Implemented backend hr resolution data, splitted test gam

Client/WebUI/hub.go

@@ -5,6 +5,9 @@ import (
 	"log"
 	"math"
 	"net/http"
+	"strconv"
+	"strings"
+	"sync"
 	"time"
 
 	"github.com/gorilla/websocket"
@@ -137,7 +140,8 @@ type hubCmd struct {
 }
 
 // Hub is the central broker between UDP clients and WebSocket clients.
-// All map state is accessed exclusively from the Run() goroutine.
+// All map state is accessed exclusively from the Run() goroutine, except
+// ringsMu/rings which are also read by HTTP handler goroutines.
 type Hub struct {
 	clients     map[*wsClient]bool
 	register    chan *wsClient
@@ -147,6 +151,11 @@ type Hub struct {
 	commandCh   chan hubCmd
 
 	sm *SourceManager // set after construction; used for WS-initiated source changes
+
+	// Ring buffers for hi-res zoom data.
+	// ringsMu protects the map structure; each sigRing has its own RWMutex for data.
+	ringsMu sync.RWMutex
+	rings   map[string]*sigRing // "sourceId:signalKey" → ring
 }
 
 // NewHub creates an initialised Hub.
@@ -158,6 +167,75 @@ func NewHub() *Hub {
 		broadcastCh: make(chan []byte, 64),
 		dataCh:      make(chan taggedSample, 256),
 		commandCh:   make(chan hubCmd, 64),
+		rings:       make(map[string]*sigRing),
+	}
+}
+
+// getRing returns the ring buffer for a fully-prefixed signal key, or nil.
+func (h *Hub) getRing(key string) *sigRing {
+	h.ringsMu.RLock()
+	rb := h.rings[key]
+	h.ringsMu.RUnlock()
+	return rb
+}
+
+// HandleZoom serves GET /api/zoom?t0=...&t1=...&n=...&signals=key1,key2
+// It reads from the ring buffers (safe for concurrent access) and returns
+// LTTB-decimated signal data for the requested time range.
+func (h *Hub) HandleZoom(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	t0, err0 := strconv.ParseFloat(q.Get("t0"), 64)
+	t1, err1 := strconv.ParseFloat(q.Get("t1"), 64)
+	if err0 != nil || err1 != nil || t1 <= t0 {
+		http.Error(w, "invalid t0/t1", http.StatusBadRequest)
+		return
+	}
+	// n=0 (or explicit "0") means no LTTB decimation — return all ring data in range.
+	// n omitted / invalid → default 2400 (display quality).
+	var n int
+	if nStr := q.Get("n"); nStr == "" {
+		n = 2400
+	} else {
+		n, _ = strconv.Atoi(nStr)
+		if n <= 0 {
+			n = 1 << 30 // no decimation
+		} else if n < 10 {
+			n = 2400
+		}
+	}
+
+	keys := strings.Split(q.Get("signals"), ",")
+
+	// Collect ring references under a brief RLock.
+	h.ringsMu.RLock()
+	refs := make(map[string]*sigRing, len(keys))
+	for _, k := range keys {
+		k = strings.TrimSpace(k)
+		if k == "" {
+			continue
+		}
+		if rb, ok := h.rings[k]; ok {
+			refs[k] = rb
+		}
+	}
+	h.ringsMu.RUnlock()
+
+	result := make(map[string]sigData, len(refs))
+	for k, rb := range refs {
+		rt, rv := rb.slice(t0, t1)
+		if len(rt) == 0 {
+			continue
+		}
+		dt, dv := lttbDecimate(rt, rv, n)
+		result[k] = sigData{T: dt, V: dv}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if err := json.NewEncoder(w).Encode(map[string]any{
+		"type":    "zoom",
+		"signals": result,
+	}); err != nil {
+		log.Printf("hub: zoom encode: %v", err)
 	}
 }
 
