Add support for 'streaming mode' which draws animated graphs from stdin

tests/streaming.sh

@@ -0,0 +1,57 @@
+while true; do
+
+    cat <<EOF
+digraph {
+  A -> B;
+}
+
+EOF
+    printf '\0'
+    sleep 1
+
+    cat <<EOF
+digraph {
+  A -> B;
+  B -> C;
+}
+
+EOF
+    printf '\0'
+    sleep 1
+
+    cat <<EOF
+digraph {
+  A -> B;
+  B -> C;
+  B -> D;
+}
+
+EOF
+    printf '\0'
+    sleep 1
+
+    cat <<EOF
+digraph {
+  A -> B;
+  B -> C;
+  B -> D;
+  C -> E;
+}
+
+EOF
+    printf '\0'
+    sleep 1
+
+    cat <<EOF
+digraph {
+  A -> B;
+  B -> C;
+  B -> D;
+  C -> E;
+  D -> E;
+}
+
+EOF
+    printf '\0'
+    sleep 1
+done

xdot/__main__.py

@@ -18,6 +18,7 @@
 
 import argparse
 import sys
+from threading import Thread
 
 from .ui.window import DotWindow, Gtk
 
@@ -61,6 +62,10 @@ def main():
         '--hide-toolbar',
         action='store_true', dest='hide_toolbar',
         help='Hides the toolbar on start.')
+    parser.add_argument(
+        '--streaming-mode',
+        action='store_true', dest='streaming_mode',
+        help='Updates canvas when a new graph is read from stdin')
 
     options = parser.parse_args()
     inputfile = options.inputfile
@@ -89,7 +94,32 @@ def main():
         import signal
         signal.signal(signal.SIGINT, signal.SIG_DFL)
 
+    def read():
+        istream = sys.stdin.detach()
+        buf = bytearray()
+        first = True
+        # if there's a more efficient way to do this than to scan
+        # stdin character by character, I'm all for it. This just gets
+        # us off the ground.
+        #
+        # what we're doing is looking for the null byte which 
+        while True:
+            byte = istream.read(1)
+            if not byte:
+                pass # Gtk.main_quit()
+            elif byte == b'\0':
+                win.set_dotcode(bytes(buf), preserve_viewport=not first)
+                buf = bytearray()
+                first = False
+            else:
+                buf += byte
+
+    if options.streaming_mode:
+        reader = Thread(target=read, daemon=True)
+        reader.start()
+
     Gtk.main()
 
+
 if __name__ == '__main__':
     main()

xdot/ui/window.py

@@ -706,15 +706,17 @@ def textentry_activate(self, widget, entry):
     def set_filter(self, filter):
         self.dotwidget.set_filter(filter)
 
-    def set_dotcode(self, dotcode, filename=None):
-        if self.dotwidget.set_dotcode(dotcode, filename):
+    def set_dotcode(self, dotcode, filename=None, preserve_viewport=False):
+        if self.dotwidget.set_dotcode(dotcode, filename, center=not preserve_viewport):
             self.update_title(filename)
-            self.dotwidget.zoom_to_fit()
+            if not preserve_viewport:
+                self.dotwidget.zoom_to_fit()
 
-    def set_xdotcode(self, xdotcode, filename=None):
-        if self.dotwidget.set_xdotcode(xdotcode):
+    def set_xdotcode(self, xdotcode, filename=None, preserve_viewport=False):
+        if self.dotwidget.set_xdotcode(xdotcode, center=not preserve_viewport):
             self.update_title(filename)
-            self.dotwidget.zoom_to_fit()
+            if not preserve_viewport:
+                self.dotwidget.zoom_to_fit()
 
     def update_title(self, filename=None):
         if filename is None: