Handle mirrored monitors on X11

macOS and Windows present mirrored monitors as a single virtual monitor,
but X11 exposes this scenario as two distinct monitors with identical
coordinates. This messes up our logic, and is likely confusing for the
user. So instead we'll ignore any monitors that have identical
coordinates to any already seen monitors.

vncviewer/MonitorArrangement.cxx

 /* Copyright 2021 Hugo Lundin <huglu@cendio.se> for Cendio AB.
+ * Copyright 2021 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
    int x, int y, int w, int h)
 :  Fl_Group(x, y, w, h),
    SELECTION_COLOR(fl_lighter(FL_BLUE)),
-   AVAILABLE_COLOR(fl_lighter(fl_lighter(fl_lighter(FL_BACKGROUND_COLOR)))),
-   monitors()
+   AVAILABLE_COLOR(fl_lighter(fl_lighter(fl_lighter(FL_BACKGROUND_COLOR))))
 {
   // Used for required monitors.
   Fl::set_boxtype(FL_CHECKERED_BOX, checkered_pattern_draw, 0, 0, 0, 0);
 std::set<int> MonitorArrangement::get()
 {
   std::set<int> indices;
+  MonitorMap::const_iterator iter;
 
-  for (int i = 0; i < (int) monitors.size(); i++) {
-    if (monitors[i]->value() == 1)
-      indices.insert(i);
+  for (iter = monitors.begin(); iter != monitors.end(); ++iter) {
+    if (iter->second->value() == 1)
+      indices.insert(iter->first);
   }
 
   return indices;
 
 void MonitorArrangement::set(std::set<int> indices)
 {
-  for (int i = 0; i < (int) monitors.size(); i++) {
-    bool selected = std::find(indices.begin(), indices.end(), i) != indices.end();
-    monitors[i]->value(selected ? 1 : 0);
+  MonitorMap::const_iterator iter;
+
+  for (iter = monitors.begin(); iter != monitors.end(); ++iter) {
+    bool selected = std::find(indices.begin(), indices.end(),
+                              iter->first) != indices.end();
+    iter->second->value(selected ? 1 : 0);
   }
 }
 
 void MonitorArrangement::draw()
 {
-  for (int i = 0; i < (int) monitors.size(); i++) {
-    Fl_Button * monitor = monitors[i];
+  MonitorMap::const_iterator iter;
+
+  for (iter = monitors.begin(); iter != monitors.end(); ++iter) {
+    Fl_Button * monitor = iter->second;
 
-    if (is_required(i)) {
+    if (is_required(iter->first)) {
       monitor->box(FL_CHECKERED_BOX);
       monitor->color(SELECTION_COLOR);
     } else {
   std::pair<int, int> offset = this->offset();
 
   for (int i = 0; i < Fl::screen_count(); i++) {
+    bool match;
+
     Fl::screen_xywh(x, y, w, h, i);
 
+    // Only keep a single entry for mirrored screens
+    match = false;
+    for (int j = 0; j < i; j++) {
+        int x2, y2, w2, h2;
+
+        Fl::screen_xywh(x2, y2, w2, h2, j);
+
+        if ((x != x2) || (y != y2) || (w != w2) || (h != h2))
+            continue;
+
+        match = true;
+        break;
+    }
+    if (match)
+        continue;
+
     Fl_Button *monitor = new Fl_Button(
       /* x = */ this->x() + offset.first + x*scale + (1 - MARGIN_SCALE_FACTOR)*x*scale,
       /* y = */ this->y() + offset.second +  y*scale + (1 - MARGIN_SCALE_FACTOR)*y*scale,
     monitor->callback(monitor_pressed, this);
     monitor->type(FL_TOGGLE_BUTTON);
     monitor->when(FL_WHEN_CHANGED);
-    monitors.push_back(monitor);
+    monitor->copy_tooltip(description(i).c_str());
+    monitors[i] = monitor;
   }
-
-  for (int i = 0; i < (int) monitors.size(); i++)
-    monitors[i]->copy_tooltip(description(i).c_str());
 }
 
 void MonitorArrangement::refresh()
 
 std::string MonitorArrangement::description(int m)
 {
-  assert(m < (int) monitors.size());
+  assert(m < Fl::screen_count());
   const size_t name_len = 1024;
   char name[name_len] = {};
   int bytes_written = get_monitor_name(m, name, name_len);

vncviewer/MonitorArrangement.h

 /* Copyright 2021 Hugo Lundin <huglu@cendio.se> for Cendio AB.
+ * Copyright 2021 Pierre Ossman for Cendio AB
  *
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
 #define __MONITOR_ARRANGEMENT_H__
 
 #include <string>
+#include <map>
+#include <set>
 
 class Fl_Group;
 class Fl_Button;
 private:
   const Fl_Color SELECTION_COLOR;
   const Fl_Color AVAILABLE_COLOR;
-  std::vector<Fl_Button *> monitors;
+  typedef std::map<int, Fl_Button *> MonitorMap;
+  MonitorMap monitors;
 
   // Layout the monitor arrangement.
   void layout();

vncviewer/MonitorIndicesParameter.cxx

 /* Copyright 2021 Hugo Lundin <huglu@cendio.se> for Cendio AB.
+ * Copyright 2021 Pierre Ossman for Cendio AB
  * 
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
     // Start by creating a struct for every monitor.
     for (int i = 0; i < Fl::screen_count(); i++) {
         Monitor monitor = {0};
+        bool match;
 
         // Get the properties of the monitor at the current index;
         Fl::screen_xywh(
             i
         );
 
+        // Only keep a single entry for mirrored screens
+        match = false;
+        for (int j = 0; j < ((int) monitors.size()); j++) {
+            if (monitors[i].x != monitor.x)
+                continue;
+            if (monitors[i].y != monitor.y)
+                continue;
+            if (monitors[i].w != monitor.w)
+                continue;
+            if (monitors[i].h != monitor.h)
+                continue;
+
+            match = true;
+            break;
+        }
+        if (match)
+            continue;
+
         monitor.fltkIndex = i;
         monitors.push_back(monitor);
     }