@@ -294,6 +372,14 @@ func (h *Hub) Run() {
 			case "removeSource":
 				delete(sourcesMap, cmd.sourceID)
 				delete(pending, cmd.sourceID)
+				pfxDel := cmd.sourceID + ":"
+				h.ringsMu.Lock()
+				for k := range h.rings {
+					if strings.HasPrefix(k, pfxDel) {
+						delete(h.rings, k)
+					}
+				}
+				h.ringsMu.Unlock()
 				rebuildSources()
 
 			case "setSourceState":
@@ -309,7 +395,7 @@ func (h *Hub) Run() {
 				}
 				src.signals = cmd.sigs
 				src.configSeq++
-				cfgMsg, err := json.Marshal(map[string]interface{}{
+				cfgMsg, err := json.Marshal(map[string]any{
 					"type":     "config",
 					"sourceId": cmd.sourceID,
 					"signals":  cmd.sigs,
@@ -320,6 +406,28 @@ func (h *Hub) Run() {
 				}
 				src.configJS = cfgMsg
 				h.broadcast(cfgMsg)
+				// Rebuild ring buffers for this source.
+				pfxUpd := cmd.sourceID + ":"
+				h.ringsMu.Lock()
+				for k := range h.rings {
+					if strings.HasPrefix(k, pfxUpd) {
+						delete(h.rings, k)
+					}
+				}
+				for _, sig := range cmd.sigs {
+					ne := sig.NumElements()
+					isTemporal := ne > 1 && (sig.TimeMode == TimeModeFirstSample || sig.TimeMode == TimeModeLastSample)
+					if isTemporal {
+						h.rings[pfxUpd+sig.Name] = newSigRing(ringCapTemporal)
+					} else if ne == 1 {
+						h.rings[pfxUpd+sig.Name] = newSigRing(ringCapScalar)
+					} else {
+						for i := 0; i < ne; i++ {
+							h.rings[pfxUpd+arrayKey(sig.Name, i)] = newSigRing(ringCapScalar)
+						}
+					}
+				}
+				h.ringsMu.Unlock()
 
 			case "wsAddSource":
 				if h.sm != nil {
@@ -364,17 +472,25 @@ func (h *Hub) Run() {
 
 // ─── Data serialisation ───────────────────────────────────────────────────────
 
-// maxScalarPoints caps scalar/spatial-array signals per 30 Hz tick.
-// At typical cycle rates (≤10 kHz) a tick accumulates at most ~333 samples,
-// so this cap is almost never hit.
-const maxScalarPoints = 2000
+// maxPushPoints is the LTTB target for data pushed over WebSocket per 30 Hz tick.
+// At 2 k pts/tick × 30 Hz = 60 k pts/s; the 600 k frontend buffer covers ~10 s.
+// Kept deliberately low so the rolling window shows plenty of history even for
+// multi-MHz signals — zoom resolution comes from the ring buffer instead.
+const maxPushPoints = 2_000
 
-// maxTemporalPoints caps temporal-array (packed-burst) signals per 30 Hz tick.
-// Raised significantly vs scalars because temporal arrays carry high-frequency
-// waveforms: at 5 Msps / 5 kHz update rate a tick produces ~167 k samples;
-// sending 20 k points limits the wire to ~320 KB/ch/tick while giving a
-// minimum visible Δt of ≈ 1.6 µs (vs ≈16 µs with the old 2 k cap).
-const maxTemporalPoints = 20000
+// maxRingPoints is the LTTB target written into the ring buffer per tick.
+// At 5 Msps / 5 kHz packet rate ≈ 167 k raw samples/tick → LTTB to 20 k →
+// min Δt ≈ 33 ms / 20 k ≈ 1.65 µs, sufficient for sub-10 µs zoom resolution.
+const maxRingPoints = 20_000
+
+// ringCapTemporal is the ring buffer capacity for temporal-array signals.
+// At 20 k pts/tick × 30 Hz = 600 k pts/s → 6 M cap gives ~10 s of hi-res
+// history — the same temporal coverage as the frontend push buffer.
+const ringCapTemporal = 6_000_000
+
+// ringCapScalar is the ring buffer capacity for scalar / spatial-array signals.
+// At ≤10 kHz → ~333 pts/tick × 30 Hz ≈ 10 k pts/s → ~10 s of history.
+const ringCapScalar = 100_000
 
