UINSMenu is made to show how to code 'UI dragging'

src/net/torvald/terrarum/ui/UICanvas.kt

@@ -3,6 +3,7 @@ package net.torvald.terrarum.ui
 import com.badlogic.gdx.Gdx
 import com.badlogic.gdx.graphics.Camera
 import com.badlogic.gdx.graphics.g2d.SpriteBatch
+import net.torvald.terrarum.AppLoader
 import net.torvald.terrarum.Terrarum
 import net.torvald.terrarum.Second
 import net.torvald.terrarum.roundInt
@@ -80,7 +81,12 @@ abstract class UICanvas(
 
     /** Override this for the actual update. Note that you must update uiItems by yourself. */
     abstract fun updateUI(delta: Float)
-    /** Override this for the actual render. Note that you must render uiItems by yourself. */
+    /**
+     * Override this for the actual render. Note that you must render uiItems by yourself.
+     *
+     * Under normal circumstances, draws are automatically translated as per the handler's X/Y position.
+     * This means, don't write like: ```draw(posX + 4, posY + 32)```, do instead: ```draw(4, 32)``` unless you have a good reason to do so.
+     */
     abstract fun renderUI(batch: SpriteBatch, camera: Camera)
 
     /**
@@ -109,6 +115,8 @@ abstract class UICanvas(
         uiItems.add(uiItem)
     }
 
+    fun mouseInScreen(x: Int, y: Int) = x in 0 until AppLoader.appConfig.width && y in 0 until AppLoader.appConfig.height
+
     open fun mouseMoved(screenX: Int, screenY: Int): Boolean {
         if (this.isVisible) {
             uiItems.forEach { it.mouseMoved(screenX, screenY) }
@@ -117,6 +125,10 @@ abstract class UICanvas(
         }
         else return false
     }
+
+    /**
+     * When implementing this, make sure to use ```mouseInScreen()``` function!
+     */
     open fun touchDragged(screenX: Int, screenY: Int, pointer: Int): Boolean {
         if (this.isVisible) {
             uiItems.forEach { it.touchDragged(screenX, screenY, pointer) }
@@ -126,7 +138,7 @@ abstract class UICanvas(
         else return false
     }
     open fun touchDown(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {
-        if (this.isVisible) {
+        if (this.isVisible && mouseInScreen(screenX, screenY)) {
             uiItems.forEach { it.touchDown(screenX, screenY, pointer, button) }
             handler.subUIs.forEach { it.touchDown(screenX, screenY, pointer, button) }
             return true

src/net/torvald/terrarum/ui/UIItem.kt

@@ -107,6 +107,10 @@ abstract class UIItem(var parentUI: UICanvas) { // do not replace parentUI to UI
             }
         }
     }
+
+    /**
+     * In this time, you do write like: ```draw(posX + 4, posY + 32)```, unlike UICanvas, because posX/posY comes from the parent UI.
+     */
     open fun render(batch: SpriteBatch, camera: Camera) {
         if (parentUI.isVisible) {
             mouseOverCall?.render(batch, camera)

src/net/torvald/terrarum/ui/UINSMenu.kt

@@ -17,8 +17,9 @@ class UINSMenu(
 
         val titleBackCol: Color = Color(0f,0f,0f,.77f),
         val titleTextCol: Color = Color.WHITE,
-        val titleBlendMode: String = BlendMode.NORMAL
+        val titleBlendMode: String = BlendMode.NORMAL,
 
+        val allowDrag: Boolean = true
 ) : UICanvas() {
 
     override var openCloseTime: Second = 0f
@@ -59,11 +60,11 @@ class UINSMenu(
         // draw title bar
         batch.color = titleBackCol
         BlendMode.resolve(titleBlendMode, batch)
-        batch.fillRect(posX.toFloat(), posY.toFloat(), width.toFloat(), LINE_HEIGHT.toFloat())
+        batch.fillRect(0f, 0f, width.toFloat(), LINE_HEIGHT.toFloat())
 
         batch.color = titleTextCol
         blendNormal(batch)
-        Terrarum.fontGame.draw(batch, title, posX + TEXT_OFFSETX, posY + TEXT_OFFSETY)
+        Terrarum.fontGame.draw(batch, title, TEXT_OFFSETX, TEXT_OFFSETY)
 
         // draw the list
         batch.color = Color.WHITE
@@ -74,6 +75,9 @@ class UINSMenu(
         theRealList.dispose()
     }
 
+    fun mouseOnTitleBar() =
+            relativeMouseX in 0 until width && relativeMouseY in 0 until LINE_HEIGHT
+
     override fun doOpening(delta: Float) {
     }
 
@@ -90,12 +94,34 @@ class UINSMenu(
         return super.mouseMoved(screenX, screenY)
     }
 
+    private var dragOriginX = 0 // relative mousepos
+    private var dragOriginY = 0 // relative mousepos
+    private var dragForReal = false
+
     override fun touchDragged(screenX: Int, screenY: Int, pointer: Int): Boolean {
-        return super.touchDragged(screenX, screenY, pointer)
+        if (!allowDrag) return false
+
+        if (mouseInScreen(screenX, screenY)) {
+            if (dragForReal) {
+                handler.setPosition(screenX - dragOriginX, screenY - dragOriginY)
+                println("drag $screenX, $screenY")
+            }
+        }
+
+        return true
     }
 
     override fun touchDown(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {
-        return super.touchDown(screenX, screenY, pointer, button)
+        if (mouseOnTitleBar()) {
+            dragOriginX = relativeMouseX
+            dragOriginY = relativeMouseY
+            dragForReal = true
+        }
+        else {
+            dragForReal = false
+        }
+
+        return true
     }
 
     override fun touchUp(screenX: Int, screenY: Int, pointer: Int, button: Int): Boolean {