fix(gui): fix empty plots on hidden tabs and replot on tab switch

Plots on hidden tabs (e.g. plot_trains on "Define Trains Paths") had
zero-height axisRect from auto margins, preventing data from rendering.

- Set fixed margins on all 3 network plots to ensure positive dimensions
- Add tab-change signal handler to replot nodes/links when tab becomes visible
- Remove redundant replot() calls after data()->clear()

Author: AhmedAredah

src/NeTrainSimGUI/gui/netrainsimmainwindow.cpp

@@ -182,6 +182,13 @@ void NeTrainSim::setupGenerals(){
         this->replotHistoryLinks();
     });
 
+    // Replot when switching tabs so that plots on previously hidden
+    // tabs receive their data once visible and laid out.
+    connect(ui->tabWidget_project, &QTabWidget::currentChanged, [this]() {
+        this->replotHistoryNodes();
+        this->replotHistoryLinks();
+    });
+
     // show error if tables has only 1 row
     connect(ui->table_newNodes, &CustomTableWidget::cannotDeleteRow,
             [this]() {
@@ -287,9 +294,12 @@ void NeTrainSim::setupPage1(){
     // add graphs to the plot
     ui->plot_createNetwork->addGraph();
     ui->plot_createNetwork->addGraph();
-    // disable viewing the axies
+    // disable viewing the axes and remove auto margins so the axis rect
+    // always has positive inner dimensions (even on hidden tabs)
     ui->plot_createNetwork->xAxis->setVisible(false);
     ui->plot_createNetwork->yAxis->setVisible(false);
+    ui->plot_createNetwork->axisRect()->setAutoMargins(QCP::msNone);
+    ui->plot_createNetwork->axisRect()->setMargins(QMargins(5, 5, 5, 5));
 
 
     // get the nodes file
@@ -545,9 +555,12 @@ void NeTrainSim::forceReplotLinks() {
 
 
 void NeTrainSim::setupPage2(){
-    // disable viewing the axies
+    // disable viewing the axes and remove auto margins so the axis rect
+    // always has positive inner dimensions (even on hidden tabs)
     ui->plot_trains->xAxis->setVisible(false);
     ui->plot_trains->yAxis->setVisible(false);
+    ui->plot_trains->axisRect()->setAutoMargins(QCP::msNone);
+    ui->plot_trains->axisRect()->setMargins(QMargins(5, 5, 5, 5));
 
     // show the layout as a default
     ui->widget_oldTrainOD->show();
@@ -759,9 +772,12 @@ void NeTrainSim::setupPage3(){
     simulatorWidgetSizes << 229 << 700;
     ui->splitter_simulator->setSizes(simulatorWidgetSizes);
 
-    // disable viewing the axies
+    // disable viewing the axes and remove auto margins so the axis rect
+    // always has positive inner dimensions (even on hidden tabs)
     ui->plot_simulation->xAxis->setVisible(false);
     ui->plot_simulation->yAxis->setVisible(false);
+    ui->plot_simulation->axisRect()->setAutoMargins(QCP::msNone);
+    ui->plot_simulation->axisRect()->setMargins(QMargins(5, 5, 5, 5));
 
     // add graphs to the plot
     auto nodegraph = ui->plot_simulation->addGraph();
@@ -1514,7 +1530,6 @@ void NeTrainSim::updateNodesPlot(CustomPlot &plot, QVector<double>xData,
 
     // clear the graph data
     graph->data()->clear();
-    plot.replot();
 
     if (xData.size() < 1) { return; }
     if (xData.size() != yData.size()) {
@@ -1576,7 +1591,6 @@ void NeTrainSim::updateNodesPlot(CustomPlot &plot, QVector<double>xData,
     }
 
     plot.resetZoom();
-    //plot.replot();
 };
 
 /**
@@ -1764,11 +1778,11 @@ void NeTrainSim::updateLinksPlot(CustomPlot &plot,
                                  QVector<QString> endNodeIDs) {
     // check if the plot has at least 2 graphs
     if (plot.graphCount() < 2) { return; }
+
     // get the QCPGraph object for the graph in the QCustomPlot
     QCPGraph *graph = plot.graph(1);
 
     graph->data()->clear();
-    plot.replot();
 
     if (startNodeIDs.size() != endNodeIDs.size() ||
         startNodeIDs.size() < 1 || this->networkNodes.size() < 1) {
@@ -1798,8 +1812,8 @@ void NeTrainSim::updateLinksPlot(CustomPlot &plot,
     }
     // set the pen style for the lines
     graph->setPen(QPen(Qt::blue, 2));
+
     plot.resetZoom();
-    //plot.replot();
 };
 
 /**