 // lttbDecimate reduces (tIn, vIn) to at most threshold representative points
 // using the Largest-Triangle-Three-Buckets algorithm.
@@ -510,7 +626,13 @@ func (h *Hub) buildDataMessageForSource(src *sourceHubState, batch []DataSample)
 				}
 			}
 
-			decimT, decimV := lttbDecimate(allT, allV, maxTemporalPoints)
+			// Write hi-res LTTB data to ring for on-demand zoom queries.
+			ringT, ringV := lttbDecimate(allT, allV, maxRingPoints)
+			if rb := h.getRing(pfx + sig.Name); rb != nil {
+				rb.write(ringT, ringV)
+			}
+			// Decimate further for WebSocket push (rolling window).
+			decimT, decimV := lttbDecimate(allT, allV, maxPushPoints)
 			out[pfx+sig.Name] = sigData{T: decimT, V: decimV}
 
 		case n == 1:
@@ -524,6 +646,9 @@ func (h *Hub) buildDataMessageForSource(src *sourceHubState, batch []DataSample)
 				ts = append(ts, float64(s.WallTime.UnixNano())/1e9)
 				vs = append(vs, vals[0])
 			}
+			if rb := h.getRing(pfx + sig.Name); rb != nil {
+				rb.write(ts, vs)
+			}
 			out[pfx+sig.Name] = sigData{T: ts, V: vs}
 
 		default:
@@ -540,6 +665,9 @@ func (h *Hub) buildDataMessageForSource(src *sourceHubState, batch []DataSample)
 					ts = append(ts, float64(s.WallTime.UnixNano())/1e9)
 					vs = append(vs, vals[i])
 				}
+				if rb := h.getRing(key); rb != nil {
+					rb.write(ts, vs)
+				}
 				out[key] = sigData{T: ts, V: vs}
 			}
 		}

Client/WebUI/main.go

@@ -53,6 +53,7 @@ func main() {
 	}
 	http.Handle("/", http.FileServer(http.FS(sub)))
 	http.HandleFunc("/ws", hub.HandleWebSocket)
+	http.HandleFunc("/api/zoom", hub.HandleZoom)
 	http.HandleFunc("/version", func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprint(w, version)
 	})

Client/WebUI/ringbuf.go

@@ -0,0 +1,88 @@
+package main
+
+import "sync"
+
+// sigRing is a fixed-capacity circular buffer storing (time, value) pairs.
+// Writes come from the Hub.Run() goroutine; reads come from HTTP handler goroutines.
+// The embedded RWMutex protects concurrent access.
+type sigRing struct {
+	mu         sync.RWMutex
+	t, v       []float64
+	cap        int
+	head, size int // next write position; current fill
+}
+
+func newSigRing(capacity int) *sigRing {
+	return &sigRing{
+		t:   make([]float64, capacity),
+		v:   make([]float64, capacity),
+		cap: capacity,
+	}
+}
+
+// write appends (tArr[i], vArr[i]) pairs, overwriting oldest entries when full.
+func (rb *sigRing) write(tArr, vArr []float64) {
+	rb.mu.Lock()
+	defer rb.mu.Unlock()
+	for i := 0; i < len(tArr); i++ {
+		rb.t[rb.head] = tArr[i]
+		rb.v[rb.head] = vArr[i]
+		rb.head = (rb.head + 1) % rb.cap
+		if rb.size < rb.cap {
+			rb.size++
+		}
+	}
+}
+
+// slice returns copies of all (t, v) pairs whose timestamp falls in [t0, t1].
+// The returned slices are safe to use after the call without holding any lock.
+func (rb *sigRing) slice(t0, t1 float64) ([]float64, []float64) {
+	rb.mu.RLock()
+	defer rb.mu.RUnlock()
+
+	if rb.size == 0 {
+		return nil, nil
+	}
+	start := 0
+	if rb.size == rb.cap {
+		start = rb.head
+	}
+	physAt := func(k int) int { return (start + k) % rb.cap }
+
+	// Binary search for t0
+	lo, hi := 0, rb.size
+	for lo < hi {
+		m := (lo + hi) >> 1
+		if rb.t[physAt(m)] < t0 {
+			lo = m + 1
+		} else {
+			hi = m
+		}
+	}
+	kStart := lo
+
+	// Binary search for t1
+	lo, hi = kStart, rb.size
+	for lo < hi {
+		m := (lo + hi) >> 1
+		if rb.t[physAt(m)] <= t1 {
+			lo = m + 1
+		} else {
+			hi = m
+		}
+	}
+	kEnd := lo
+
+	n := kEnd - kStart
+	if n <= 0 {
+		return nil, nil
+	}
+	outT := make([]float64, n)
+	outV := make([]float64, n)
+	for i := 0; i < n; i++ {
+		p := physAt(kStart + i)
+		outT[i] = rb.t[p]
+		outV[i] = rb.v[p]
+	}
+	return outT, outV
+}

