Qt: fix tracer and selection of packet in IO Graph

Do not assume first graph in the list, pick the first visible graph.
This (1) fixes the tracer which would otherwise show a marker at an
non-obvious position that is not located on the graph and (2) fixes the
GoToPacket action when clicking on the graph.

Bug: 13537
Change-Id: I49d750102ad25c8539aa2e44fe1583cd535dd471
Reviewed-on: https://code.wireshark.org/review/20768
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Peter Wu <peter@lekensteyn.nl>

ui/qt/io_graph_dialog.cpp

@@ -708,6 +708,32 @@ void IOGraphDialog::toggleTracerStyle(bool force_default)
     ui->ioPlot->replot();
 }
 
+// Returns the IOGraph which is most likely to be used by the user. This is the
+// currently selected, visible graph or the first visible graph otherwise.
+IOGraph *IOGraphDialog::currentActiveGraph() const
+{
+    QTreeWidgetItem *selectedItem = ui->graphTreeWidget->currentItem();
+    if (selectedItem && selectedItem->checkState(name_col_) != Qt::Checked) {
+        selectedItem = NULL;
+    }
+
+    if (!selectedItem) {
+        for (int i = 0; i < ui->graphTreeWidget->topLevelItemCount(); i++) {
+            QTreeWidgetItem *item = ui->graphTreeWidget->topLevelItem(i);
+            if (item && item->checkState(name_col_) == Qt::Checked) {
+                selectedItem = item;
+                break;
+            }
+        }
+    }
+
+    if (selectedItem) {
+        return VariantPointer<IOGraph>::asPtr(selectedItem->data(name_col_, Qt::UserRole));
+    } else {
+        return NULL;
+    }
+}
+
 // Scan through our graphs and gather information.
 // QCPItemTracers can only be associated with QCPGraphs. Find the first one
 // and associate it with our tracer. Set bar stacking order while we're here.
@@ -718,15 +744,15 @@ void IOGraphDialog::getGraphInfo()
     start_time_ = 0.0;
 
     tracer_->setGraph(NULL);
+    IOGraph *selectedGraph = currentActiveGraph();
     for (int i = 0; i < ui->graphTreeWidget->topLevelItemCount(); i++) {
         QTreeWidgetItem *item = ui->graphTreeWidget->topLevelItem(i);
-        IOGraph *iog = NULL;
-        if (item) {
-            iog = VariantPointer<IOGraph>::asPtr(item->data(name_col_, Qt::UserRole));
+        if (item && item->checkState(name_col_) == Qt::Checked) {
+            IOGraph *iog = VariantPointer<IOGraph>::asPtr(item->data(name_col_, Qt::UserRole));
             QCPGraph *graph = iog->graph();
             QCPBars *bars = iog->bars();
             int style = item->data(style_col_, Qt::UserRole).toInt();
-            if (graph && !base_graph_) {
+            if (graph && (!base_graph_ || iog == selectedGraph)) {
                 base_graph_ = graph;
             } else if (bars && style == IOGraph::psStackedBar && iog->visible()) {
                 bars->moveBelow(NULL); // Remove from existing stack
@@ -885,11 +911,7 @@ void IOGraphDialog::mouseMoved(QMouseEvent *event)
         if (event && tracer_->graph()) {
             tracer_->setGraphKey(iop->xAxis->pixelToCoord(event->pos().x()));
             ts = tracer_->position->key();
-
-            QTreeWidgetItem *ti = ui->graphTreeWidget->topLevelItem(0);
-            IOGraph *iog = NULL;
-            if (ti) {
-                iog = VariantPointer<IOGraph>::asPtr(ti->data(name_col_, Qt::UserRole));
+            if (IOGraph *iog = currentActiveGraph()) {
                 interval_packet = iog->packetFromTime(ts);
             }
         }

ui/qt/io_graph_dialog.h

@@ -208,6 +208,7 @@ public slots:
     void loadProfileGraphs();
     void makeCsv(QTextStream &stream) const;
     bool saveCsv(const QString &file_name) const;
+    IOGraph *currentActiveGraph() const;
 
 private slots:
     void updateWidgets();