Track hovered sprite. End drag may transfer blocks from one sprite to another.

src/engine/adapter.js

@@ -152,7 +152,7 @@ const domToBlocks = function (blocksDOM) {
 /**
  * Adapter between block creation events and block representation which can be
  * used by the Scratch runtime.
- * @param {object} e `Blockly.events.create`
+ * @param {object} e `Blockly.events.create` or `Blockly.events.endDrag`
  * @return {Array.<object>} List of blocks from this CREATE event.
  */
 const adapter = function (e) {

src/virtual-machine.js

@@ -10,6 +10,7 @@ const sb3 = require('./serialization/sb3');
 const StringUtil = require('./util/string-util');
 const formatMessage = require('format-message');
 const Variable = require('./engine/variable');
+const adapter = require('./engine/adapter');
 
 const {loadCostume} = require('./import/load-costume.js');
 const {loadSound} = require('./import/load-sound.js');
@@ -40,6 +41,11 @@ class VirtualMachine extends EventEmitter {
          */
         this.editingTarget = null;
 
+        /**
+         * ID of sprite that mouse is hovered over in sprite selector, if any
+         */
+        this._hoveredSpriteId = null;
+
         /**
          * The currently dragging target, for redirecting IO data.
          * @type {Target}
@@ -553,6 +559,16 @@ class VirtualMachine extends EventEmitter {
         });
     }
 
+    /**
+     * Sets the hovered sprite
+     * @param {string} targetId ID of a target whose sprite to duplicate.
+     * @returns {Promise} Promise that resolves when duplicated target has
+     *     been added to the runtime.
+     */
+    setHoveredSprite (targetId) {
+        this._hoveredSpriteId = targetId;
+    }
+
     /**
      * Set the audio engine for the VM/runtime
      * @param {!AudioEngine} audioEngine The audio engine to attach
@@ -596,6 +612,26 @@ class VirtualMachine extends EventEmitter {
     blockListener (e) {
         if (this.editingTarget) {
             this.editingTarget.blocks.blocklyListen(e, this.runtime);
+
+            // Validate event
+            if (typeof e !== 'object') return;
+            if (typeof e.blockId !== 'string' && typeof e.varId !== 'string') {
+                return;
+            }
+
+            // Drag blocks onto another sprite
+            if (e.type === 'endDrag' &&
+                    e.isOutside &&
+                    this._hoveredSpriteId &&
+                    this._hoveredSpriteId !== this.editingTarget.id) {
+                const dragTarget = this.runtime.getTargetById(this._hoveredSpriteId);
+                if (dragTarget) {
+                    const newBlocks = adapter(e);
+                    for (let i = 0; i < newBlocks.length; i++) {
+                        dragTarget.blocks.createBlock(newBlocks[i]);
+                    }
+                }
+            }
         }
     }