Client/WebUI/static/app.js

@@ -64,6 +64,11 @@ let zoomGuard = false;
 // Zoom history for Back button (global since plots are zoom-synced)
 const zoomHistory = [];
 
+// zoomData: hi-res data fetched from /api/zoom, keyed by plot id.
+// Each entry: { signals: { key: {t:Float64Array, v:Float64Array} }, t0, t1 }
+const zoomData = {};
+let _zoomFetchTimer = null;
+
 // Cursors A/B — stored in x-axis units of the current mode:
 //   live mode  → Unix seconds
 //   trig mode  → relative seconds from trigger
@@ -248,6 +253,46 @@ function finaliseTriggerCapture() {
   plots.forEach(p => { p.xRange = null; p.needsRedraw = true; });
   if (trig.mode === 'normal' && !trig.stopped)
     setTimeout(() => { if (trig.enabled && trig.mode === 'normal' && !trig.stopped) trigArm(); }, 200);
+
+  // Upgrade the snapshot in the background with full-resolution ring data.
+  // The push buffer has min Δt ≈ 16 µs; the ring provides ≈ 1.65 µs.
+  upgradeTriggerSnapshot(t0, t1, trig.trigTime);
+}
+
+// Fetches full-resolution ring data for the trigger window and replaces the
+// push-buffer entries in trig.snapshot, then re-renders all plots.
+async function upgradeTriggerSnapshot(t0, t1, capturedTrigTime) {
+  // Small delay so the ring receives the last post-trigger samples
+  // (ring write period ≈ 33 ms; 120 ms gives ≥ 3 ticks of margin).
+  await new Promise(r => setTimeout(r, 120));
+  // Abort if a new trigger has fired since we started.
+  if (!trig.snapshot || trig.trigTime !== capturedTrigTime) return;
+
+  const keys = Object.keys(buffers);
+  if (!keys.length) return;
+
+  const url = `/api/zoom?t0=${t0}&t1=${t1}&n=0&signals=${keys.join(',')}`;
+  let ringSignals;
+  try {
+    const resp = await fetch(url);
+    if (!resp.ok) return;
+    const json = await resp.json();
+    ringSignals = json && json.signals;
+  } catch (e) {
+    console.warn('trigger snapshot ring upgrade failed:', e);
+    return;
+  }
+
+  // Abort if the snapshot was replaced while we were fetching.
+  if (!trig.snapshot || trig.trigTime !== capturedTrigTime) return;
+
+  let updated = false;
+  Object.entries(ringSignals || {}).forEach(([key, sd]) => {
+    if (!sd || !sd.t || !sd.t.length) return;
+    trig.snapshot[key] = { t: Float64Array.from(sd.t), v: Float64Array.from(sd.v) };
+    updated = true;
+  });
+  if (updated) plots.forEach(p => { p.needsRedraw = true; });
 }
 function trigArm() {
   // Do NOT clear trig.snapshot here — keep the last waveform and trigger marker
@@ -431,6 +476,81 @@ function lttb(t, v, threshold) {
   return { t: outT, v: outV };
 }
 
