Viewer: PSI logo links to psi.ch, inverted in dark theme, sized to the menu bar

The logo is black only, so the dark-theme negative is the same image with
its colours inverted, redrawn on every theme change. It is now a flat tool
button opening https://www.psi.ch. Button padding is removed and the logo
is scaled to the menu bar's natural height, so it no longer makes the bar
taller than its entries.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

viewer/JFJochViewerWindow.cpp

@@ -26,6 +26,9 @@
 #include <QLabel>
 #include <QPainter>
 #include <QPushButton>
+#include <QToolButton>
+#include <QDesktopServices>
+#include <QUrl>
 
 #include <utility>
 
@@ -37,6 +40,7 @@
 #include "widgets/JFJochViewerSettingsDock.h"
 #include "widgets/JFJochViewerFileBrowser.h"
 #include "JFJochViewerStatusBar.h"
+#include "ViewerTheme.h"
 #include "../common/CUDAWrapper.h"
 #include "../rugnux/RugnuxDefaults.h"
 #include "windows/JFJochViewerImageListWindow.h"
@@ -71,14 +75,31 @@ JFJochViewerWindow::JFJochViewerWindow(QWidget *parent, bool dbus, const QString
     menuBar = new JFJochViewerMenu(this);
     setMenuBar(menuBar);
 
-    // PSI logo in the menu-bar corner. There are four interchangeable dot designs; pick one at
-    // random each launch, for fun.
+    // PSI logo in the menu-bar corner, linking to the PSI website. There are four interchangeable dot
+    // designs; pick one at random each launch, for fun. The logo is black only, so the negative for the
+    // dark theme is the same image with its colours inverted.
     {
         const int n = QRandomGenerator::global()->bounded(1, 5);   // 1..4
-        QPixmap logoPixmap(QStringLiteral(":/psi_%1.png").arg(n, 2, 10, QLatin1Char('0')));
-        auto *logo = new QLabel(this);
-        logo->setPixmap(logoPixmap.scaledToHeight(22, Qt::SmoothTransformation));
-        logo->setContentsMargins(6, 0, 8, 0);
+        // As tall as the menu entries make the bar, so the logo does not stretch it.
+        const QImage logoImage = QImage(QStringLiteral(":/psi_%1.png").arg(n, 2, 10, QLatin1Char('0')))
+                .convertToFormat(QImage::Format_ARGB32)
+                .scaledToHeight(menuBar->sizeHint().height(), Qt::SmoothTransformation);
+        auto *logo = new QToolButton(this);
+        logo->setAutoRaise(true);
+        // No button padding or frame, which would make the bar taller all the same.
+        logo->setStyleSheet("QToolButton { padding: 0px 8px 0px 6px; border: none; }");
+        logo->setCursor(Qt::PointingHandCursor);
+        logo->setToolTip("Paul Scherrer Institute - www.psi.ch");
+        logo->setIconSize(logoImage.size());
+        auto setLogoIcon = [logo, logoImage] {
+            QImage image = logoImage;
+            if (DarkTheme())
+                image.invertPixels(QImage::InvertRgb);
+            logo->setIcon(QPixmap::fromImage(image));
+        };
+        setLogoIcon();
+        connect(ThemeNotifier::Instance(), &ThemeNotifier::changed, logo, setLogoIcon);
+        connect(logo, &QToolButton::clicked, [] { QDesktopServices::openUrl(QUrl("https://www.psi.ch")); });
         menuBar->setCornerWidget(logo, Qt::TopRightCorner);
     }