From c4cad3c6e4d4e3fac0e68a7c49e5f820152794ed Mon Sep 17 00:00:00 2001
From: Rachel Fenichel <fenichel@google.com>
Date: Fri, 17 Jun 2016 14:26:04 -0700
Subject: [PATCH] Cache screen CTM for performance improvement.

---
 core/scrollbar.js     |  3 ++-
 core/utils.js         |  5 ++---
 core/workspace_svg.js | 33 ++++++++++++++++++++++++++++++---
 3 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/core/scrollbar.js b/core/scrollbar.js
index ee080b0bc..6381b928f 100644
--- a/core/scrollbar.js
+++ b/core/scrollbar.js
@@ -606,7 +606,8 @@ Blockly.Scrollbar.prototype.onMouseDownBar_ = function(e) {
     e.stopPropagation();
     return;
   }
-  var mouseXY = Blockly.mouseToSvg(e, this.workspace_.getParentSvg());
+  var mouseXY = Blockly.mouseToSvg(e, this.workspace_.getParentSvg(),
+      this.workspace_.getInverseScreenCTM());
   var mouseLocation = this.horizontal_ ? mouseXY.x : mouseXY.y;
 
   var handleXY = Blockly.getSvgXY_(this.svgHandle_, this.workspace_);
diff --git a/core/utils.js b/core/utils.js
index 9b9e04d60..19ccc4cc8 100644
--- a/core/utils.js
+++ b/core/utils.js
@@ -308,14 +308,13 @@ Blockly.isRightButton = function(e) {
  * The origin (0,0) is the top-left corner of the Blockly svg.
  * @param {!Event} e Mouse event.
  * @param {!Element} svg SVG element.
+ * @param {SVGMatrix} matrix Inverted screen CTM to use.
  * @return {!Object} Object with .x and .y properties.
  */
-Blockly.mouseToSvg = function(e, svg) {
+Blockly.mouseToSvg = function(e, svg, matrix) {
   var svgPoint = svg.createSVGPoint();
   svgPoint.x = e.clientX;
   svgPoint.y = e.clientY;
-  var matrix = svg.getScreenCTM();
-  matrix = matrix.inverse();
   return svgPoint.matrixTransform(matrix);
 };
 
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index de636a7a2..4816349d2 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -144,6 +144,28 @@ Blockly.WorkspaceSvg.prototype.scrollbar = null;
  */
 Blockly.WorkspaceSvg.prototype.lastSound_ = null;
 
+/**
+ * Inverted screen CTM, for use in mouseToSvg.
+ * @type {SVGMatrix}
+ * @private
+ */
+Blockly.WorkspaceSvg.prototype.inverseScreenCTM_ = null;
+
+/**
+ * Getter for the inverted screen CTM.
+ * @return {SVGMatrix} The matrix to use in mouseToSvg
+ */
+Blockly.WorkspaceSvg.prototype.getInverseScreenCTM = function() {
+  return this.inverseScreenCTM_;
+};
+
+/**
+ * Update the inverted screen CTM.
+ */
+Blockly.WorkspaceSvg.prototype.updateInverseScreenCTM = function() {
+  this.inverseScreenCTM_ = this.getParentSvg().getScreenCTM().inverse();
+};
+
 /**
  * Save resize handler data so we can delete it later in dispose.
  * @param {!Array.<!Array>} handler Data that can be passed to unbindEvent_.
@@ -330,6 +352,7 @@ Blockly.WorkspaceSvg.prototype.resizeContents = function() {
     // based on contents.
     this.scrollbar.resize();
   }
+  this.updateInverseScreenCTM();
 };
 
 /**
@@ -355,6 +378,7 @@ Blockly.WorkspaceSvg.prototype.resize = function() {
   if (this.scrollbar) {
     this.scrollbar.resize();
   }
+  this.updateInverseScreenCTM();
 };
 
 /**
@@ -661,7 +685,8 @@ Blockly.WorkspaceSvg.prototype.onMouseDown_ = function(e) {
  */
 Blockly.WorkspaceSvg.prototype.startDrag = function(e, xy) {
   // Record the starting offset between the bubble's location and the mouse.
-  var point = Blockly.mouseToSvg(e, this.getParentSvg());
+  var point = Blockly.mouseToSvg(e, this.getParentSvg(),
+      this.getInverseScreenCTM());
   // Fix scale of mouse event.
   point.x /= this.scale;
   point.y /= this.scale;
@@ -674,7 +699,8 @@ Blockly.WorkspaceSvg.prototype.startDrag = function(e, xy) {
  * @return {!goog.math.Coordinate} New location of object.
  */
 Blockly.WorkspaceSvg.prototype.moveDrag = function(e) {
-  var point = Blockly.mouseToSvg(e, this.getParentSvg());
+  var point = Blockly.mouseToSvg(e, this.getParentSvg(),
+      this.getInverseScreenCTM());
   // Fix scale of mouse event.
   point.x /= this.scale;
   point.y /= this.scale;
@@ -690,7 +716,8 @@ Blockly.WorkspaceSvg.prototype.onMouseWheel_ = function(e) {
   // TODO: Remove terminateDrag and compensate for coordinate skew during zoom.
   Blockly.terminateDrag_();
   var delta = e.deltaY > 0 ? -1 : 1;
-  var position = Blockly.mouseToSvg(e, this.getParentSvg());
+  var position = Blockly.mouseToSvg(e, this.getParentSvg(),
+      this.getInverseScreenCTM());
   this.zoom(position.x, position.y, delta);
   e.preventDefault();
 };