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, 58 insertions, 0 deletions

diff --git a/src/libvpsc/constraint.h b/src/libvpsc/constraint.h
new file mode 100644
index 000000000..3da7449cd
--- /dev/null
+++ b/src/libvpsc/constraint.h
@@ -0,0 +1,58 @@
+/**
+ * \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.
+ */
+
+#ifndef SEEN_REMOVEOVERLAP_CONSTRAINT_H
+#define SEEN_REMOVEOVERLAP_CONSTRAINT_H
+
+#include <iostream>
+#include "variable.h"
+
+class Constraint
+{
+	friend std::ostream& operator <<(std::ostream &os,const Constraint &c);
+public:
+	Variable *left;
+	Variable *right;
+	double gap;
+	double lm;
+	Constraint(Variable *left, Variable *right, double gap, bool equality=false);
+	~Constraint();
+	inline double slack() const { return right->position() - gap - left->position(); }
+	long timeStamp;
+	bool active;
+	bool visited;
+	bool equality;
+};
+#include <float.h>
+#include "block.h"
+static inline bool compareConstraints(Constraint *const &l, Constraint *const &r) {
+	double const sl = 
+		l->left->block->timeStamp > l->timeStamp
+		||l->left->block==l->right->block
+		?-DBL_MAX:l->slack();
+	double const sr = 
+		r->left->block->timeStamp > r->timeStamp
+		||r->left->block==r->right->block
+		?-DBL_MAX:r->slack();
+	if(sl==sr) {
+		// arbitrary choice based on id
+		if(l->left->id==r->left->id) {
+			if(l->right->id<r->right->id) return true;
+			return false;
+		}
+		if(l->left->id<r->left->id) return true;
+		return false;
+	}
+	return sl < sr;
+}
+
+#endif // SEEN_REMOVEOVERLAP_CONSTRAINT_H