feat: Improve thermal display and build system

- Replace emoji thermal indicators with modern progress bar UI
- Switch temperature source to battery sensor for better accuracy
- Adjust temperature thresholds (30°C-45°C range)
- Add automatic Vulkan Validation Layer download for Android
- Downgrade Java/Kotlin target to 17 for wider compatibility

The thermal display now shows a visual progress bar with percentage
instead of emojis, making it easier to gauge system temperature at
a glance. Temperature reading now comes from the battery sensor
which is more reliable across devices.

Build system improvements include automated VVL binary downloads
and installation for Android builds when CITRON_DOWNLOAD_ANDROID_VVL
is enabled. Java target downgraded to 17 to ensure compatibility
with current Android toolchain.

CMakeLists.txt

@@ -97,7 +97,26 @@ if (ANDROID OR WIN32 OR APPLE)
 endif()
 option(ENABLE_OPENSSL "Enable OpenSSL backend for ISslConnection" ${DEFAULT_ENABLE_OPENSSL})
 
-# Copy the VVL arm64 binary to src/android/app/main/jniLibs. REF: https://github.com/KhronosGroup/Vulkan-ValidationLayers/actions/workflows/vvl.yml
+if (ANDROID AND CITRON_DOWNLOAD_ANDROID_VVL)
+    set(vvl_version "sdk-1.3.261.1")
+    set(vvl_zip_file "${CMAKE_BINARY_DIR}/externals/vvl-android.zip")
+    if (NOT EXISTS "${vvl_zip_file}")
+        # Download and extract validation layer release to externals directory
+        set(vvl_base_url "https://github.com/KhronosGroup/Vulkan-ValidationLayers/releases/download")
+        file(DOWNLOAD "${vvl_base_url}/${vvl_version}/android-binaries-${vvl_version}-android.zip"
+            "${vvl_zip_file}" SHOW_PROGRESS)
+        execute_process(COMMAND ${CMAKE_COMMAND} -E tar xf "${vvl_zip_file}"
+                        WORKING_DIRECTORY "${CMAKE_BINARY_DIR}/externals")
+    endif()
+
+    # Copy the arm64 binary to src/android/app/main/jniLibs only if it doesn't exist
+    set(vvl_lib_path "${CMAKE_CURRENT_SOURCE_DIR}/src/android/app/src/main/jniLibs/arm64-v8a/")
+    set(vvl_lib_file "${vvl_lib_path}/libVkLayer_khronos_validation.so")
+    if (NOT EXISTS "${vvl_lib_file}")
+        file(COPY "${CMAKE_BINARY_DIR}/externals/android-binaries-${vvl_version}/arm64-v8a/libVkLayer_khronos_validation.so"
+                DESTINATION "${vvl_lib_path}")
+    endif()
+endif()
 
 if (ANDROID)
     set(CMAKE_SKIP_INSTALL_RULES ON)

src/android/app/build.gradle.kts

@@ -35,12 +35,12 @@ android {
     }
 
     compileOptions {
-        sourceCompatibility = JavaVersion.VERSION_21
+        sourceCompatibility = JavaVersion.VERSION_17
-        targetCompatibility = JavaVersion.VERSION_21
+        targetCompatibility = JavaVersion.VERSION_17
     }
 
     kotlinOptions {
-        jvmTarget = "21"
+        jvmTarget = "17"
     }
 
     packaging {

src/android/app/src/main/java/org/citron/citron_emu/fragments/EmulationFragment.kt

@@ -532,20 +532,20 @@ class EmulationFragment : Fragment(), SurfaceHolder.Callback {
                     !emulationViewModel.isEmulationStopping.value
                 ) {
                     val thermalStatus = when (powerManager.currentThermalStatus) {
-                        PowerManager.THERMAL_STATUS_LIGHT -> "😥"
+                        PowerManager.THERMAL_STATUS_LIGHT -> 0.25f
-                        PowerManager.THERMAL_STATUS_MODERATE -> "🥵"
+                        PowerManager.THERMAL_STATUS_MODERATE -> 0.5f
-                        PowerManager.THERMAL_STATUS_SEVERE -> "🔥"
+                        PowerManager.THERMAL_STATUS_SEVERE -> 0.75f
                         PowerManager.THERMAL_STATUS_CRITICAL,
                         PowerManager.THERMAL_STATUS_EMERGENCY,
-                        PowerManager.THERMAL_STATUS_SHUTDOWN -> "☢️"
+                        PowerManager.THERMAL_STATUS_SHUTDOWN -> 1.0f
-                        else -> "🙂"
+                        else -> 0f
                     }
 
-                    // Get temperature in Celsius from thermal sensor
+                    // Get temperature from battery thermal sensor
                     val temperature = try {
-                        val process = Runtime.getRuntime().exec("cat /sys/class/thermal/thermal_zone0/temp")
+                        val process = Runtime.getRuntime().exec("cat /sys/class/power_supply/battery/temp")
                         val reader = process.inputStream.bufferedReader()
-                        val temp = reader.readLine().toFloat() / 1000f // Convert from millicelsius to celsius
+                        val temp = reader.readLine().toFloat() / 10f // Convert from decidegrees to degrees
                         reader.close()
                         temp
                     } catch (e: Exception) {
@@ -556,16 +556,30 @@ class EmulationFragment : Fragment(), SurfaceHolder.Callback {
                     val fahrenheit = (temperature * 9f / 5f) + 32f
 
                     if (_binding != null) {
-                        // Color interpolation based on temperature (green at 45°C, red at 85°C)
+                        // Color interpolation based on temperature (green at 30°C, red at 45°C)
-                        val normalizedTemp = ((temperature - 45f) / 40f).coerceIn(0f, 1f)
+                        val normalizedTemp = ((temperature - 30f) / 15f).coerceIn(0f, 1f)
                         val red = (normalizedTemp * 255).toInt()
                         val green = ((1f - normalizedTemp) * 255).toInt()
                         val color = android.graphics.Color.rgb(red, green, 0)
 
+                        // Create a modern progress bar using block elements
+                        val progressBarLength = 12
+                        val filledBars = (thermalStatus * progressBarLength).toInt()
+                        val progressBar = buildString {
+                            append("│") // Left border
+                            repeat(filledBars) { append("█") }
+                            repeat(progressBarLength - filledBars) { append("░") }
+                            append("│") // Right border
+
+                            // Add percentage
+                            append(" ")
+                            append(String.format("%3d%%", (thermalStatus * 100).toInt()))
+                        }
+
                         binding.showThermalsText.setTextColor(color)
                         binding.showThermalsText.text = String.format(
-                            "%s %.1f°C\n%.1f°F",
+                            "%s\n%.1f°C • %.1f°F",
-                            thermalStatus,
+                            progressBar,
                             temperature,
                             fahrenheit
                         )