fix(simulator): sample LCD at a fixed cadence so the final frame is always painted (#7504)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

companion/src/simulation/widgets/lcdwidget.cpp

@@ -71,14 +71,26 @@ void LcdWidget::makeScreenshot(const QString &fileName)
 
 void LcdWidget::onLcdChanged(uint8_t* lcdBuf, bool light)
 {
+  // Ingest only: store the latest frame and let frameTimer drive the repaint.
+  // Sampling on a fixed cadence caps the repaint rate without dropping the
+  // final frame of a burst, regardless of how frames are delivered.
   QMutexLocker locker(&lcdMtx);
   lightEnable = light;
   if (lcdBuf) memcpy(localBuf, lcdBuf, lcdSize);
-  if (!redrawTimer.isValid() ||
-      redrawTimer.hasExpired(LCD_WIDGET_REFRESH_PERIOD)) {
-    update();
-    redrawTimer.start();
+  dirty = true;
+  if (!frameTimer.isActive())
+    frameTimer.start();
+}
+
+void LcdWidget::onFrameTick()
+{
+  QMutexLocker locker(&lcdMtx);
+  if (!dirty) {  // idle: stop until the next frame arrives
+    frameTimer.stop();
+    return;
   }
+  dirty = false;
+  update();
 }
 
 void LcdWidget::doPaint(QPainter &p)

companion/src/simulation/widgets/lcdwidget.h

@@ -26,15 +26,16 @@
 #include <QPainter>
 #include <QClipboard>
 #include <QDir>
-#include <QElapsedTimer>
 #include <QMutex>
 #include <QMutexLocker>
 #include <QMouseEvent>
+#include <QTimer>
 #include <AppDebugMessageHandler>
 
 #include "appdata.h"
 
-#define LCD_WIDGET_REFRESH_PERIOD    16  // [ms] 16 = 62.5fps
+#define LCD_WIDGET_REFRESH_PERIOD    10  // [ms] 10 = 100fps cap (color is
+                                         // firmware-limited to ~20fps anyway)
 
 class LcdWidget : public QWidget
 {
@@ -50,6 +51,8 @@ class LcdWidget : public QWidget
       bgDefaultColor(QColor(148, 156, 149)),
       fgDefaultColor(QColor(0, 0, 0))
   {
+    frameTimer.setInterval(LCD_WIDGET_REFRESH_PERIOD);
+    connect(&frameTimer, &QTimer::timeout, this, &LcdWidget::onFrameTick);
   }
 
   ~LcdWidget()
@@ -84,8 +87,10 @@ class LcdWidget : public QWidget
   QColor bgDefaultColor;
   QColor fgDefaultColor;
   QMutex lcdMtx;
-  QElapsedTimer redrawTimer;
+  QTimer frameTimer;
+  bool dirty = false;
 
+  void onFrameTick();
   void doPaint(QPainter &p);
 
   void paintEvent(QPaintEvent *) override;