recycle cached Canvasses in table views

HISTORY.md

@@ -3,6 +3,7 @@
 ## in development:
 * **New Features:**
 * **Notable Changes:**
+    * optimized loading projects
 * **Notable Fixes:**
 * **Translation Updates:**
 
@@ -15,6 +16,7 @@
 * widgets: recycle cached Canvasses
 * byob: recycle cached Canvasses
 * symbols: recycle cached Canvasses
+* symbols: recycle cached Canvasses
 
 ## 5.4.0:
 * **New Features:**

snap.html

@@ -13,7 +13,7 @@
         <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>
         <script type="text/javascript" src="src/byob.js?version=2020-01-03"></script>
-        <script type="text/javascript" src="src/tables.js?version=2019-06-27"></script>
+        <script type="text/javascript" src="src/tables.js?version=2020-01-03"></script>
         <script type="text/javascript" src="src/symbols.js?version=2020-01-03"></script>
         <script type="text/javascript" src="src/sketch.js?version=2019-10-09"></script>
         <script type="text/javascript" src="src/video.js?version=2019-06-27"></script>

src/tables.js

@@ -7,7 +7,7 @@
     written by Jens Mönig
     jens@moenig.org
 
-    Copyright (C) 2016 by Jens Mönig
+    Copyright (C) 2020 by Jens Mönig
 
     This file is part of Snap!.
 
@@ -64,13 +64,13 @@
 
 // Global settings /////////////////////////////////////////////////////
 
-/*global modules, Point, newCanvas, Morph, fontHeight, SliderMorph, List,
-MorphicPreferences, FrameMorph, HandleMorph, DialogBoxMorph, isString,
-SpriteMorph, Context, Costume, ArgMorph, BlockEditorMorph, SymbolMorph,
+/*global modules, Point, newCanvas, Morph, fontHeight, SliderMorph, isString,
+MorphicPreferences, FrameMorph, HandleMorph, DialogBoxMorph, StringMorph,
+SpriteMorph, Context, Costume, ArgMorph, BlockEditorMorph, SymbolMorph, List,
 SyntaxElementMorph, MenuMorph, SpriteBubbleMorph, SpeechBubbleMorph, Sound,
 CellMorph, ListWatcherMorph, isNil, BoxMorph, Variable, isSnapObject*/
 
-modules.tables = '2019-June-04';
+modules.tables = '2020-January-03';
 
 var Table;
 var TableCellMorph;
@@ -312,7 +312,7 @@ TableCellMorph.prototype.getData = function () {
 };
 
 TableCellMorph.prototype.drawNew = function () {
-    this.image = newCanvas(this.extent());
+    this.image = newCanvas(this.extent(), false, this.image);
     this.drawData();
 };
 
@@ -634,7 +634,7 @@ TableMorph.prototype.updateScrollBars = function () {
 
 TableMorph.prototype.drawNew = function () {
     var context, w, i;
-    this.image = newCanvas(this.extent());
+    this.image = newCanvas(this.extent(), false, this.image);
     context = this.image.getContext('2d');
     context.fillStyle = 'rgb(220, 220, 220)';
     BoxMorph.prototype.outlinePath.call(
@@ -824,7 +824,7 @@ TableMorph.prototype.update = function () {
 // TableMorph layout helpers (all private):
 
 TableMorph.prototype.rowLabelsWidth = function () {
-    var ctx = newCanvas().getContext('2d');
+    var ctx = StringMorph.prototype.measureCtx;
     ctx.font = 'italic ' + SyntaxElementMorph.prototype.fontSize +
         'px Helvetica, Arial, sans-serif';
     return Math.max(