Improved cursors functionality

Client/WebUI/static/app.js

@@ -225,6 +225,7 @@ function setActiveSig(plotId, key) {
     b.classList.toggle('sig-badge-active', key != null && b.dataset.key === key));
   const p = plots.find(q => q.id === plotId);
   if (p && p.uplot) p.uplot.redraw(false);
+  updatePlotCursorReadouts();
 }
 
 // Mark plots containing key dirty and refresh badge vscale text.
@@ -1287,8 +1288,10 @@ function drawCursorLines(u, p) {
     ctx.fillText(label, px + 14, bbox.top + 2);
     // Per-trace: diamond at crossing point + value label
     if (p) {
-      const DSZ = 5; // diamond half-size in px
+      const activeKey = plotActiveSignal[p.id];
       p.traces.forEach((key, idx) => {
+        const isActive = key === activeKey || (!activeKey && p.traces.length === 1);
+        const DSZ = isActive ? 9 : 5; // diamond half-size in px
         const vNorm = interpAtTime(u, idx + 1, val);
         if (vNorm === null) return;
         const cy = u.valToPos(vNorm, 'y', true);
@@ -2019,10 +2022,56 @@ document.getElementById('btn-cursor').addEventListener('click', () => {
   cursorsDirty = true;
 });
 
+// Format a signal value for the per-plot cursor readout.
+function fmtVal(v) {
+  if (v === null || v === undefined) return '—';
+  return Math.abs(v) >= 10000 ? v.toExponential(2) : parseFloat(v.toPrecision(4)).toString();
+}
+
+// Interpolate the real-unit value of the active/sole signal in plot p at time t.
+function getValueAtCursor(p, t) {
+  if (!p.uplot || t === null) return null;
+  const key = plotActiveSignal[p.id] || (p.traces.length === 1 ? p.traces[0] : null);
+  if (!key) return null;
+  const idx = p.traces.indexOf(key);
+  if (idx < 0) return null;
+  const vNorm = interpAtTime(p.uplot, idx + 1, t);
+  if (vNorm === null) return null;
+  // Un-normalize: y_norm = (y_raw - offset) / divValue + screenPos
+  const vs = sigVScale[p.id + ':' + key];
+  if (!vs) return vNorm;
+  const dv  = vs._resolvedDiv  != null ? vs._resolvedDiv  : (vs.divValue || 1);
+  const ofs = vs._resolvedOffset != null ? vs._resolvedOffset : (vs.offset  || 0);
+  const sp  = vs.screenPos || 0;
+  return (vNorm - sp) * dv + ofs;
+}
+
+// Update per-plot cursor value readouts (A, B, ΔV) for all plots.
+function updatePlotCursorReadouts() {
+  plots.forEach(p => {
+    const el = document.getElementById('pcur-' + p.id);
+    if (!el) return;
+    // Show only when cursors are on and the plot has an active or sole signal.
+    const key = plotActiveSignal[p.id] || (p.traces.length === 1 ? p.traces[0] : null);
+    if (cursors.mode !== 'on' || !key || !p.uplot) {
+      el.style.display = 'none';
+      return;
+    }
+    const vA = getValueAtCursor(p, cursors.tA);
+    const vB = getValueAtCursor(p, cursors.tB);
+    const dv = (vA !== null && vB !== null) ? vB - vA : null;
+    document.getElementById('pcur-a-'  + p.id).textContent = 'A: '  + fmtVal(vA);
+    document.getElementById('pcur-b-'  + p.id).textContent = 'B: '  + fmtVal(vB);
+    document.getElementById('pcur-dv-' + p.id).textContent = 'ΔV: ' + fmtVal(dv);
+    el.style.display = 'flex';
+  });
+}
+
 function updateCursorReadout() {
   const ro = document.getElementById('cursor-readout');
   const active = cursors.mode === 'on';
   ro.classList.toggle('visible', active);
+  updatePlotCursorReadouts();
   if (!active) return;
 
   // Use the current visible x-range to pick the display unit.
@@ -2605,6 +2654,13 @@ function addPlot() {
     <div class="plot-card-header">
       <span class="plot-title" id="ptitle-${id}" title="Click to configure">Plot ${id}</span>
       <div class="sig-badges" id="badges-${id}"></div>
+      <div class="plot-cursor-ro" id="pcur-${id}" style="display:none">
+        <span class="pcur-a" id="pcur-a-${id}">A: —</span>
+        <span class="pcur-sep">│</span>
+        <span class="pcur-b" id="pcur-b-${id}">B: —</span>
+        <span class="pcur-sep">│</span>
+        <span class="pcur-dv" id="pcur-dv-${id}">ΔV: —</span>
+      </div>
     </div>
     <div class="plot-cfg-bar" id="pcfg-${id}" style="display:none">
       <div class="vstb-header">
@@ -2657,6 +2713,7 @@ function addTraceTo(plotId, signalKey) {
   // Recreate uPlot with new series list
   createUPlot(p);
   p.needsRedraw = true;
+  updatePlotCursorReadouts();
 }
 
 function removeTraceFrom(plotId, signalKey) {
@@ -2672,6 +2729,7 @@ function removeTraceFrom(plotId, signalKey) {
   createUPlot(p);
   p.needsRedraw = true;
   if (!p.traces.length) document.querySelector('#hint-' + plotId).style.display = '';
+  updatePlotCursorReadouts();
 }
 
 function addBadge(plotId, key) {
@@ -2843,6 +2901,9 @@ function renderDirtyPlots() {
     zoomGuard = false;
   });
 
+  // Keep per-plot cursor value readouts in sync with live data.
+  if (cursors.mode === 'on') updatePlotCursorReadouts();
+
   requestAnimationFrame(renderDirtyPlots);
 }