[Client] Graph connection latency history in the status bar

Add LatencyGraphWidget, a size-agnostic bar sparkline over the rolling
sample window: heights scale to the window's own range while colors map
onto an absolute quality ramp, so a steady good ping stays green. Embed
it in the new LatencyStatusWidget together with the textual ping
readout and feed both through ConnectionController's forwarded signals;
the whole area hides while disconnected or without samples.

Took 9 minutes

Took 14 seconds

cockatrice/CMakeLists.txt

@@ -15,6 +15,8 @@ set(cockatrice_SOURCES
     src/client/network/update/client/client_update_checker.cpp
     src/client/network/update/client/release_channel.cpp
     src/client/network/update/card_spoiler/spoiler_background_updater.cpp
+    src/client/latency_graph_widget.cpp
+    src/client/latency_status_widget.cpp
     src/client/lag_monitor.cpp
     src/client/sound_engine.cpp
     src/client/settings/cache_settings.cpp

cockatrice/src/client/latency_graph_widget.cpp

@@ -0,0 +1,52 @@
+/**
+ * @file latency_graph_widget.cpp
+ * @ingroup Client
+ */
+
+#include "latency_graph_widget.h"
+
+#include <QPainter>
+
+LatencyGraphWidget::LatencyGraphWidget(QWidget *parent) : QWidget(parent)
+{
+}
+
+void LatencyGraphWidget::setSamples(const QList<int> &samplesMs)
+{
+    samples = samplesMs;
+    update();
+}
+
+void LatencyGraphWidget::paintEvent(QPaintEvent * /* event */)
+{
+    if (samples.isEmpty()) {
+        return;
+    }
+
+    QPainter painter(this);
+
+    // Heights are relative to the window's own worst sample (floored at
+    // MinScaleMs) so the shape of the variance stays readable even when every
+    // value is small.
+    qint64 heightScaleMs = MinScaleMs;
+    for (int sample : samples) {
+        heightScaleMs = qMax(heightScaleMs, static_cast<qint64>(sample));
+    }
+
+    const qreal widthPerBar = static_cast<qreal>(width()) / samples.size();
+    for (int i = 0; i < samples.size(); ++i) {
+        const qreal heightRatio = qBound(0.0, static_cast<double>(samples.at(i)) / heightScaleMs, 1.0);
+        const qreal barHeight = heightRatio * height();
+
+        // Colors follow an absolute quality ramp: a steady good ping stays
+        // green no matter how uniform the window is.
+        const qreal colorRatio = qBound(0.0, static_cast<double>(samples.at(i)) / ColorScaleMs, 1.0);
+        QColor color;
+        color.setHsv(qRound(120.0 * (1.0 - colorRatio)), 255, 255);
+
+        const QRectF bar(static_cast<qreal>(i) * widthPerBar + 1.0,
+                         static_cast<qreal>(height()) - barHeight,
+                         qMax(1.0, widthPerBar - 2.0), barHeight);
+        painter.fillRect(bar, color);
+    }
+}

cockatrice/src/client/latency_graph_widget.h

@@ -0,0 +1,43 @@
+/**
+ * @file latency_graph_widget.h
+ * @ingroup Client
+ */
+
+#ifndef LATENCY_GRAPH_WIDGET_H
+#define LATENCY_GRAPH_WIDGET_H
+
+#include <QList>
+#include <QWidget>
+
+/**
+ * @brief Bar graph of recent network round-trip samples.
+ *
+ * Draws one bar per sample, oldest on the left. Bar height is relative to the
+ * window's own scale so the shape of the variance stays readable, while bar
+ * color maps each sample onto an absolute quality ramp (green at rest through
+ * red at ColorScaleMs) so a steady good ping never looks alarming. Size
+ * agnostic: the status bar embeds a small instance while the latency detail
+ * popup shows a large one.
+ */
+class LatencyGraphWidget : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit LatencyGraphWidget(QWidget *parent = nullptr);
+
+    /// Sample in milliseconds that maps to a fully red bar.
+    static constexpr qint64 ColorScaleMs = 500;
+
+    void setSamples(const QList<int> &samplesMs);
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+
+private:
+    /// Floor of the vertical scale in milliseconds. Keeps small windows readable.
+    static constexpr qint64 MinScaleMs = 100;
+
+    QList<int> samples;
+};
+
+#endif

cockatrice/src/client/latency_status_widget.cpp

@@ -0,0 +1,50 @@
+/**
+ * @file latency_status_widget.cpp
+ * @ingroup Client
+ */
+
+#include "latency_status_widget.h"
+
+#include "latency_graph_widget.h"
+
+#include <QHBoxLayout>
+#include <QLabel>
+
+LatencyStatusWidget::LatencyStatusWidget(QWidget *parent) : QWidget(parent)
+{
+    pingLabel = new QLabel(this);
+    pingLabel->setAccessibleName(tr("Ping"));
+
+    latencyGraph = new LatencyGraphWidget(this);
+    latencyGraph->setFixedSize(90, 14);
+
+    auto *layout = new QHBoxLayout(this);
+    layout->setContentsMargins(0, 0, 0, 0);
+    layout->setSpacing(4);
+    layout->addWidget(latencyGraph);
+    layout->addWidget(pingLabel);
+
+    hide();
+}
+
+void LatencyStatusWidget::updateStats(int lastMs, int medianMs, int p95Ms, int maxMs, int sampleCount)
+{
+    if (sampleCount == 0) {
+        hide();
+        return;
+    }
+
+    const QString stats = tr("Connection quality over the last %n sample(s):", "", sampleCount) + "\n" +
+                          tr("Last: %1 ms").arg(lastMs) + "\n" + tr("Median: %1 ms").arg(medianMs) + "\n" +
+                          tr("95th percentile: %1 ms").arg(p95Ms) + "\n" + tr("Maximum: %1 ms").arg(maxMs);
+
+    pingLabel->setText(tr("Ping: %1 ms").arg(lastMs));
+    pingLabel->setToolTip(stats);
+    pingLabel->setAccessibleDescription(stats);
+    show();
+}
+
+void LatencyStatusWidget::updateSamples(const QList<int> &samplesMs)
+{
+    latencyGraph->setSamples(samplesMs);
+}