+/* ════════════════════════════════════════════════════════════════
+   Hybrid zoom: hi-res data fetched from /api/zoom on demand
+   ════════════════════════════════════════════════════════════════ */
+function cancelZoomFetch() {
+  if (_zoomFetchTimer !== null) { clearTimeout(_zoomFetchTimer); _zoomFetchTimer = null; }
+}
+function scheduleZoomFetch(t0, t1) {
+  cancelZoomFetch();
+  _zoomFetchTimer = setTimeout(() => { _zoomFetchTimer = null; doZoomFetch(t0, t1); }, 150);
+}
+
+async function doZoomFetch(t0, t1) {
+  // Collect all signal keys across all plots; each key encodes sourceId as prefix.
+  const allKeys = new Set();
+  plots.forEach(p => p.traces.forEach(k => allKeys.add(k)));
+  if (allKeys.size === 0) return;
+
+  const targetPts = Math.max(400, (plots.find(p => p.uplot)?.uplot?.width || 600) * 2);
+  const url = `/api/zoom?t0=${t0}&t1=${t1}&n=${targetPts}&signals=${[...allKeys].join(',')}`;
+  let fetched;
+  try {
+    const resp = await fetch(url);
+    if (!resp.ok) return;
+    fetched = await resp.json();
+  } catch (e) { console.warn('zoom fetch:', e); return; }
+
+  const sigs = fetched && fetched.signals;
+  if (!sigs) return;
+
+  // Convert arrays from JSON to Float64Array and store per-plot.
+  const merged = {};
+  Object.entries(sigs).forEach(([k, sd]) => {
+    if (!sd || !sd.t || !sd.v) return;
+    merged[k] = { t: Float64Array.from(sd.t), v: Float64Array.from(sd.v) };
+  });
+
+  plots.forEach(p => {
+    // Only store if this plot's range still matches what we fetched.
+    if (!p.xRange || Math.abs(p.xRange[0] - t0) > 1e-9 || Math.abs(p.xRange[1] - t1) > 1e-9) return;
+    const plotSigs = {};
+    p.traces.forEach(k => { if (merged[k]) plotSigs[k] = merged[k]; });
+    if (Object.keys(plotSigs).length > 0) {
+      zoomData[p.id] = { signals: plotSigs, t0, t1 };
+      p.needsRedraw = true;
+    }
+  });
+}
+
+// Build uPlot data arrays from server-fetched hi-res signal data.
+function buildDataFromFetched(p, fetchedSignals, targetPts) {
+  let masterKey = p.traces[0], masterCount = -1, masterRate = -1;
+  for (const key of p.traces) {
+    const sd = fetchedSignals[key];
+    if (!sd || !sd.t || !sd.t.length) continue;
+    const rate = getKeySamplingRate(key);
+    if (rate > masterRate || (rate === masterRate && sd.t.length > masterCount)) {
+      masterRate = rate; masterCount = sd.t.length; masterKey = key;
+    }
+  }
+  const masterSd = fetchedSignals[masterKey];
+  if (!masterSd || !masterSd.t.length)
+    return [new Float64Array(0), ...p.traces.map(() => new Float64Array(0))];
+
+  const dec = lttb(masterSd.t, masterSd.v, targetPts);
+  const sharedT = dec.t;
+  const yArrays = [];
+  for (const key of p.traces) {
+    if (key === masterKey) { yArrays.push(dec.v); continue; }
+    const sd = fetchedSignals[key];
+    if (!sd || !sd.t.length) { yArrays.push(new Float64Array(sharedT.length)); continue; }
+    yArrays.push(resampleLinear(sd.t, sd.v, sharedT));
+  }
+  return [sharedT, ...yArrays];
+}
+
 /* ════════════════════════════════════════════════════════════════
    uPlot helpers
    ════════════════════════════════════════════════════════════════ */
@@ -903,6 +1023,14 @@ function buildLiveData(p) {
   // raises the effective sample cap and reveals full resolution.
   const targetPts = Math.max(LTTB_MIN, ((p.uplot ? p.uplot.width : p.div.clientWidth) || 600) * 2);
 
