Use targetWasCreated event to clone pen state

Remove explicit cloning of `_customState` in favor of smarter,
state-specific cloning.

src/blocks/scratch3_pen.js

@@ -40,7 +40,10 @@ class Scratch3PenBlocks {
          */
         this._penSkinId = -1;
 
+        this._onTargetCreated = this._onTargetCreated.bind(this);
         this._onTargetMoved = this._onTargetMoved.bind(this);
+
+        runtime.on('targetWasCreated', this._onTargetCreated);
     }
 
     /**
@@ -129,6 +132,25 @@ class Scratch3PenBlocks {
         return penState;
     }
 
+    /**
+     * When a pen-using Target is cloned, clone the pen state.
+     * @param {Target} newTarget - the newly created target.
+     * @param {Target} [sourceTarget] - the target used as a source for the new clone, if any.
+     * @listens Runtime#event:targetWasCreated
+     * @private
+     */
+    _onTargetCreated (newTarget, sourceTarget) {
+        if (sourceTarget) {
+            const penState = sourceTarget.getCustomState(Scratch3PenBlocks.STATE_KEY);
+            if (penState) {
+                newTarget.setCustomState(Scratch3PenBlocks.STATE_KEY, Clone.simple(penState));
+                if (penState.penDown) {
+                    newTarget.addListener(RenderedTarget.EVENT_TARGET_MOVED, this._onTargetMoved);
+                }
+            }
+        }
+    }
+
     /**
      * Handle a target which has moved. This only fires when the pen is down.
      * @param {RenderedTarget} target - the target which has moved.

src/engine/runtime.js

@@ -968,6 +968,16 @@ class Runtime extends EventEmitter {
         return this._cloneCounter < Runtime.MAX_CLONES;
     }
 
+    /**
+     * Report that a new target has been created, possibly by cloning an existing target.
+     * @param {Target} newTarget - the newly created target.
+     * @param {Target} [sourceTarget] - the target used as a source for the new clone, if any.
+     * @fires Runtime#targetWasCreated
+     */
+    fireTargetWasCreated (newTarget, sourceTarget) {
+        this.emit('targetWasCreated', newTarget, sourceTarget);
+    }
+
     /**
      * Get a target representing the Scratch stage, if one exists.
      * @return {?Target} The target, if found.
@@ -1014,4 +1024,12 @@ class Runtime extends EventEmitter {
     }
 }
 
+/**
+ * Event fired after a new target has been created, possibly by cloning an existing target.
+ *
+ * @event Runtime#targetWasCreated
+ * @param {Target} newTarget - the newly created target.
+ * @param {Target} [sourceTarget] - the target used as a source for the new clone, if any.
+ */
+
 module.exports = Runtime;

src/sprites/rendered-target.js

@@ -732,7 +732,6 @@ class RenderedTarget extends Target {
         newClone.effects = JSON.parse(JSON.stringify(this.effects));
         newClone.variables = JSON.parse(JSON.stringify(this.variables));
         newClone.lists = JSON.parse(JSON.stringify(this.lists));
-        newClone._customState = JSON.parse(JSON.stringify(this._customState));
         newClone.initDrawable();
         newClone.updateAllDrawableProperties();
         // Place behind the current target.

src/sprites/sprite.js

@@ -55,6 +55,9 @@ class Sprite {
         this.clones.push(newClone);
         if (newClone.isOriginal) {
             newClone.initDrawable();
+            this.runtime.fireTargetWasCreated(newClone);
+        } else {
+            this.runtime.fireTargetWasCreated(newClone, this.clones[0]);
         }
         return newClone;
     }