worked around an asynchronous rendering issue

HISTORY.md

@@ -72,6 +72,7 @@
 ### 2021-12-09
 * blocks, threads: never push untested last minute changes that might break everything
 * gui: select motion category when switching to a scene that doesn't have the current custom category
+* objects: worked around an asynchronous rendering issue
 
 ### 2021-12-08
 * blocks: refactored syntax trees

snap.html

@@ -18,7 +18,7 @@
         <script src="src/widgets.js?version=2021-17-09"></script>
         <script src="src/blocks.js?version=2021-12-09"></script>
         <script src="src/threads.js?version=2021-12-09"></script>
-        <script src="src/objects.js?version=2021-12-07"></script>
+        <script src="src/objects.js?version=2021-12-09"></script>
         <script src="src/scenes.js?version=2021-11-24"></script>
         <script src="src/gui.js?version=2021-12-09"></script>
         <script src="src/paint.js?version=2021-07-05"></script>

src/objects.js

@@ -87,7 +87,7 @@ BlockVisibilityDialogMorph*/
 
 /*jshint esversion: 6*/
 
-modules.objects = '2021-November-07';
+modules.objects = '2021-November-09';
 
 var SpriteMorph;
 var StageMorph;
@@ -8076,7 +8076,10 @@ StageMorph.prototype.render = function (ctx) {
     ctx.save();
     ctx.fillStyle = this.color.toString();
     ctx.fillRect(0, 0, this.width(), this.height());
-    if (this.costume) {
+    if (this.costume &&
+        this.costume.contents.width &&
+        this.costume.contents.height
+    ) {
         ctx.scale(this.scale, this.scale);
         ctx.drawImage(
             this.costume.contents,
@@ -8084,6 +8087,9 @@ StageMorph.prototype.render = function (ctx) {
             (this.height() / this.scale - this.costume.height()) / 2
         );
         this.cachedImage = this.applyGraphicsEffects(this.cachedImage);
+    } else { // deal with async asset creation
+        this.costume = null;
+        this.cachedImage = null;
     }
     ctx.restore();
     this.version = Date.now(); // for observer optimization