Render graph

how_to/Change_28.md

@@ -0,0 +1,18 @@
+- k: Render graph
+
+`k` is supposed to be a visualization tool, but so far we've just printed a
+bunch of OIDs... Now comes the visualization part!
+
+There's a convenient file format called "dot" that can describe a graph. This is
+a textual format. We'll generate a graph of all commits and refs in dot format
+and then visualize it using the "dot" utility that comes with Graphviz.
+
+(If you're unfamiliar with dot or Graphviz please look it up online.)
+
+The graph will contain a node for each commit, that points to the parent commit.
+The graph will also contain a node for each ref, which points to the relevant
+commit.
+
+At this point, `ugit k` is fully functional and I encourage you to play with it.
+Create a crazy branching history and a bunch of tags and see for yourself that
+`ugit k` can draw all that visually.

ugit/cli.py

@@ -1,4 +1,5 @@
 import argparse
+import subprocess
 import sys
 import textwrap
 
@@ -110,14 +111,24 @@ def tag(args):
 
 
 def k(args):
+    dot = "digraph commits {\n"
+
     oids = set()
     for refname, ref in data.iter_refs():
-        print(refname, ref)
+        dot += f"'{refname}' [shape=note]\n"
+        dot += f"'{refname}' -> '{ref}'\n"
         oids.add(ref)
 
     for oid in base.iter_commits_and_parents(oids):
         commit = base.get_commit(oid)
-        print(oid)
+        dot += f"'{oid}' [shape=box style=filled label='{oid[:10]}']\n"
         if commit.parent:
-            print("Parent", commit.parent)
+            dot += f"'{oid}' -> '{commit.parent}'\n"
-    # TODO visualize refs
+
+    dot += "}"
+    print(dot)
+
+    with subprocess.Popen(
+        ["dot", "-Tgtk", "/dev/stdin"], stdin=subprocess.PIPE
+    ) as proc:
+        proc.communicate(dot.encode())