/*
Copyright (C) 2006 Pedro Felzenszwalb

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
*/

#ifndef SEGMENT_GRAPH
#define SEGMENT_GRAPH

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include "image.h"
#include "misc.h"
#include "filter.h"
#include "pnmfile.h"
#include "disjoint-set.h"


// dissimilarity measure between pixels
static inline float diff(image<float> *r, image<float> *g, image<float> *b,
	int x1, int y1, int x2, int y2) {
	return sqrt(square(imRef(r, x1, y1) - imRef(r, x2, y2)) +
		square(imRef(g, x1, y1) - imRef(g, x2, y2)) +
		square(imRef(b, x1, y1) - imRef(b, x2, y2)));
}

// threshold function
#define THRESHOLD(size, c) (c/size)

typedef struct {
	float w;
	int a, b;
} edge;

bool operator<(const edge &a, const edge &b) {
	return a.w < b.w;
}

/*
* Segment a graph
*
* Returns a disjoint-set forest representing the segmentation.
*
* num_vertices: number of vertices in graph.
* num_edges: number of edges in graph
* edges: array of edges.
* c: constant for treshold function.
*/
universe *segment_graph(int num_vertices, int num_edges, edge *edges,
	float c) {
	// sort edges by weight
	std::sort(edges, edges + num_edges);

	// make a disjoint-set forest
	universe *u = new universe(num_vertices);

	// init thresholds
	float *threshold = new float[num_vertices];
	for (int i = 0; i < num_vertices; i++)
		threshold[i] = THRESHOLD(1, c);

	// for each edge, in non-decreasing weight order...
	for (int i = 0; i < num_edges; i++) {
		edge *pedge = &edges[i];

		// components conected by this edge
		int a = u->find(pedge->a);
		int b = u->find(pedge->b);
		if (a != b) {
			if ((pedge->w <= threshold[a]) &&
				(pedge->w <= threshold[b])) {
				u->join(a, b);
				a = u->find(a);
				threshold[a] = pedge->w + THRESHOLD(u->size(a), c);
			}
		}
	}

	// free up
	delete[] threshold;
	return u;
}

#endif