+  // When zoomed, prefer server-fetched hi-res data if it covers this exact range.
+  if (p.xRange) {
+    const zd = zoomData[p.id];
+    if (zd && Math.abs(zd.t0 - t0) < 1e-9 && Math.abs(zd.t1 - t1) < 1e-9) {
+      return buildDataFromFetched(p, zd.signals, targetPts);
+    }
+  }
+
   // Slice all traces once; pick the master time grid using configured samplingRate
   // as the primary criterion (unambiguous, independent of buffer fill / trace order).
   // Fall back to raw sample count for signals without a configured rate.
@@ -1019,6 +1147,9 @@ function onZoom(sourcePlotId, min, max) {
 
   // Mark all plots dirty (re-slice data to the new range for full resolution)
   plots.forEach(p => { p.needsRedraw = true; });
+
+  // Schedule hi-res fetch from ring buffers.
+  scheduleZoomFetch(min, max);
 }
 
 // Undo last zoom/pan action
@@ -1027,6 +1158,10 @@ function zoomBack() {
   const prev = zoomHistory.pop();
   if (!zoomHistory.length) document.getElementById('btn-zoom-back').style.display = 'none';
 
+  // Discard stale zoom data regardless of direction.
+  Object.keys(zoomData).forEach(k => delete zoomData[k]);
+  cancelZoomFetch();
+
   if (prev === null) {
     // Was at auto/rolling state before the zoom
     resetZoom();
@@ -1038,11 +1173,14 @@ function zoomBack() {
       p.needsRedraw = true;
     });
     zoomGuard = false;
+    scheduleZoomFetch(prev[0], prev[1]);
   }
 }
 
 // Reset to auto/rolling window (clears all zoom)
 function resetZoom() {
+  Object.keys(zoomData).forEach(k => delete zoomData[k]);
+  cancelZoomFetch();
   syncLocked = false;
   document.getElementById('btn-sync-resume').style.display = 'none';
   if (trig.enabled && trig.snapshot) {
@@ -1097,6 +1235,7 @@ function zoomFit() {
     p.needsRedraw = true;
   });
   zoomGuard = false;
+  scheduleZoomFetch(gMin, gMax);
 }
 
 // Auto = return to rolling window / full trigger window
@@ -1464,34 +1603,112 @@ function buildLayoutMenu() {
 }
 
 /* ════════════════════════════════════════════════════════════════
-   Export CSV (all plots)
+   Export CSV (all plots) — fetches full-resolution data from ring
    ════════════════════════════════════════════════════════════════ */
-function exportAllCSV() {
+async function exportAllCSV() {
+  const btn = document.getElementById('btn-csv-all');
+  if (btn.disabled) return;
+
   const inTrigMode = trig.enabled && trig.snapshot !== null;
-  // Collect unique signal keys across all plots (preserving order)
+
+  // Collect unique signal keys across all plots (preserving order).
   const keys = [];
   plots.forEach(p => p.traces.forEach(k => { if (!keys.includes(k)) keys.push(k); }));
   if (!keys.length) return;
 
