Add horizontal scrolling of parallax layers

korge-fleks/src/commonMain/kotlin/korlibs/korge/fleks/components/MotionComponent.kt

@@ -4,6 +4,11 @@ import com.github.quillraven.fleks.*
 import korlibs.korge.fleks.utils.*
 import kotlinx.serialization.*
 
+/**
+ * A component to define movement for an entity.
+ *
+ * @param velocityX pixel/second (?)
+ */
 @Serializable @SerialName("Motion")
 data class MotionComponent(
     var accelX: Float = 0f,

korge-fleks/src/commonMain/kotlin/korlibs/korge/fleks/entity/config/ParallaxEffectConfig.kt

@@ -27,7 +27,7 @@ data class ParallaxEffectConfig(
                 y = this@ParallaxEffectConfig.y
             )  // global position for the whole parallax background
             it += MotionComponent(
-                velocityX = -12f  // world units per second
+                velocityX = -12f  // world units (16 pixels) per second (??? TODO: this needs to be ckecked)
             )
             it += ParallaxComponent(
                 name = assetName

korge-fleks/src/commonMain/kotlin/korlibs/korge/fleks/familyHooks/CameraFamily.kt

@@ -0,0 +1,21 @@
+package korlibs.korge.fleks.familyHooks
+
+import com.github.quillraven.fleks.*
+import korlibs.korge.fleks.components.*
+import korlibs.korge.fleks.tags.*
+
+/**
+ * Not needed because view port size is coming from entity config.
+ * Kept here for reference.
+ */
+val mainCameraFamily = World.family { all(SizeComponent, SizeIntComponent, MainCameraTag) }
+
+val onMainCameraAdded: FamilyHook = { entity ->
+    // Set view port half which is the middle point of the view port
+    val viewPortSize = entity[SizeIntComponent]
+    val viewPortHalf = entity[SizeComponent]
+    viewPortHalf.width = viewPortSize.width * 0.5f
+    viewPortHalf.height = viewPortSize.height * 0.5f
+
+    println("Set view port half: $viewPortHalf")
+}

korge-fleks/src/commonMain/kotlin/korlibs/korge/fleks/systems/CameraSystem.kt

@@ -24,6 +24,14 @@ class CameraSystem : IteratingSystem(
         cameraPosition.x += xDiff * 0.05f
         cameraPosition.y += yDiff * 0.05f
 
+        val parallaxFamily = world.family { all(ParallaxComponent, MotionComponent) }
+        parallaxFamily.forEach { parallaxEntity ->
+            val motion = parallaxEntity[MotionComponent]
+
+            // TODO: Check how we can convert pixel in pixel/second
+            motion.velocityX = -(xDiff * 0.05f) * 3f  // world units per second (?)
+        }
+
 
     }
 }

korge-fleks/src/commonMain/kotlin/korlibs/korge/fleks/systems/PositionSystem.kt

@@ -19,9 +19,6 @@ class PositionSystem : IteratingSystem(
     },
     interval = EachFrame
 ) {
-    private var camera: Entity = Entity.NONE  // Needs to be set after the camera entity was created after configuring the fleks world
-    private val viewPortSize: SizeInt = inject("ViewPortSize")
-
     // Overall world moving (playfield)
     val deltaX: Float = -110.0f  // TODO this will come from tiledMap scrolling
     val deltaY: Float = 0.0f
@@ -44,8 +41,4 @@ class PositionSystem : IteratingSystem(
             positionComponent.y = motion.accelX * 0.5f * deltaTime * deltaTime + motion.velocityY * deltaTime + positionComponent.y
         }
     }
-
-    fun setCamera(cameraName: String) {
-        this.camera = EntityByName.getOrNull(cameraName) ?: throw Error("ERROR: Camera entity with name $cameraName does not exist and cannot be set in PositionSystem!")
-    }
 }

korge-fleks/src/commonMain/kotlin/korlibs/korge/fleks/tags/MainCameraTag.kt

@@ -0,0 +1,12 @@
+package korlibs.korge.fleks.tags
+
+import com.github.quillraven.fleks.*
+import kotlinx.serialization.*
+
+/**
+ * The [MainCameraTag] component is used to specify which camera entity is used for rendering the game world.
+ * Make sure to have only one camera entity in the game world with has [MainCameraTag] component attached. Otherwise,
+ * the first camera entity found by the family search will be used for rendering.
+ */
+@Serializable @SerialName("MainCamera")
+data object MainCameraTag : EntityTag()