From df7f534ad6ed287ecc8d13c4e159138b71ed1e88 Mon Sep 17 00:00:00 2001
From: Rachel Fenichel <fenichel@google.com>
Date: Thu, 17 May 2018 11:05:18 -0700
Subject: [PATCH] Performance improvements for workspace clear and load

---
 core/block_svg.js | 30 +++++++++++++++++++++---------
 core/workspace.js | 44 ++++++++++++++++++++++++++++----------------
 core/xml.js       | 15 +++++++++++++++
 3 files changed, 64 insertions(+), 25 deletions(-)

diff --git a/core/block_svg.js b/core/block_svg.js
index 313103794..a073aacf0 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -252,28 +252,40 @@ Blockly.BlockSvg.prototype.getIcons = function() {
  * @param {Blockly.BlockSvg} newParent New parent block.
  */
 Blockly.BlockSvg.prototype.setParent = function(newParent) {
-  if (newParent == this.parentBlock_) {
+  var oldParent = this.parentBlock_;
+  if (newParent == oldParent) {
     return;
   }
-  var svgRoot = this.getSvgRoot();
-  if (this.parentBlock_ && svgRoot) {
-    // Move this block up the DOM.  Keep track of x/y translations.
-    var xy = this.getRelativeToSurfaceXY();
-    this.workspace.getCanvas().appendChild(svgRoot);
-    svgRoot.setAttribute('transform', 'translate(' + xy.x + ',' + xy.y + ')');
-  }
 
   Blockly.Field.startCache();
   Blockly.BlockSvg.superClass_.setParent.call(this, newParent);
   Blockly.Field.stopCache();
 
+  var svgRoot = this.getSvgRoot();
+
+  // Bail early if workspace is clearing, or we aren't rendered.
+  // We won't need to reattach ourselves anywhere.
+  if (this.workspace.isClearing || !svgRoot) {
+    return;
+  }
+
+  var oldXY = this.getRelativeToSurfaceXY();
   if (newParent) {
-    var oldXY = this.getRelativeToSurfaceXY();
     newParent.getSvgRoot().appendChild(svgRoot);
     var newXY = this.getRelativeToSurfaceXY();
     // Move the connections to match the child's new position.
     this.moveConnections_(newXY.x - oldXY.x, newXY.y - oldXY.y);
   }
+  // If we are losing a parent, we want to move our DOM element to the
+  // root of the workspace.
+  else if (oldParent) {
+    // Avoid moving a block up the DOM if it's currently selected/dragging,
+    // so as to avoid taking things off the drag surface.
+    if (Blockly.selected != this) {
+      this.workspace.getCanvas().appendChild(svgRoot);
+      this.translate(oldXY.x, oldXY.y);
+    }
+  }
 };
 
 /**
diff --git a/core/workspace.js b/core/workspace.js
index 13815f7d2..2bb088c52 100644
--- a/core/workspace.js
+++ b/core/workspace.js
@@ -115,6 +115,13 @@ Blockly.Workspace = function(opt_options) {
  */
 Blockly.Workspace.prototype.rendered = false;
 
+/**
+ * Returns `true` if the workspace is currently in the process of a bulk clear.
+ * @type {boolean}
+ * @package
+ */
+Blockly.Workspace.prototype.isClearing = false;
+
 /**
  * Maximum number of undo events in stack. `0` turns off undo, `Infinity` sets it to unlimited.
  * @type {number}
@@ -264,22 +271,27 @@ Blockly.Workspace.prototype.getAllBlocks = function(ordered) {
  * Dispose of all blocks and comments in workspace.
  */
 Blockly.Workspace.prototype.clear = function() {
-  var existingGroup = Blockly.Events.getGroup();
-  if (!existingGroup) {
-    Blockly.Events.setGroup(true);
-  }
-  while (this.topBlocks_.length) {
-    this.topBlocks_[0].dispose();
-  }
-  while (this.topComments_.length) {
-    this.topComments_[this.topComments_.length - 1].dispose();
-  }
-  if (!existingGroup) {
-    Blockly.Events.setGroup(false);
-  }
-  this.variableMap_.clear();
-  if (this.potentialVariableMap_) {
-    this.potentialVariableMap_.clear();
+  this.isClearing = true;
+  try {
+    var existingGroup = Blockly.Events.getGroup();
+    if (!existingGroup) {
+      Blockly.Events.setGroup(true);
+    }
+    while (this.topBlocks_.length) {
+      this.topBlocks_[0].dispose();
+    }
+    while (this.topComments_.length) {
+      this.topComments_[this.topComments_.length - 1].dispose();
+    }
+    if (!existingGroup) {
+      Blockly.Events.setGroup(false);
+    }
+    this.variableMap_.clear();
+    if (this.potentialVariableMap_) {
+      this.potentialVariableMap_.clear();
+    }
+  } finally {
+    this.isClearing = false;
   }
 };
 
diff --git a/core/xml.js b/core/xml.js
index 15199c1ac..744274629 100644
--- a/core/xml.js
+++ b/core/xml.js
@@ -364,6 +364,21 @@ Blockly.Xml.textToDom = function(text) {
   return dom.firstChild;
 };
 
+/**
+ * Clear the given workspace then decode an XML DOM and
+ * create blocks on the workspace.
+ * @param {!Element} xml XML DOM.
+ * @param {!Blockly.Workspace} workspace The workspace.
+ * @return {Array.<string>} An array containing new block ids.
+ */
+Blockly.Xml.clearWorkspaceAndLoadFromXml = function(xml, workspace) {
+  workspace.setResizesEnabled(false);
+  workspace.clear();
+  var blockIds = Blockly.Xml.domToWorkspace(xml, workspace);
+  workspace.setResizesEnabled(true);
+  return blockIds;
+};
+
 /**
  * Decode an XML DOM and create blocks on the workspace.
  * @param {!Element} xml XML DOM.