+  // Determine time range to export.
+  let t0, t1, relOffset = 0;
+  if (inTrigMode) {
+    // Export the full trigger window around the trigger event.
+    t0 = trig.trigTime - trigPreSec();
+    t1 = trig.trigTime + trigPostSec();
+    relOffset = trig.trigTime;
+  } else {
+    // Use the current zoom range if active, else the rolling window.
+    const refPlot = plots.find(p => p.xRange);
+    if (refPlot) {
+      [t0, t1] = refPlot.xRange;
+    } else {
+      let plotNow = -Infinity;
+      keys.forEach(k => {
+        const buf = buffers[k];
+        if (buf && buf.size > 0) {
+          const t = buf.t[(buf.head - 1 + buf.cap) % buf.cap];
+          if (t > plotNow) plotNow = t;
+        }
+      });
+      if (!isFinite(plotNow)) plotNow = Date.now() / 1000;
+      t0 = plotNow - windowSec;
+      t1 = plotNow;
+    }
+  }
+
+  // Show loading state.
+  const origLabel = btn.textContent;
+  btn.textContent = '⏳ Downloading…';
+  btn.disabled = true;
+
+  // Fetch full-resolution ring data (n=0 → no LTTB decimation).
+  const url = `/api/zoom?t0=${t0}&t1=${t1}&n=0&signals=${keys.join(',')}`;
+  let ringSignals = null;
+  try {
+    const resp = await fetch(url);
+    if (resp.ok) {
+      const json = await resp.json();
+      ringSignals = json && json.signals;
+    }
+  } catch (e) {
+    console.warn('CSV export: ring fetch failed, falling back to push buffer', e);
+  } finally {
+    btn.textContent = origLabel;
+    btn.disabled = false;
+  }
+
+  // Build per-signal time/value arrays.
+  // Priority: ring buffer (full res) → trigger snapshot → push buffer.
   const slices = keys.map(key => {
+    const rd = ringSignals && ringSignals[key];
+    if (rd && rd.t && rd.t.length > 0) {
+      const t = rd.t, v = rd.v;
+      if (inTrigMode) {
+        return { t: Array.from(t).map(ts => ts - relOffset), v: Array.from(v) };
+      }
+      return { t: Array.from(t), v: Array.from(v) };
+    }
+    // Fallback: push buffer or trigger snapshot.
     if (inTrigMode) {
       const raw = trig.snapshot[key] || { t: new Float64Array(0), v: new Float64Array(0) };
-      return { t: Array.from(raw.t).map(ts => ts - trig.trigTime), v: Array.from(raw.v) };
+      return { t: Array.from(raw.t).map(ts => ts - relOffset), v: Array.from(raw.v) };
     }
     const buf = buffers[key]; if (!buf) return { t: [], v: [] };
-    const sl = getBufferSlice(buf);
+    const sl = getBufferSliceRange(buf, t0, t1);
     return { t: Array.from(sl.t), v: Array.from(sl.v) };
   });
 
-  const allT = new Set(); slices.forEach(s => s.t.forEach(t => allT.add(t)));
+  // Merge all timestamps and build aligned rows.
+  const allT = new Set();
+  slices.forEach(s => s.t.forEach(t => allT.add(t)));
   const sortedT = Array.from(allT).sort((a, b) => a - b);
-  const lookups = slices.map(s => { const m = new Map(); s.t.forEach((t, i) => m.set(t, s.v[i])); return m; });
-  const hdr = [(inTrigMode ? 'time_rel_s' : 'time_s'), ...keys].join(',');
-  const rows = sortedT.map(t => [t.toFixed(9), ...lookups.map(lk => lk.has(t) ? lk.get(t) : '')].join(','));
+  if (!sortedT.length) return;
+
+  const lookups = slices.map(s => {
+    const m = new Map();
+    s.t.forEach((t, i) => m.set(t, s.v[i]));
+    return m;
+  });
+
+  // Strip "sourceId:" prefix from column headers for readability.
+  const displayKeys = keys.map(k => (k.includes(':') ? k.split(':').slice(1).join(':') : k));
+  const hdr = [(inTrigMode ? 'time_rel_s' : 'time_s'), ...displayKeys].join(',');
+  const rows = sortedT.map(t =>
+    [t.toFixed(9), ...lookups.map(lk => (lk.has(t) ? lk.get(t) : ''))].join(',')
+  );
   const blob = new Blob([hdr + '\n' + rows.join('\n')], { type: 'text/csv' });
   const a = document.createElement('a');
-  a.href = URL.createObjectURL(blob); a.download = 'signals_' + Date.now() + '.csv';
-  a.click(); URL.revokeObjectURL(a.href);
+  a.href = URL.createObjectURL(blob);
+  a.download = 'signals_' + Date.now() + '.csv';
+  a.click();
+  URL.revokeObjectURL(a.href);
 }
 
 /* ════════════════════════════════════════════════════════════════