new example, bug fixes

  * add `VBox` and `HBox` to layout data blocks without the need to play
-   with Heaps (fix `examples/qs-main.py` accordingly)
+   with Heaps (fix examples accordingly)

@@ -87,16 +87,19 @@ class CAniTikZ (CAni) :
                              % (key, self.__class__.__name__))
     def ptr (self) :
         return Pointer(self)
-    def tex (self, **tikz) :
+    def tex (self, head=None, tail=None, **tikz) :
         opt = TikZ(tikz)
         return cleandoc(r"""\begin{{tikzpicture}}[{opt.tikzpicture}]
-          {code}
+          {head}{code}{tail}
         \end{{tikzpicture}}
-        """).format(opt=opt, code="\n  ".join(self.tikz(**tikz).splitlines()))
+        """).format(opt=opt,
+                    head=(head + "\n") if head else "",
+                    tail=("\n" + tail) if tail else "",
+                    code="\n  ".join(self.tikz(**tikz).splitlines()))
 
 class Pointer (CAniTikZ) :
     def __init__ (self, data) :
-        self._d = data
+        self.__dict__.update(_d=data, nodeid=None)
     def val (self) :
         return self._d
     def __tikz__ (self, src, opt) :
@@ -109,6 +112,10 @@ class Pointer (CAniTikZ) :
         return self._d[key]
     def __setitem__ (self, key, val) :
         self._d[key] = val
+    def __getattr__ (self, key) :
+        return getattr(self._d, key)
+    def __setattr__ (self, key, val) :
+        setattr(self._d, key, val)
 
 class Value (CAniTikZ) :
     def __init__ (self, init=None, **tikz) :

-all: heap.pdf qs-partition.pdf qs-main.pdf
+all: heap.pdf qs-partition.pdf qs-main.pdf stack-push.pdf
+gif: qs-partition.gif qs-main.gif stack-push.gif
+mp4: qs-partition.mp4 qs-main.mp4 stack-push.mp4
 
 %.pdf: %.py tpl.tex
 	ln -sf ../codanim .
@@ -8,5 +10,22 @@ all: heap.pdf qs-partition.pdf qs-main.pdf
 	pdflatex tpl
 	cp tpl.pdf $@
 
+%.gif: %.pdf
+	rm -rf _gif
+	mkdir _gif
+	gs -dSAFER -DBATCH -dNOPAUSE -sDEVICE=png16m -r400 -sOutputFile=_gif/%03d.png $<
+	mogrify -resize 800x600 -format gif _gif/*.png
+	gifsicle -k64 -d80 -l0 _gif/*.gif -O2 -o $@
+	rm -rf _gif
+
+%.mp4: %.pdf
+	rm -rf _mp4
+	mkdir _mp4
+	gs -dSAFER -DBATCH -dNOPAUSE -sDEVICE=png16m -r400 -sOutputFile=_mp4/%03d.png $<
+	ffmpeg -r 1 -s 1024x768 -i _mp4/%03d.png -vcodec libx264 -crf 25 -pix_fmt yuv420p $@
+	rm -rf _mp4
+
 clean:
 	rm -f out.* $$(grep '^*' ../.gitignore)
+	rm -rf _gif
+	rm -rf _mp4

+from codanim.data import Heap, Struct, Value
+from codanim.flow import FUNC, BLOCK, ENV, WS, DECL, EXPR, STMT
+
+heap = Heap()
+
+stack = heap.new(Struct({"val": Value(1), "next": None}))
+stack = heap.new(Struct({"val": Value(2), "next": stack}))
+s = Value(stack, nodeid="s")
+t = Value(None, nodeid="t", value={"xshift": "-25mm"})
+
+v = Heap(heap={"grow": "above",
+               "separation": "0pt"})
+h = Heap(heap={"grow": "right"},
+         )
+h.new(t)
+h.new(s)
+v.new(heap)
+v.new(h)
+
+push = FUNC(BLOCK(ENV("s", s),
+                  ENV("u", Value(3)),
+                  ENV("top", t),
+                  ENV("new", heap.new),
+                  ENV("Struct", Struct),
+                  ENV("Value", Value),
+                  WS("\n  "),
+                  DECL("top", EXPR("new(Struct({'val': None, 'next': None}))",
+                                   src="malloc(sizeof(StackCell))"),
+                       src="Stack {name} = {init};"),
+                  WS("\n  "),
+                  STMT("top.val = u", src="top->val = u;"),
+                  WS("\n  "),
+                  STMT("top.next = s", src="top->next = *s;"),
+                  WS("\n  "),
+                  STMT("s = top", src="*s = top;"),
+                  WS("\n")),
+            src="void stackPush (Stack* s, uint u) {{{body}}}\n")
+
+# run code and save its animation
+push.IP += 1
+push()
+with open("out.code", "w") as out :
+    out.write(push.tex())
+
+# save data and animation
+with open("out.tikz", "w") as out :
+    out.write(v.tex(tail=r"""
+    \node[above] at (s.north) {\texttt{s}};
+    \node[above] at (t.north) {\texttt{top}};
+    """))