diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/GroundType.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/GroundType.kt
new file mode 100644
index 0000000..6cdc6f6
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/data/action/GroundType.kt
@@ -0,0 +1,53 @@
+@file:OptIn(ExperimentalSerializationApi::class, RDKTInternalAPI::class)
+
+package cn.rdlevel.rdkt.core.data.action
+
+import cn.rdlevel.rdkt.core.annotations.RDKTInternalAPI
+import cn.rdlevel.rdkt.core.data.ColorWithAlpha
+import cn.rdlevel.rdkt.core.data.WHITE
+import cn.rdlevel.rdkt.core.serialization.Flatten
+import cn.rdlevel.rdkt.core.serialization.flatten
+import kotlinx.serialization.*
+import kotlinx.serialization.json.JsonClassDiscriminator
+
+/**
+ * Represents the type and the settings of the background.
+ */
+@Serializable
+@JsonClassDiscriminator("backgroundType")
+public sealed class GroundType {
+    /**
+     * The color of the background.
+     */
+    public abstract var color: ColorWithAlpha
+
+    /**
+     * Represents a pure color background.
+     */
+    @SerialName("Color")
+    @Serializable
+    public data class Color(override var color: ColorWithAlpha = WHITE) : GroundType()
+
+    /**
+     * Represents a background with images.
+     *
+     * @property image The images to be used. When there's none, it clears the image background. When there are multiple, they will be played in a loop.
+     * @property color The color filter to be applied on images.
+     * @property fps The speed of the image loop in frames per second when there are multiple images.
+     * @property contentMode The content mode of the images.
+     * @property tilingConfig The tiling configuration of the images when [contentMode] is [ContentMode.TILED].
+     */
+    @SerialName("Image")
+    @Serializable(Image.Serializer::class)
+    @KeepGeneratedSerializer
+    public data class Image(
+        var image: List<String> = listOf(),
+        override var color: ColorWithAlpha = WHITE,
+        var fps: Double = 30.0,
+        var contentMode: ContentMode = ContentMode.SCALE_TO_FILL,
+        @Flatten
+        var tilingConfig: TilingConfig = TilingConfig()
+    ) : GroundType() {
+        public object Serializer : KSerializer<Image> by generatedSerializer().flatten()
+    }
+}
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
index 3508812..12bdf2e 100644
--- a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetBackgroundColorEvent.kt
@@ -4,71 +4,28 @@ package cn.rdlevel.rdkt.core.events
 
 
 import cn.rdlevel.rdkt.core.annotations.RDKTInternalAPI
-import cn.rdlevel.rdkt.core.data.*
-import cn.rdlevel.rdkt.core.data.action.ContentMode
+import cn.rdlevel.rdkt.core.data.ROOM1
+import cn.rdlevel.rdkt.core.data.RoomsOrTopLayer
+import cn.rdlevel.rdkt.core.data.action.GroundType
 import cn.rdlevel.rdkt.core.data.action.RescaleFilter
-import cn.rdlevel.rdkt.core.data.action.TilingConfig
+import cn.rdlevel.rdkt.core.data.roomsOf
 import cn.rdlevel.rdkt.core.serialization.Flatten
 import cn.rdlevel.rdkt.core.serialization.flatten
 import kotlinx.serialization.*
-import kotlinx.serialization.json.JsonClassDiscriminator
 
 /**
  * Sets the background of rooms.
  * @property type The type of the background.
  * @property filter How should the pixels' color of the background be when rescaled.
  */
-@ConsistentCopyVisibility
 @Serializable(SetBackgroundColorEvent.Serializer::class)
 @KeepGeneratedSerializer
 @SerialName("SetBackgroundColor")
-public data class SetBackgroundColorEvent private constructor(
+public data class SetBackgroundColorEvent(
     @Flatten
-    private var type: Type,
+    private var type: GroundType,
     var filter: RescaleFilter = RescaleFilter.NEAREST_NEIGHBOR,
     override val rooms: RoomsOrTopLayer = roomsOf(ROOM1),
 ) : ActionEvent(), RoomsOrTopLayerSpecificEvent {
-    /**
-     * Represents the type and the settings of the background.
-     */
-    @Serializable
-    @JsonClassDiscriminator("backgroundType")
-    public sealed class Type {
-        /**
-         * The color of the background.
-         */
-        public abstract var color: ColorWithAlpha
-
-        /**
-         * Represents a pure color background.
-         */
-        @SerialName("Color")
-        @Serializable
-        public data class Color(override var color: ColorWithAlpha = WHITE) : Type()
-
-        /**
-         * Represents a background with images.
-         *
-         * @property image The images to be used. When there's none, it clears the image background. When there are multiple, they will be played in a loop.
-         * @property color The color filter to be applied on images.
-         * @property fps The speed of the image loop in frames per second when there are multiple images.
-         * @property contentMode The content mode of the images.
-         * @property tilingConfig The tiling configuration of the images when [contentMode] is [ContentMode.TILED].
-         */
-        @SerialName("Image")
-        @Serializable(Image.Serializer::class)
-        @KeepGeneratedSerializer
-        public data class Image(
-            var image: List<String> = listOf(),
-            override var color: ColorWithAlpha = WHITE,
-            var fps: Double = 30.0,
-            var contentMode: ContentMode = ContentMode.SCALE_TO_FILL,
-            @Flatten
-            var tilingConfig: TilingConfig = TilingConfig()
-        ) : Type() {
-            public object Serializer : KSerializer<Image> by generatedSerializer().flatten()
-        }
-    }
-
     public object Serializer : KSerializer<SetBackgroundColorEvent> by generatedSerializer().flatten()
 }
\ No newline at end of file
diff --git a/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt
new file mode 100644
index 0000000..870fe25
--- /dev/null
+++ b/core/src/commonMain/kotlin/cn/rdlevel/rdkt/core/events/SetForegroundEvent.kt
@@ -0,0 +1,23 @@
+@file:OptIn(RDKTInternalAPI::class, ExperimentalSerializationApi::class)
+
+package cn.rdlevel.rdkt.core.events
+
+import cn.rdlevel.rdkt.core.annotations.RDKTInternalAPI
+import cn.rdlevel.rdkt.core.data.ROOM1
+import cn.rdlevel.rdkt.core.data.RoomsOrTopLayer
+import cn.rdlevel.rdkt.core.data.action.GroundType
+import cn.rdlevel.rdkt.core.data.roomsOf
+import cn.rdlevel.rdkt.core.serialization.Flatten
+import cn.rdlevel.rdkt.core.serialization.flatten
+import kotlinx.serialization.*
+
+@Serializable(SetForegroundEvent.Serializer::class)
+@KeepGeneratedSerializer
+@SerialName("SetForeground")
+public data class SetForegroundEvent(
+    @Flatten
+    private var type: GroundType.Image,
+    override val rooms: RoomsOrTopLayer = roomsOf(ROOM1),
+) : ActionEvent(), RoomsOrTopLayerSpecificEvent {
+    public object Serializer : KSerializer<SetForegroundEvent> by generatedSerializer().flatten()
+}