feat: add BillboardNode, TextNode, PhysicsNode + 3 new samples

samples/physics-demo/build.gradle

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+plugins {
+    id 'com.android.application'
+    id 'org.jetbrains.kotlin.android'
+    id 'org.jetbrains.kotlin.plugin.compose'
+}
+
+android {
+    namespace "io.github.sceneview.sample.physicsdemo"
+
+    compileSdk 36
+
+    defaultConfig {
+        applicationId "io.github.sceneview.sample.physicsdemo"
+        minSdk 28
+        targetSdk 36
+        versionCode 1
+        versionName "1.0.0"
+    }
+
+    buildTypes {
+        release {
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17
+    }
+    buildFeatures {
+        compose true
+    }
+    androidResources {
+        noCompress 'filamat', 'ktx'
+    }
+}
+
+dependencies {
+    implementation project(":samples:common")
+
+    implementation "androidx.compose.ui:ui:1.10.5"
+    implementation "androidx.compose.foundation:foundation:1.10.5"
+    implementation 'androidx.activity:activity-compose:1.10.1'
+    implementation 'androidx.compose.material:material:1.10.5'
+    implementation "androidx.compose.ui:ui-tooling-preview:1.10.5"
+    debugImplementation "androidx.compose.ui:ui-tooling:1.10.5"
+
+    // SceneView
+    implementation project(":sceneview")
+}

samples/physics-demo/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <application
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:theme="@style/Theme.SceneViewSample">
+        <activity
+            android:name=".MainActivity"
+            android:configChanges="orientation|screenSize"
+            android:exported="true"
+            android:label="@string/app_name"
+            android:screenOrientation="locked">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

samples/physics-demo/src/main/java/io/github/sceneview/sample/physicsdemo/MainActivity.kt

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+package io.github.sceneview.sample.physicsdemo
+
+import android.os.Bundle
+import android.view.MotionEvent
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.navigationBarsPadding
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.material3.TopAppBar
+import androidx.compose.material3.TopAppBarDefaults
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateListOf
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import io.github.sceneview.Scene
+import io.github.sceneview.math.Position
+import io.github.sceneview.math.Size
+import io.github.sceneview.node.PhysicsNode
+import io.github.sceneview.node.SphereNode
+import io.github.sceneview.rememberCameraNode
+import io.github.sceneview.rememberEngine
+import io.github.sceneview.rememberEnvironment
+import io.github.sceneview.rememberEnvironmentLoader
+import io.github.sceneview.rememberMainLightNode
+import io.github.sceneview.rememberMaterialLoader
+import io.github.sceneview.rememberModelLoader
+import io.github.sceneview.rememberOnGestureListener
+import io.github.sceneview.sample.SceneviewTheme
+
+/**
+ * Physics Demo — tap anywhere to throw a ball that falls and bounces off the floor.
+ *
+ * - The floor is a flat CubeNode (thick slab at y = 0).
+ * - Each tap spawns a SphereNode at y = 2.5 m above the floor with a small random
+ *   horizontal impulse so balls spread out.
+ * - Each sphere is driven by a pure-Kotlin PhysicsBody (Euler integration, 9.8 m/s² gravity,
+ *   configurable restitution).
+ * - Old balls (beyond MAX_BALLS) are removed from the list so the scene stays light.
+ */
+class MainActivity : ComponentActivity() {
+
+    @OptIn(ExperimentalMaterial3Api::class)
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+
+        setContent {
+            SceneviewTheme {
+                Box(modifier = Modifier.fillMaxSize()) {
+
+                    val engine = rememberEngine()
+                    val modelLoader = rememberModelLoader(engine)
+                    val materialLoader = rememberMaterialLoader(engine)
+                    val environmentLoader = rememberEnvironmentLoader(engine)
+                    val environment = rememberEnvironment(environmentLoader)
+
+                    // Camera sits slightly above and behind the scene, looking at the origin.
+                    val cameraNode = rememberCameraNode(engine) {
+                        position = Position(x = 0f, y = 1.5f, z = 4f)
+                        lookAt(Position(0f, 0.5f, 0f))
+                    }
+
+                    val mainLightNode = rememberMainLightNode(engine) {
+                        intensity = 100_000f
+                    }
+
+                    // ── Physics state ─────────────────────────────────────────────────────────
+
+                    /**
+                     * Each entry is a SphereNode whose position will be driven by a PhysicsBody.
+                     * We store the node directly in a SnapshotStateList so that recomposition
+                     * is triggered when balls are added/removed.
+                     */
+                    val balls = remember { mutableStateListOf<SphereNode>() }
+
+                    // Counter for giving each ball a slightly different horizontal velocity.
+                    var ballCount by remember { mutableStateOf(0) }
+
+                    // ── Scene ─────────────────────────────────────────────────────────────────
+
+                    Scene(
+                        modifier = Modifier.fillMaxSize(),
+                        engine = engine,
+                        modelLoader = modelLoader,
+                        cameraNode = cameraNode,
+                        environment = environment,
+                        mainLightNode = mainLightNode,
+                        onGestureListener = rememberOnGestureListener(
+                            onSingleTapConfirmed = { event, _ ->
+                                // Spawn a new ball at every tap.
+                                val index = ballCount++
+
+                                // Alternate horizontal direction so balls spread left/right.
+                                val sign = if (index % 2 == 0) 1f else -1f
+                                val lateralSpeed = 0.3f + (index % 5) * 0.15f
+
+                                val ball = SphereNode(
+                                    engine = engine,
+                                    radius = BALL_RADIUS,
+                                    materialInstance = null
+                                ).apply {
+                                    position = Position(
+                                        x = sign * lateralSpeed * 0.5f,
+                                        y = SPAWN_HEIGHT,
+                                        z = 0f
+                                    )
+                                }
+                                balls.add(ball)
+
+                                // Keep the scene lean: drop the oldest ball once we hit the cap.
+                                if (balls.size > MAX_BALLS) {
+                                    balls.removeAt(0)
+                                }
+                                true
+                            }
+                        )
+                    ) {
+                        // ── Floor slab ────────────────────────────────────────────────────────
+                        // A thin box centred at y = -FLOOR_HALF_THICKNESS.
+                        // The top surface is at y = 0 — matching PhysicsBody.floorY default.
+                        CubeNode(
+                            size = Size(FLOOR_WIDTH, FLOOR_THICKNESS, FLOOR_DEPTH),
+                            position = Position(y = -FLOOR_HALF_THICKNESS),
+                            materialInstance = null
+                        )
+
+                        // ── Balls ─────────────────────────────────────────────────────────────
+                        for ((idx, ball) in balls.withIndex()) {
+                            // Alternate horizontal launch velocity per ball.
+                            val sign = if (idx % 2 == 0) 1f else -1f
+                            val lateralSpeed = 0.3f + (idx % 5) * 0.15f
+
+                            // Attach the ball node into the scene.
+                            Node(apply = { addChildNode(ball) })
+
+                            // Drive it with physics.
+                            PhysicsNode(
+                                node = ball,
+                                mass = 1f,
+                                restitution = RESTITUTION,
+                                linearVelocity = Position(
+                                    x = sign * lateralSpeed,
+                                    y = 0f,
+                                    z = 0f
+                                ),
+                                floorY = 0f,
+                                radius = BALL_RADIUS
+                            )
+                        }
+                    }
+
+                    // ── UI overlay ────────────────────────────────────────────────────────────
+
+                    TopAppBar(
+                        title = { Text(text = stringResource(id = R.string.app_name)) },
+                        colors = TopAppBarDefaults.topAppBarColors(
+                            containerColor = MaterialTheme.colorScheme.primary.copy(alpha = 0.25f),
+                            titleContentColor = MaterialTheme.colorScheme.onPrimary
+                        )
+                    )
+
+                    Text(
+                        modifier = Modifier
+                            .align(Alignment.BottomCenter)
+                            .navigationBarsPadding()
+                            .padding(bottom = 24.dp),
+                        text = "Tap anywhere to throw a ball",
+                        fontSize = 14.sp,
+                        color = MaterialTheme.colorScheme.onSurface.copy(alpha = 0.8f)
+                    )
+                }
+            }
+        }
+    }
+
+    companion object {
+        /** Maximum simultaneous balls in the scene. */
+        const val MAX_BALLS = 10
+
+        /** World-space Y at which new balls spawn. */
+        const val SPAWN_HEIGHT = 2.5f
+
+        /** Radius of each physics ball, metres. */
+        const val BALL_RADIUS = 0.15f
+
+        /** Bounciness: 0 = dead stop, 1 = perfect bounce. */
+        const val RESTITUTION = 0.65f
+
+        // Floor geometry
+        const val FLOOR_WIDTH = 6f
+        const val FLOOR_DEPTH = 6f
+        const val FLOOR_THICKNESS = 0.1f
+        const val FLOOR_HALF_THICKNESS = FLOOR_THICKNESS / 2f
+    }
+}

