Issue #411 - Adding pause button compatibility in imager service

[babo989]

Acquisition Pause/Resume Feature

Branch (Python): Feature-Pause
Dashboard Branch (Node-RED): Feature-Pause
Date: 2026-03-30

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Summary

Adds the ability to pause and resume an active acquisition. Pause takes effect between frames — it will not interrupt a pump mid-flow or a capture mid-save, keeping the acquisition state clean and resumable.

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Python Changes

controller/imager/stopflow.py — Core pause logic

New state: Added _paused threading.Event to Routine.__init__().

Modified run_step() — Added a blocking loop at the top of each step (after completion/interruption checks, before the pump runs):

# Block while paused, checking for interruption every second
while self._paused.is_set():
    if self._interrupted.wait(timeout=1.0):
        loguru.logger.info("Image acquisition was interrupted while paused!")
        return None

This means:

• Pause only takes effect between frames (after the current frame completes)
• While paused, the routine checks for stop/interrupt every 1 second
• Stopping while paused works immediately (within 1s)

New methods:

def pause(self) -> None:
    """Pause the routine between steps."""
    self._paused.set()

def resume(self) -> None:
    """Resume the routine after being paused."""
    self._paused.clear()

New property:

@property
def paused(self) -> bool:
    """Check whether the routine is currently paused."""
    return self._paused.is_set()

controller/imager/main.py — MQTT integration

Imager._handle_new_message() — Added two new action handlers:

elif action == "pause" and self._active_routine is not None:
    self._active_routine.pause()
elif action == "resume" and self._active_routine is not None:
    self._active_routine.resume()

ImageAcquisitionRoutine — Added pause() and resume() methods that delegate to the routine and publish MQTT status:

def pause(self) -> None:
    self._routine.pause()
    self._mqtt_client.publish("status/imager", '{"status":"Paused"}')

def resume(self) -> None:
    self._routine.resume()
    self._mqtt_client.publish("status/imager", '{"status":"Resumed"}')

---

Node-RED Changes

All changes are in flows.json on the Acquisition tab (71ede8b7dd88d90e).

UI Template (body node — 79bccc0355eb5d87)

New data property:

• acq_paused: false

New button (below Start/Stop, visible only during acquisition):

<v-row v-if="acq_status === 'on'" class="align-center pa-0">
  <v-col cols="12" class="pa-0">
    <v-btn block :color="acq_paused ? 'green' : 'orange'" variant="outlined"
      class="mt-2" style="height: 48px" @click="handlePauseToggle">
      {{ acq_paused ? 'Resume Acquisition' : 'Pause Acquisition' }}
    </v-btn>
  </v-col>
</v-row>

New method:

handlePauseToggle() {
  this.acq_paused = !this.acq_paused;
  if (typeof this.send !== "function") return;
  this.send({
    topic: "pause_control",
    payload: { action: this.acq_paused ? "pause" : "resume" }
  });
  this.acq_status_message = this.acq_paused ? "Paused" : "Resumed";
},

Updated computed properties:

• formattedStatus: "Paused" → "Acquisition paused. You may adjust settings.", "Resumed" → "Acquisition resumed."
• statusColor: "Paused" → orange, "Resumed" → green

Updated status watcher:

• Sets acq_paused = true on "paused" status, false on "resumed"
• Resets acq_paused = false when acquisition ends (done/stopped/error)

New Flow Nodes

Node	ID	Type	Purpose
pause?	a1b2c3d4e5f60001	switch	Routes pause_control topic separately from normal acq messages
pause/resume	a1b2c3d4e5f60002	function	Sets msg.topic = "imager/image" for MQTT publish

Message Routing

body → pageleave filter → pageview filter → pause? switch
  ├─ topic="pause_control" → pause/resume func → MQTT out (imager/image)
  └─ else → acq_status switch → (stop / start paths, unchanged)

---

MQTT API

New Actions

Topic	Payload	Effect
imager/image	{"action": "pause"}	Pauses acquisition between frames
imager/image	{"action": "resume"}	Resumes paused acquisition

New Status Messages

Topic	Payload	When
status/imager	{"status": "Paused"}	After pause takes effect
status/imager	{"status": "Resumed"}	After resume

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Behavior

• Pause button appears only when acquisition is running (acq_status === 'on')
• Button toggles between orange "Pause Acquisition" and green "Resume Acquisition"
• Pause takes effect after the current frame completes (pump + stabilize + capture)
• Stopping while paused works — the interrupt check runs every 1 second
• When acquisition ends (done/stopped/error), pause state resets automatically
• No changes to existing start/stop flow, MQTT topics, or pump/camera control

[sonnyp]

This was already merged in #929