Allow 0% battery level

gui/src/components/tracker/TrackerBattery.tsx

@@ -13,7 +13,9 @@ export function TrackerBattery({
   textColor = 'primary',
 }: {
   /**
-   * a [0, 1] value range is expected
+   * Normally [0, 1] value range
+   * Values >1 indicate fully charged
+   * Values <0 also indicate 0%
    */
   value: number;
   voltage?: number | null;
@@ -36,11 +38,13 @@ export function TrackerBattery({
   const debug = config?.debug || config?.devSettings.moreInfo;
   const showVoltage = moreInfo && voltage && debug;
 
+  const pct = Math.min(Math.max(value, 0), 1);
+
   return (
     <Tooltip
       disabled={charging || !runtime || debug}
       preferedDirection="left"
-      content=<Typography>{percentFormatter.format(value)}</Typography>
+      content=<Typography>{percentFormatter.format(pct)}</Typography>
     >
       <div className="flex gap-2">
         <div className="flex flex-col justify-around">
@@ -61,7 +65,7 @@ export function TrackerBattery({
             )}
             {!charging && (!runtime || debug) && (
               <Typography color={textColor}>
-                {percentFormatter.format(value)}
+                {percentFormatter.format(pct)}
               </Typography>
             )}
             {showVoltage && (

server/core/src/main/java/dev/slimevr/tracking/trackers/hid/HIDCommon.kt

@@ -268,9 +268,9 @@ class HIDCommon {
 			}
 			// -1: Not known (e.g. not yet calculated after wake up, reusing known value is okay), 0: N/A (e.g. charging)
 			if (batt != null) {
-				tracker.batteryLevel = if (batt == 128) 1f else (batt and 127).toFloat()
+				tracker.batteryLevel = if (batt == 128) -1f else (batt and 127).toFloat()
 			}
-			// Server still won't display battery at 0% at all
+			// Server displays 0% if received 255 or -1, otherwise 0 will hide battery icon
 			if (batt_v != null) {
 				tracker.batteryVoltage = (batt_v.toFloat() + 245f) / 100f
 			}

server/core/src/main/java/dev/slimevr/tracking/trackers/udp/TrackersUDPServer.kt

@@ -485,7 +485,18 @@ class TrackersUDPServer(private val port: Int, name: String, private val tracker
 
 			is UDPPacket12BatteryLevel -> connection?.trackers?.values?.forEach {
 				it.batteryVoltage = packet.voltage
-				it.batteryLevel = packet.level * 100
+				// Firmware does not verify the voltage level at all
+				// Instead guess if a battery is present or not
+				// Too low or high voltage should mean there is no battery or there is a measurement error
+				// Some ESP can run at 2.3V, set a limit at 2V
+				// Below this the tracker is definitely dead if everything is working properly
+				if (it.batteryVoltage > 2f && it.batteryVoltage < 6f) {
+					// Assuming floor when converting to int
+					it.batteryLevel = if (packet.level < 0.01f) -1f else packet.level * 100
+				} else {
+					it.batteryLevel = 0f
+				}
+				// Server displays 0% if received 255 or -1, otherwise 0 will hide battery icon
 			}
 
 			is UDPPacket13Tap -> {