cockatrice/src/client/latency_status_widget.h

@@ -0,0 +1,38 @@
+/**
+ * @file latency_status_widget.h
+ * @ingroup Client
+ */
+
+#ifndef LATENCY_STATUS_WIDGET_H
+#define LATENCY_STATUS_WIDGET_H
+
+#include <QList>
+#include <QWidget>
+
+class QLabel;
+class LatencyGraphWidget;
+
+/**
+ * @brief Status bar presentation of server round-trip health.
+ *
+ * Combines the textual "Ping" readout with a small LatencyGraphWidget
+ * sparkline of the rolling sample window. Stays hidden while disconnected or
+ * before any samples exist. Owns all latency display state so MainWindow only
+ * needs to forward two signals here.
+ */
+class LatencyStatusWidget : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit LatencyStatusWidget(QWidget *parent = nullptr);
+
+public slots:
+    void updateStats(int lastMs, int medianMs, int p95Ms, int maxMs, int sampleCount);
+    void updateSamples(const QList<int> &samplesMs);
+
+private:
+    QLabel *pingLabel = nullptr;
+    LatencyGraphWidget *latencyGraph = nullptr;
+};
+
+#endif

cockatrice/src/interface/window_main.cpp

@@ -19,6 +19,7 @@
  ***************************************************************************/
 #include "window_main.h"
 
+#include "../client/latency_status_widget.h"
 #include "../client/network/update/client/client_update_checker.h"
 #include "../client/network/update/client/release_channel.h"
 #include "../client/settings/cache_settings.h"
@@ -145,23 +146,6 @@ void MainWindow::statusChanged(ClientStatus _status)
     }
 }
 
-void MainWindow::updatePingDisplay(int lastMs, int medianMs, int p95Ms, int maxMs, int sampleCount)
-{
-    if (!pingLabel || sampleCount == 0) {
-        if (pingLabel) {
-            pingLabel->hide();
-        }
-        return;
-    }
-
-    pingLabel->setText(tr("Ping: %1 ms").arg(lastMs));
-    pingLabel->setToolTip(tr("Connection quality over the last %n sample(s):", "", sampleCount) + "\n" +
-                          tr("Last: %1 ms").arg(lastMs) + "\n" + tr("Median: %1 ms").arg(medianMs) + "\n" +
-                          tr("95th percentile: %1 ms").arg(p95Ms) + "\n" + tr("Maximum: %1 ms").arg(maxMs));
-    pingLabel->setAccessibleDescription(pingLabel->toolTip());
-    pingLabel->show();
-}
-
 // Actions
 
 void MainWindow::actConnect()
@@ -553,11 +537,13 @@ MainWindow::MainWindow(QWidget *parent)
             [this](bool show) { statusBar()->setVisible(show); });
     statusBar()->setVisible(SettingsCache::instance().userInterface().getShowStatusBar());
 
-    pingLabel = new QLabel(this);
-    pingLabel->setAccessibleName(tr("Ping"));
-    pingLabel->hide();
-    statusBar()->addPermanentWidget(pingLabel);
-    connect(connectionController, &ConnectionController::pingStatsUpdated, this, &MainWindow::updatePingDisplay);
+    latencyStatus = new LatencyStatusWidget(this);
+    statusBar()->addPermanentWidget(latencyStatus);
+
+    connect(connectionController, &ConnectionController::pingStatsUpdated, latencyStatus,
+            &LatencyStatusWidget::updateStats);
+    connect(connectionController, &ConnectionController::pingSamplesUpdated, latencyStatus,
+            &LatencyStatusWidget::updateSamples);
 
     connect(&SettingsCache::instance().shortcuts(), &ShortcutsSettings::shortCutChanged, this,
             &MainWindow::refreshShortcuts);

cockatrice/src/interface/window_main.h

@@ -51,6 +51,7 @@ class HandlePublicServers;
 class LocalClient;
 class LocalServer;
 class QLabel;
+class LatencyStatusWidget;
 class QThread;
 class RemoteClient;
 class ServerInfo_User;
@@ -73,7 +74,6 @@ public slots:
 private slots:
     void updateTabMenu(const QList<QMenu *> &newMenuList);
     void statusChanged(ClientStatus _status);
-    void updatePingDisplay(int lastMs, int medianMs, int p95Ms, int maxMs, int sampleCount);
     void localGameEnded();
     void pixmapCacheSizeChanged(int newSizeInMBs);
     void actDisconnect();
@@ -148,8 +148,8 @@ private:
     WndSets *wndSets;
     ConnectionController *connectionController;
     LocalServer *localServer;
-    QLabel *pingLabel = nullptr; ///< status bar label with live round-trip stats
     LagMonitor lagMonitor; ///< watches the main thread for event loop stalls
+    LatencyStatusWidget *latencyStatus = nullptr; ///< status bar widget with live round-trip stats and history graph
     bool bHasActivated, askedForDbUpdater;
     QProcess *cardUpdateProcess;
     DlgViewLog *logviewDialog;