add spot constructor

thermion_dart/lib/thermion_dart/viewer/shared_types/light_options.dart

@@ -38,6 +38,7 @@ class DirectLight {
     this.sunHaloSize = 10.0,
     this.sunHaloFallof = 80.0,
   });
+
   DirectLight.point({
     double color = 6500,
     double intensity = 100000,
@@ -73,4 +74,25 @@ DirectLight.sun({
     sunHaloSize: sunHaloSize,
     sunHaloFallof: sunHaloFalloff,
   );
+
+  DirectLight.spot({
+    double color = 6500,
+    double intensity = 100000,
+    bool castShadows = true,
+    Vector3? position,
+    Vector3? direction,
+    double falloffRadius = 1.0,
+    double spotLightConeInner = pi / 8,
+    double spotLightConeOuter = pi / 4,
+  }) : this(
+    type: LightType.SPOT,
+    color: color,
+    intensity: intensity,
+    castShadows: castShadows,
+    position: position ?? Vector3(0, 1, 0),
+    direction: direction ?? Vector3(0, -1, 0),
+    falloffRadius: falloffRadius,
+    spotLightConeInner: spotLightConeInner,
+    spotLightConeOuter: spotLightConeOuter,
+  );
 }