polished comments for Kathy

svn: r2764

collects/htdch/draw/Canvas.java

@@ -14,9 +14,6 @@ public class Canvas {
   protected native boolean stop();
     // I need to figure out how to accomplish these two things, especially stop,
     // directly at the Scheme level w/o going thru the Java layer.
-    // BUG: this is actually a bug in ProfessorJ. Making these protected should 
-    // work just fine. Indeed, leaving off the access control qualifier should 
-    // work, too. (That's package protected.) 
      
   public native boolean show();
   public native boolean close();

collects/htdch/draw/support.scm

@@ -98,7 +98,16 @@
   
       (define (stop-native this accs gets privates)
 	(wrap-start-check ([hash-table-get privates '%end-of-time])))
-  
+
+      ;; (copy) restores the viewport and the pixmap so that
+      ;; (end-draw-sequence) can copy the pixmap into the viewport.
+      ;; It also clears the pixmap from anything that was on there.
+      ;; design rationale: the closure is created during the initializtion
+      ;; of the world (big-bang) and thus encapsulates access to the actual
+      ;; values of pixmap and viewport. big-bang exists once and for
+      ;; all and thus can't encapsulate the values.
+      ;; Alternative: expose these values as a "token", which big-bang must
+      ;; install. I couldn't figure out how to do this at the time. 
       (define (copy-native this accs gets privates)
 	(wrap-start-check ([hash-table-get privates 'copy])))
   
@@ -181,7 +190,7 @@
         void-or-true)
       
       (define (endOfTime-native this accs gets privates)
-        (define theCanvas ((hash-table-get accs 'theCanvas) this))
+        (define theCanvas ((hash-table-get accs 'theCanvas) this))	
         (send theCanvas stop)
         #t)
       

collects/htdp/big-draw.ss

@@ -226,6 +226,7 @@
                 #t)))
       (hash-table-put! h '%stop %stop)
       ;; --- 
+      ;; see ../htdch/draw/support.scm (copy) for explanation and design rationale
       (hash-table-put! h 'copy (lambda () (set! @vp vp*) (set! @pm pm*) [(clear-viewport pm*)]))
       ;; ---
       ;; --- the following can't happend during a draw sequence ---