Add VICE C64 emulator integration to Android companion app

Cross-compiles VICE 3.8 headless for ARM64 and x86_64 as part of the
  Android Studio build (Gradle buildVice task + build_vice.sh). The JNI
  bridge (vice_jni.c) renders frames into a shared framebuffer read by
  C64DisplayView, and forwards key events from C64KeyboardView to VICE's
  keyboard matrix. Without ROM files the app shows a placeholder blue
  screen; with ROMs and a .d64 disk image the full C64 emulator runs.

SchwertUndMagieOnPebbleCompanionApp/app/build.gradle.kts

@@ -1,3 +1,5 @@
+import java.util.Properties
+
 plugins {
     alias(libs.plugins.android.application)
 }
@@ -10,6 +12,8 @@ android {
         }
     }
 
+    ndkVersion = "30.0.14904198"
+
     defaultConfig {
         applicationId = "de.ladkau.schwertundmagieonpebblecompanionapp"
         minSdk = 24
@@ -18,6 +22,17 @@ android {
         versionName = "1.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+
+        ndk {
+            abiFilters += listOf("arm64-v8a", "x86_64")
+        }
+        externalNativeBuild {
+            cmake {
+                arguments("-DANDROID_STL=c++_shared")
+                // HAVE_VICE_SRC is detected automatically by CMakeLists.txt
+                // based on whether vice-libs/<abi>/libvice.a exists.
+            }
+        }
     }
 
     buildTypes {
@@ -33,6 +48,86 @@ android {
         sourceCompatibility = JavaVersion.VERSION_11
         targetCompatibility = JavaVersion.VERSION_11
     }
+    externalNativeBuild {
+        cmake {
+            path = file("src/main/jni/CMakeLists.txt")
+            version = "3.22.1"
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// VICE cross-compilation task
+//
+// Runs automatically before any CMake build step.
+// Skipped entirely if vice-libs/<abi>/libvice.a already exists.
+// The tarball at <project>/res/vice-3.8.tar.gz is unpacked by build_vice.sh.
+// ---------------------------------------------------------------------------
+
+val viceLibArm   = layout.projectDirectory.file("src/main/jni/vice-libs/arm64-v8a/libvice.a")
+val viceLibX86   = layout.projectDirectory.file("src/main/jni/vice-libs/x86_64/libvice.a")
+val viceTarball  = layout.projectDirectory.file("../res/vice-3.8.tar.gz")
+
+tasks.register("buildVice") {
+    group = "build"
+    description = "Cross-compile VICE 3.8 headless for Android (ARM64 + x86_64)"
+
+    inputs.file(viceTarball)
+    outputs.file(viceLibArm)
+    outputs.file(viceLibX86)
+
+    doLast {
+        if (viceLibArm.asFile.exists() && viceLibX86.asFile.exists()) {
+            logger.lifecycle("VICE already built — skipping")
+            return@doLast
+        }
+
+        val localProps = Properties().apply {
+            rootProject.file("local.properties").takeIf { it.exists() }
+                ?.reader()?.use { load(it) }
+        }
+        val sdkDir = localProps.getProperty("sdk.dir")
+            ?: System.getenv("ANDROID_HOME")
+            ?: ""
+        val ndkPath = localProps.getProperty("ndk.dir")
+            ?: System.getenv("ANDROID_NDK_HOME")
+            ?: System.getenv("ANDROID_NDK_ROOT")
+            ?: System.getenv("NDK")
+            ?: sdkDir.takeIf { it.isNotEmpty() }?.let { sdk ->
+                // NDK side-by-side: pick the first installed version
+                file("$sdk/ndk").takeIf { it.isDirectory }
+                    ?.listFiles()?.sorted()?.lastOrNull()?.absolutePath
+                    ?: "$sdk/ndk-bundle".takeIf { file("$sdk/ndk-bundle").isDirectory }
+            }
+            ?: throw GradleException(
+                "Android NDK not found.\n" +
+                "Install via: Android Studio → SDK Manager → SDK Tools → NDK (Side by side)"
+            )
+        logger.lifecycle("Building VICE with NDK at $ndkPath …")
+
+        val proc = ProcessBuilder("bash", "build_vice.sh")
+            .directory(layout.projectDirectory.dir("src/main/jni").asFile)
+            .redirectErrorStream(true)
+            .also { it.environment()["NDK"] = ndkPath }
+            .start()
+        proc.inputStream.bufferedReader().forEachLine { logger.lifecycle(it) }
+        val exit = proc.waitFor()
+        if (exit != 0) throw GradleException("build_vice.sh failed (exit $exit)")
+
+        // Touch CMakeLists.txt so CMake re-evaluates the EXISTS check on the
+        // next build and picks up the newly created libvice.a.
+        layout.projectDirectory.file("src/main/jni/CMakeLists.txt")
+            .asFile.setLastModified(System.currentTimeMillis())
+        logger.lifecycle("VICE build complete — CMakeLists.txt touched for re-evaluation")
+    }
+}
+
+// Run buildVice before any CMake configure or build step.
+tasks.whenTaskAdded {
+    if (name.startsWith("configureCMake") || name.startsWith("buildCMake") ||
+        name.startsWith("externalNativeBuild")) {
+        dependsOn("buildVice")
+    }
 }
 
 dependencies {