recycle cached Canvasses in watchers

HISTORY.md

@@ -8,8 +8,9 @@
 
 ### 2020-01-03
 * new dev version
-* Morphic: recycle cached Canvasses
+* morphic: recycle cached Canvasses
 * gui: recycle cached Canvasses
+* objects: recycle cached Canvasses
 
 ## 5.4.0:
 * **New Features:**

snap.html

@@ -8,7 +8,7 @@
         <script type="text/javascript" src="src/widgets.js?version=2019-10-16"></script>
         <script type="text/javascript" src="src/blocks.js?version=2019-12-13"></script>
         <script type="text/javascript" src="src/threads.js?version=2019-12-19"></script>
-        <script type="text/javascript" src="src/objects.js?version=2019-12-19"></script>
+        <script type="text/javascript" src="src/objects.js?version=2020-01-03"></script>
         <script type="text/javascript" src="src/gui.js?version=2020-01-03"></script>
         <script type="text/javascript" src="src/paint.js?version=2019-06-27"></script>
         <script type="text/javascript" src="src/lists.js?version=2019-12-08"></script>

src/objects.js

@@ -9,7 +9,7 @@
     written by Jens Mönig
     jens@moenig.org
 
-    Copyright (C) 2019 by Jens Mönig
+    Copyright (C) 2020 by Jens Mönig
 
     This file is part of Snap!.
 
@@ -84,7 +84,7 @@ BlockEditorMorph, BlockDialogMorph, PrototypeHatBlockMorph,  BooleanSlotMorph,
 localize, TableMorph, TableFrameMorph, normalizeCanvas, VectorPaintEditorMorph,
 HandleMorph, AlignmentMorph, Process, XML_Element, WorldMap, copyCanvas*/
 
-modules.objects = '2019-December-19';
+modules.objects = '2020-January-03';
 
 var SpriteMorph;
 var StageMorph;
@@ -10968,7 +10968,7 @@ CellMorph.prototype.drawNew = function (toggle, type) {
     ));
 
     // draw my outline
-    this.image = newCanvas(this.extent());
+    this.image = newCanvas(this.extent(), false, this.image);
     context = this.image.getContext('2d');
     if ((this.edge === 0) && (this.border === 0)) {
         BoxMorph.uber.drawNew.call(this);
@@ -11057,7 +11057,7 @@ CellMorph.prototype.layoutChanged = function () {
 
 
     // draw my outline
-    this.image = newCanvas(this.extent());
+    this.image = newCanvas(this.extent(), false, this.image);
     context = this.image.getContext('2d');
     if ((this.edge === 0) && (this.border === 0)) {
         BoxMorph.uber.drawNew.call(this);
@@ -11830,7 +11830,7 @@ WatcherMorph.prototype.userSetSliderMax = function () {
 WatcherMorph.prototype.drawNew = function () {
     var context,
         gradient;
-    this.image = newCanvas(this.extent());
+    this.image = newCanvas(this.extent(), false, this.image);
     context = this.image.getContext('2d');
     if (MorphicPreferences.isFlat || (this.edge === 0 && this.border === 0)) {
         BoxMorph.uber.drawNew.call(this);