
         UI.initSetting('shared', true);
         UI.initSetting('view_only', false);
+        UI.initSetting('show_dot', false);
         UI.initSetting('path', 'websockify');
         UI.initSetting('repeaterID', '');
         UI.initSetting('reconnect', false);
@@ -347,6 +348,8 @@ const UI = {
         UI.addSettingChangeHandler('shared');
         UI.addSettingChangeHandler('view_only');
         UI.addSettingChangeHandler('view_only', UI.updateViewOnly);
+        UI.addSettingChangeHandler('show_dot');
+        UI.addSettingChangeHandler('show_dot', UI.updateShowDotCursor);
         UI.addSettingChangeHandler('host');
         UI.addSettingChangeHandler('port');
         UI.addSettingChangeHandler('path');
@@ -1015,6 +1018,7 @@ const UI = {
 
         UI.rfb = new RFB(document.getElementById('noVNC_container'), url,
                          { shared: UI.getSetting('shared'),
+                           showDotCursor: UI.getSetting('show_dot'),
                            repeaterID: UI.getSetting('repeaterID'),
                            credentials: { password: password } });
         UI.rfb.addEventListener("connect", UI.connectFinished);
@@ -1583,6 +1587,11 @@ const UI = {
         UI.setMouseButton(1); //has it's own logic for hiding/showing
     },
 
+    updateShowDotCursor() {
+        if (!UI.rfb) return;
+        UI.rfb.showDotCursor = UI.getSetting('show_dot');
+    },
+
     updateLogging() {
         WebUtil.init_logging(UI.getSetting('logging'));
     },

core/rfb.js

@@ -48,6 +48,7 @@ export default class RFB extends EventTargetMixin {
         this._rfb_credentials = options.credentials || {};
         this._shared = 'shared' in options ? !!options.shared : true;
         this._repeaterID = options.repeaterID || '';
+        this._showDotCursor = options.showDotCursor || false;
 
         // Internal state
         this._rfb_connection_state = '';
@@ -168,13 +169,17 @@ export default class RFB extends EventTargetMixin {
 
         // Cursor
         this._cursor = new Cursor();
-        this._cursorImage = {
-            rgbaPixels: [],
-            hotx: 0,
-            hoty: 0,
-            w: 0,
-            h: 0,
-        };
+
+        // XXX: TightVNC 2.8.11 sends no cursor at all until Windows changes
+        // it. Result: no cursor at all until a window border or an edit field
+        // is hit blindly. But there are also VNC servers that draw the cursor
+        // in the framebuffer and don't send the empty local cursor. There is
+        // no way to satisfy both sides.
+        //
+        // The spec is unclear on this "initial cursor" issue. Many other
+        // viewers (TigerVNC, RealVNC, Remmina) display an arrow as the
+        // initial cursor instead.
+        this._cursorImage = RFB.cursors.none;
 
         // populate encHandlers with bound versions
         this._encHandlers[encodings.encodingRaw] = RFB.encodingHandlers.RAW.bind(this);
@@ -324,6 +329,12 @@ export default class RFB extends EventTargetMixin {
         }
     }
 
+    get showDotCursor() { return this._showDotCursor; }
+    set showDotCursor(show) {
+        this._showDotCursor = show;
+        this._refreshCursor();
+    }
+
     // ===== PUBLIC METHODS =====
 
     disconnect() {
@@ -426,6 +437,7 @@ export default class RFB extends EventTargetMixin {
         this._target.appendChild(this._screen);
 
         this._cursor.attach(this._canvas);
+        this._refreshCursor();
 
         // Monitor size changes of the screen
         // FIXME: Use ResizeObserver, or hidden overflow
@@ -1617,12 +1629,33 @@ export default class RFB extends EventTargetMixin {
         this._refreshCursor();
     }
 
+    _shouldShowDotCursor() {
+        // Called when this._cursorImage is updated
+        if (!this._showDotCursor) {
+            // User does not want to see the dot, so...
+            return false;
+        }
+
+        // The dot should not be shown if the cursor is already visible,
+        // i.e. contains at least one not-fully-transparent pixel.
+        // So iterate through all alpha bytes in rgba and stop at the
+        // first non-zero.
+        for (let i = 3; i < this._cursorImage.rgbaPixels.length; i += 4) {
+            if (this._cursorImage.rgbaPixels[i]) {
+                return false;
+            }
+        }
+
+        // At this point, we know that the cursor is fully transparent, and
+        // the user wants to see the dot instead of this.
+        return true;
+    }
+
     _refreshCursor() {
-        this._cursor.change(this._cursorImage.rgbaPixels,
-                            this._cursorImage.hotx,
-                            this._cursorImage.hoty,
-                            this._cursorImage.w,
-                            this._cursorImage.h
+        const image = this._shouldShowDotCursor() ? RFB.cursors.dot : this._cursorImage;
+        this._cursor.change(image.rgbaPixels,
+                            image.hotx, image.hoty,
+                            image.w, image.h
         );
     }
 
@@ -2598,3 +2631,21 @@ RFB.encodingHandlers = {
         }
     }
 }
+
+RFB.cursors = {
+    none: {
+        rgbaPixels: new Uint8Array(),
+        w: 0, h: 0,
+        hotx: 0, hoty: 0,
+    },
+
+    dot: {
+        rgbaPixels: new Uint8Array([
+            255, 255, 255, 255,   0,   0,   0, 255, 255, 255, 255, 255,
+              0,   0,   0, 255,   0,   0,   0,   0,   0,   0,  0,  255,
+            255, 255, 255, 255,   0,   0,   0, 255, 255, 255, 255, 255,
+        ]),
+        w: 3, h: 3,
+        hotx: 1, hoty: 1,
+    }
+};

docs/API.md

@@ -53,6 +53,11 @@ protocol stream.
     should be sent whenever the container changes dimensions. Disabled
     by default.
 
+`showDotCursor`
+  - Is a `boolean` indicating whether a dot cursor should be shown
+    instead of a zero-sized or fully-transparent cursor if the server
+    sets such invisible cursor. Disabled by default.
+
 `capabilities` *Read only*
   - Is an `Object` indicating which optional extensions are available
     on the server. Some methods may only be called if the corresponding

docs/EMBEDDING.md

@@ -61,6 +61,9 @@ query string. Currently the following options are available:
 * `resize` - How to resize the remote session if it is not the same size as
   the browser window. Can be one of `off`, `scale` and `remote`.
 
+* `show_dot` - If a dot cursor should be shown when the remote server provides
+  no local cursor, or provides a fully-transparent (invisible) cursor.
+
 * `logging` - The console log level. Can be one of `error`, `warn`, `info` or
   `debug`.
 

vnc.html

@@ -250,6 +250,10 @@
                                 <input id="noVNC_setting_reconnect_delay" type="number" />
                             </li>
                             <li><hr></li>
+                            <li>
+                                <label><input id="noVNC_setting_show_dot" type="checkbox" /> Show Dot when No Cursor</label>
+                            </li>
+                            <li><hr></li>
                             <!-- Logging selection dropdown -->
                             <li>
                                 <label>Logging: