added dimension getters for the stage

HISTORY.md

@@ -2,7 +2,7 @@
 
 ## in development:
 * **New Features:**
-    * added selectors for sprites' bounding box (left, right, top, bottom) to MY dropdown
+    * added selectors for sprites' and the stage's bounding box (left, right, top, bottom) to MY dropdown
 * **Notable Changes:**
     * running STOP ALL now also toggles (pauses and resumes) all generic WHEN hat blocks (just like pressing the stop button)
 * **Notable Fixes:**
@@ -10,6 +10,9 @@
     * assert that dimensions given for STRETCH are finite numbers (avoid crash)
 * **Translation Updates:**
 
+### 2019-10-18
+* objects, blocks, threads: added dimension getters for the stage
+
 ### 2019-10-17
 * objects, blocks, threads: added selectors for sprites' bounding box (left, right, top, bottom) to MY dropdown
 

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=2019-10-17"></script>
         <script type="text/javascript" src="src/threads.js?version=2019-10-17"></script>
-        <script type="text/javascript" src="src/objects.js?version=2019-10-17"></script>
+        <script type="text/javascript" src="src/objects.js?version=2019-10-18"></script>
         <script type="text/javascript" src="src/gui.js?version=2019-10-16"></script>
         <script type="text/javascript" src="src/paint.js?version=2019-06-27"></script>
         <script type="text/javascript" src="src/lists.js?version=2019-07-01"></script>

src/objects.js

@@ -84,7 +84,7 @@ BlockEditorMorph, BlockDialogMorph, PrototypeHatBlockMorph,  BooleanSlotMorph,
 localize, TableMorph, TableFrameMorph, normalizeCanvas, VectorPaintEditorMorph,
 HandleMorph, AlignmentMorph, Process, XML_Element, WorldMap*/
 
-modules.objects = '2019-October-17';
+modules.objects = '2019-October-18';
 
 var SpriteMorph;
 var StageMorph;
@@ -9034,6 +9034,32 @@ StageMorph.prototype.getLastAnswer
 StageMorph.prototype.reportThreadCount
     = SpriteMorph.prototype.reportThreadCount;
 
+// StageMorph dimension getters
+
+StageMorph.prototype.xCenter = function () {
+    return 0;
+};
+
+StageMorph.prototype.yCenter = function () {
+    return 0;
+};
+
+StageMorph.prototype.xLeft = function () {
+    return this.dimensions.x * -0.5;
+};
+
+StageMorph.prototype.xRight = function () {
+   return this.dimensions.x / 2;
+};
+
+StageMorph.prototype.yTop = function () {
+    return this.dimensions.y / 2;
+};
+
+StageMorph.prototype.yBottom = function () {
+   return this.dimensions.y * -0.5;
+};
+
 // StageMorph message broadcasting
 
 StageMorph.prototype.allMessageNames