Previously graph layout was done using the Kamada-Kawai layout algorithm

implemented in Boost.  I am replacing this with a custom implementation of
a constrained stress-majorization algorithm.

The stress-majorization algorithm is more robust and has better convergence
characteristics than Kamada-Kawai, and also simple constraints can be placed
on node position (for example, to enforce downward-pointing edges, non-overlap constraints, or cluster constraints).

Another big advantage is that we no longer need Boost.

I've tested the basic functionality, but I have yet to properly handle
disconnected graphs or to properly scale the resulting layout.

This commit also includes significant refactoring... the quadratic program solver - libvpsc (Variable Placement with Separation Constraints) has been moved to src/libvpsc and the actual graph layout algorithm is in libcola.

(bzr r1394)

1 files changed, 47 insertions, 0 deletions

diff --git a/src/libvpsc/constraint.cpp b/src/libvpsc/constraint.cpp
new file mode 100644
index 000000000..7c200878b
--- /dev/null
+++ b/src/libvpsc/constraint.cpp
@@ -0,0 +1,47 @@
+/**
+ * \brief A constraint determines a minimum or exact spacing required between
+ * two variables.
+ *
+ * Authors:
+ *   Tim Dwyer <tgdwyer@gmail.com>
+ *
+ * Copyright (C) 2005 Authors
+ *
+ * Released under GNU LGPL.  Read the file 'COPYING' for more information.
+ */
+
+#include "constraint.h"
+#include <cassert>
+Constraint::Constraint(Variable *left, Variable *right, double gap, bool equality)
+: left(left),
+  right(right),
+  gap(gap),
+  timeStamp(0),
+  active(false),
+  visited(false),
+  equality(equality)
+{
+	left->out.push_back(this);
+	right->in.push_back(this);
+}
+Constraint::~Constraint() {
+	Constraints::iterator i;
+	for(i=left->out.begin(); i!=left->out.end(); i++) {
+		if(*i==this) break;
+	}
+	left->out.erase(i);
+	for(i=right->in.begin(); i!=right->in.end(); i++) {
+		if(*i==this) break;
+	}
+	right->in.erase(i);
+}
+std::ostream& operator <<(std::ostream &os, const Constraint &c)
+{
+	if(&c==NULL) {
+		os<<"NULL";
+	} else {
+		const char *type=c.equality?"=":"<=";
+		os<<*c.left<<"+"<<c.gap<<type<<*c.right<<"("<<c.slack()<<")"<<(c.active?"-active":"");
+	}
+	return os;
+}