samples/physics-demo/src/main/res/values/strings.xml

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+<resources>
+    <string name="app_name">Physics Demo</string>
+</resources>

samples/post-processing/build.gradle

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+plugins {
+    id 'com.android.application'
+    id 'org.jetbrains.kotlin.android'
+    id 'org.jetbrains.kotlin.plugin.compose'
+}
+
+android {
+    namespace 'io.github.sceneview.sample.postprocessing'
+
+    compileSdk 36
+
+    defaultConfig {
+        applicationId "io.github.sceneview.sample.postprocessing"
+        minSdk 28
+        targetSdk 36
+        versionCode 1
+        versionName "1.0.0"
+    }
+
+    buildTypes {
+        release {
+        }
+    }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_17
+        targetCompatibility JavaVersion.VERSION_17
+    }
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17
+    }
+    buildFeatures {
+        compose true
+    }
+    androidResources {
+        noCompress 'filamat', 'ktx'
+    }
+}
+
+dependencies {
+    implementation project(":samples:common")
+
+    implementation "androidx.compose.ui:ui:1.10.5"
+    implementation "androidx.compose.foundation:foundation:1.10.5"
+    implementation 'androidx.activity:activity-compose:1.10.1'
+    implementation 'androidx.compose.material:material:1.10.5'
+    implementation 'androidx.compose.material:material-icons-extended:1.7.8'
+    implementation "androidx.compose.ui:ui-tooling-preview:1.10.5"
+    debugImplementation "androidx.compose.ui:ui-tooling:1.10.5"
+
+    // SceneView
+    implementation project(":sceneview")
+}

samples/post-processing/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <application
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:theme="@style/Theme.SceneViewSample">
+        <activity
+            android:name=".MainActivity"
+            android:configChanges="orientation|screenSize"
+            android:exported="true"
+            android:label="@string/app_name"
+            android:screenOrientation="locked">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+</manifest>

samples/post-processing/src/main/assets

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+../../../model-viewer/src/main/assets