Disable resizing the workspace during clearing and loading from xml, as an optimization

core/block_svg.js

@@ -264,7 +264,8 @@ Blockly.BlockSvg.terminateDrag = function() {
       delete selected.draggedBubbles_;
       selected.setDragging_(false);
       selected.render();
-      // Ensure that any stap and bump are part of this move's event group.
+      selected.workspace.setResizesEnabled(true);
+      // Ensure that any snap and bump are part of this move's event group.
       var group = Blockly.Events.getGroup();
       setTimeout(function() {
         Blockly.Events.setGroup(group);
@@ -276,8 +277,6 @@ Blockly.BlockSvg.terminateDrag = function() {
         selected.bumpNeighbours_();
         Blockly.Events.setGroup(false);
       }, Blockly.BUMP_DELAY);
-      // Fire an event to allow scrollbars to resize.
-      selected.workspace.resizeContents();
     }
   }
   Blockly.dragMode_ = Blockly.DRAG_NONE;
@@ -870,6 +869,7 @@ Blockly.BlockSvg.prototype.onMouseMove_ = function(e) {
       // Switch to unrestricted dragging.
       Blockly.dragMode_ = Blockly.DRAG_FREE;
       Blockly.longStop_();
+      this.workspace.setResizesEnabled(false);
       if (this.parentBlock_) {
         // Push this block to the very top of the stack.
         this.unplug();

core/flyout.js

@@ -1109,6 +1109,8 @@ Blockly.Flyout.prototype.createBlockFunc_ = function(originBlock) {
     block.onMouseDown_(e);
     Blockly.dragMode_ = Blockly.DRAG_FREE;
     block.setDragging_(true);
+    // Disable workspace resizing.  Reenable at the end of the drag.
+    flyout.targetWorkspace_.setResizesEnabled(false);
   };
 };
 

core/workspace_svg.js

@@ -103,6 +103,14 @@ Blockly.WorkspaceSvg.prototype.isMutator = false;
  */
 Blockly.WorkspaceSvg.prototype.dragMode_ = Blockly.DRAG_NONE;
 
+/**
+ * Whether this workspace has resizes enabled.
+ * Disable during batch operations for a performance improvement.
+ * @type {boolean}
+ * @private
+ */
+Blockly.WorkspaceSvg.prototype.resizesEnabled_ = true;
+
 /**
  * Current horizontal scrolling offset.
  * @type {number}
@@ -260,7 +268,7 @@ Blockly.WorkspaceSvg.prototype.createDom = function(opt_backgroundClass) {
   // Determine if there needs to be a category tree, or a simple list of
   // blocks.  This cannot be changed later, since the UI is very different.
   if (this.options.hasCategories) {
-    /** 
+    /**
      * @type {Blockly.Toolbox}
      * @private
      */
@@ -389,12 +397,15 @@ Blockly.WorkspaceSvg.prototype.updateScreenCalculations_ = function() {
 };
 
 /**
- * Resize the parts of the workspace that change when the workspace
+ * If enabled, resize the parts of the workspace that change when the workspace
  * contents (e.g. block positions) change.  This will also scroll the
  * workspace contents if needed.
  * @package
  */
 Blockly.WorkspaceSvg.prototype.resizeContents = function() {
+  if (!this.resizesEnabled_) {
+    return;
+  }
   if (this.scrollbar) {
     // TODO(picklesrus): Once rachel-fenichel's scrollbar refactoring
     // is complete, call the method that only resizes scrollbar
@@ -1423,6 +1434,32 @@ Blockly.WorkspaceSvg.setTopLevelWorkspaceMetrics_ = function(xyRatio) {
     }
   }
 };
+
+/**
+ * Update whether this workspace has resizes enabled.
+ * If enabled, workspace will resize when appropriate.
+ * If disabled, workspace will not resize until re-enabled.
+ * Use to avoid resizing during a batch operation, for performance.
+ * @param {boolean} enabled Whether resizes should be enabled.
+ */
+Blockly.WorkspaceSvg.prototype.setResizesEnabled = function(enabled) {
+  var reenabled = (!this.resizesEnabled_ && enabled);
+  this.resizesEnabled_ = enabled;
+  if (reenabled) {
+    // Newly enabled.  Trigger a resize.
+    this.resizeContents();
+  }
+};
+
+/**
+ * Dispose of all blocks in workspace, with an optimization to prevent resizes.
+ */
+Blockly.WorkspaceSvg.prototype.clear = function() {
+  this.setResizesEnabled(false);
+  Blockly.WorkspaceSvg.superClass_.clear.call(this);
+  this.setResizesEnabled(true);
+};
+
 // Export symbols that would otherwise be renamed by Closure compiler.
 Blockly.WorkspaceSvg.prototype['setVisible'] =
     Blockly.WorkspaceSvg.prototype.setVisible;

core/xml.js

@@ -296,6 +296,11 @@ Blockly.Xml.domToWorkspace = function(xml, workspace) {
   if (!existingGroup) {
     Blockly.Events.setGroup(true);
   }
+
+  // Disable workspace resizes as an optimization.
+  if (workspace.setResizesEnabled) {
+    workspace.setResizesEnabled(false);
+  }
   for (var i = 0; i < childCount; i++) {
     var xmlChild = xml.childNodes[i];
     var name = xmlChild.nodeName.toLowerCase();
@@ -320,6 +325,10 @@ Blockly.Xml.domToWorkspace = function(xml, workspace) {
   Blockly.Field.stopCache();
 
   workspace.updateVariableList(false);
+  // Re-enable workspace resizing.
+  if (workspace.setResizesEnabled) {
+    workspace.setResizesEnabled(true);
+  }
 };
 
 /**