Initial commit for first version of project

GasTankAR/Views/TankAR/TankDepthFadeMaterial.swift

@@ -0,0 +1,63 @@
+//
+//  TankDepthFadeMaterial.swift
+//  GasTankAR
+//
+//  Created by Dennis Nemec on 26.08.26.
+//
+
+import RealityKit
+import Metal
+
+/// Kapselt das Höhen-Fade-CustomMaterial für den unterirdischen Tank:
+/// verblasst die Opacity anhand der Welt-Höhe (Kopf opak, vergrabener Teil transparent).
+@MainActor
+enum TankDepthFadeMaterial {
+    /// Fade-Band (Meter) unterhalb der Bodenkante, über das die Transparenz einsetzt.
+    static let band: Float = 0.15
+    /// Minimale Opacity des vergrabenen Teils.
+    static let belowAlpha: Float = 0.3
+
+    private static let shader: CustomMaterial.SurfaceShader? = {
+        guard let library = MTLCreateSystemDefaultDevice()?.makeDefaultLibrary() else { return nil }
+        return CustomMaterial.SurfaceShader(named: "tankDepthFadeSurface", in: library)
+    }()
+
+    /// Ersetzt die Materialien der Entity (rekursiv) durch das Fade-CustomMaterial.
+    static func apply(to entity: Entity) {
+        guard let shader else { return }
+        forEachModelEntity(entity) { modelEntity in
+            guard var component = modelEntity.model else { return }
+            component.materials = component.materials.map { material in
+                guard var custom = try? CustomMaterial(from: material, surfaceShader: shader) else {
+                    return material
+                }
+                custom.blending = .transparent(opacity: 1.0)
+                custom.custom.value = SIMD4<Float>(0, band, belowAlpha, 0)
+                return custom
+            }
+            modelEntity.model = component
+        }
+    }
+
+    /// Aktualisiert die Boden-Höhe (Welt-Y) in bereits angewandten Fade-Materialien.
+    static func updateGroundY(_ groundY: Float, on entity: Entity) {
+        forEachModelEntity(entity) { modelEntity in
+            guard var component = modelEntity.model else { return }
+            component.materials = component.materials.map { material in
+                guard var custom = material as? CustomMaterial else { return material }
+                custom.custom.value = SIMD4<Float>(groundY, band, belowAlpha, 0)
+                return custom
+            }
+            modelEntity.model = component
+        }
+    }
+
+    private static func forEachModelEntity(_ entity: Entity, _ body: (ModelEntity) -> Void) {
+        if let modelEntity = entity as? ModelEntity {
+            body(modelEntity)
+        }
+        for child in entity.children {
+            forEachModelEntity(child, body)
+        }
+    }
+}